Textbook of Radiology for CT and MRI Technicians with MCQs (Jan 1, 2018)_(9352701763)_(Jaypee brothers medical publishers) 9789352701766, 9741283608

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Sachin Khanduri

Textbook of

Radiology

for CT and MRI Technicians with MCQs

Textbook of

Radiology

for CT and MRI Technicians with MCQs

Sachin Khanduri MD Professor and Head Department of Radiology Era’s Lucknow Medical College Lucknow, Uttar Pradesh, India

The Health Sciences Publisher New Delhi | London | Panama

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Website: www.jaypeebrothers.com Website: www.jaypeedigital.com © 2018, Jaypee Brothers Medical Publishers The views and opinions expressed in this book are solely those of the original contributor(s)/author(s) and do not necessarily represent those of editor(s) of the book. All rights reserved. No part of this publication may be reproduced, stored or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission in writing of the publishers. All brand names and product names used in this book are trade names, service marks, trademarks or registered trademarks of their respective owners. The publisher is not associated with any product or vendor mentioned in this book. Medical knowledge and practice change constantly. This book is designed to provide accurate, authoritative information about the subject matter in question. However, readers are advised to check the most current information available on procedures included and check information from the manufacturer of each product to be administered, to verify the recommended dose, formula, method and duration of administration, adverse effects and contraindications. It is the responsibility of the practitioner to take all appropriate safety precautions. Neither the publisher nor the author(s)/editor(s) assume any liability for any injury and/ or damage to persons or property arising from or related to use of material in this book. This book is sold on the understanding that the publisher is not engaged in providing professional medical services. If such advice or services are required, the services of a competent medical professional should be sought. Every effort has been made where necessary to contact holders of copyright to obtain permission to reproduce copyright material. If any have been inadvertently overlooked, the publisher will be pleased to make the necessary arrangements at the first opportunity. The CD/DVD-ROM (if any) provided in the sealed envelope with this book is complimentary and free of cost. Not meant of sale. Inquiries for bulk sales may be solicited at: [email protected] Textbook of Radiology for CT and MRI Technicians with MCQs First Edition: 2018 ISBN: 978-93-5270-176-6

Dedicated to My loving and supportive parents

Dr OP Khanduri

Dr Sushila Khanduri

Preface “It is the supreme art of the teacher to awaken joy in creative expression and knowledge.” It is indeed with a great sense of pleasure that I write this preface to “Textbook of Radiology for CT and MRI Technicians with MCQs.” • The current academic scenario in our country has witnessed an abundance of technician courses in Radiology. An offshoot of this has been the burgeoning demand for reliable sources of knowledge for these courses. The mushrooming number of textbooks is a welcome sign of enterprise and effort on the part of our teachers. However, all are met of acceptable quality. One needs to separate the wheat from the chaff and restrict one’s interest to the textbook with quality content. One such material is this textbook. • This book is structured into three parts namely Introduction to Radiology, Computed Tomography and Magnetic Resonance Imaging which widely cover the subject. A group of focused residents and researchers have helped compile these parts. • We have incorporated chapters on Recent imaging sciences in CT and MRI, PET-MRI etc. along with fundamental topics in Radiology, thus providing a blend of basic and advance knowledge. MCQs are added at the end of each chapter which will be helpful for the examinations. • All the postgraduate students in our department have done outstanding job in helping me write this text into a valued resource for each student. I wish them all the best in their endeavor to spread knowledge. • I strongly recommend this book for all the Radiology technicians. They will be immensely benefitted with this new armamentarium in their field. My best wishes are with this book.

Sachin Khanduri

Acknowledgments • I am indebted to the management of Era’s Lucknow Medical College, who have been supportive of my career goals and have worked actively to provide me with the protected academic environment to pursue these goals. • I am grateful to all the postgraduate residents with whom I had the pleasure to work during this and other related projects. Each of the resident and my fellow faculty members have provided me with extensive professional guidance and taught me a great deal about both scientific-research and life in general. I am thankful to Dr Tushar Sabharwal and Dr Amit Mishra for their hardwork and dedication. • I am also thankful to Professor Emeritus Dr Samarjit Bhadury for being a source of inspiration. • I would especially like thank my brother, Dr Arun Khanduri who has taught me more than I could even give him credit for here. He has given me immense self-belief to reach this stage. • Most importantly, I wish to thank my loving and supportive wife, Dr Shobha Khanduri who has always stood by me and my two wonderful children Satvik and Ritvik who provide unending inspiration and reason to push forward. Sachin Khanduri

Contents

Color Plates

Part 1: Introduction to Radiology 1.

Basics of Radiology.................................................................................................................................................3 • Radiology Modalities  3 • Ionizing Radiation  3 • Nonionizing Radiation  4  • X-rays 4 • Ultrasound 5 • Computed Tomography Scan  7 • Magnetic Resonance Imaging  8 • Multiple Choice Questions  9



2.

Role of Contrast....................................................................................................................................................11 • Types of Contrast Media  11 • Properties of Ideal Contrast Media  11 • Side Effects and Reactions  11 • Prevention of Reactions  11 • Treatment of Contrast-mediated Adverse Reaction  11 • Contrast Agents in Computed Tomography (Sometimes Also Called Dyes)  12 • Magnetic Resonance Imaging Contrast Agents  13 • Multiple Choice Questions  15



3.

Radiation Hazards and Protection......................................................................................................................17 • Regulatory Body  17 • Sources of Radiation  17 • Radiation Hazards  17 • Biological Effects of Radiation  19 • Principles of Radiation Protection  20  • Radiation Protection  22 • Multiple Choice Questions  25

Part 2: Computed Tomography 4.

Computed Tomography Physics..........................................................................................................................29 • Principles 29 • Computed Tomography Methodology  29 • Advantages of Computed Tomography over Conventional Radiography  33 • Disadvantage of Computed Tomography over Conventional Radiography  34 • Advantages of Computed Tomography over Magnetic Resonance Imaging  34 • Disadvantages of Computed Tomography over Magnetic Resonance Imaging  34 • Multiple Choice Questions  34

xii  Textbook of Radiology for CT and MRI Technicians with MCQs 5.

Indications and Contraindications......................................................................................................................37 • Indications for Use of Computed Tomography  37 • Contraindications 39 • Contraindications for the Use of Contrast Media  39 • Contrast Medium  39 • Pressure Injectors  40 • Multiple Choice Questions  44

6.

Patient Preparation, Positioning and Contrast Administration.......................................................................45 • Patient Positioning for Computed Tomography Scan  45 • Contrast 47 • Computed Tomography: Abdomen and Pelvis  48 • Malignancy and Acute Pancreatitis  49 • Retrospective Reconstruction  50 • Routine Abdomen or Pelvis  50 • Routine Chest, Abdomen and Pelvis  51 • Retroperitoneal Hemorrhage (AKA Noncontrast Abdomen/Pelvis)  51 • Trauma 51 • Computed Tomography Cystography  52 • Triple Phase Liver: Hepatocellular Carcinoma  52 • Dual Phase Liver (Arterial, Portal Venous, Delay)  52 • Adrenal Mass  53 • Renal Mass  53 • Renal Infection (Not a Protocol)  53 • Renal Stone  53 • Renal Artery Stenosis  54 • Renal Ureteropelvic Junction/Donor  54 • Computed Tomography Urography  54 • Pancreatic Mass  54 • Computed Tomography Enterography  55 • Computed Tomography Colonography  55 • Aortic Dissection  56 • Aortic Aneurysm—Pre-endovascular Stent  56 • Aortic Aneurysm—Post-endovascular Stent  56 • Computed Tomography Pelvis without Abdomen  56 • Multiple Choice Questions  56

7.

Computed Tomography Anatomy.......................................................................................................................59 • Multiple Choice Questions  59

8.

Basic Computed Tomography Pathologies.........................................................................................................65 Head  65 • Brain Hematomas  65 • Ischemic Stroke  65 • Neurocysticercosis 66 • Brain Tumors  67 • Cerebral Arteriovenous Malformation  67



 Contents xiii • Brain Abscess  67 • Metastasis to Brain  68 Thorax  68 • Tuberculosis 68 • Occupational Lung Diseases  69 • Bronchogenic Carcinoma  69 • Mediastinal Masses  70 Hepatobiliary System  71 • Gallbladder Carcinoma  71 • Cholelithiasis 72 • Cholangiocarcinoma 72 • Hepatic Hemangioma  73 Pancreas  74 • Acute Pancreatitis  74 • Pancreatic Pseudocyst  74 • Computed Tomography Findings  75 Genitourinary Tract: Renal  76 • Urolithiasis (Urinary Tract Calculus)  76 • Renal Cell Carcinoma  76 • Autosomal Dominant Polycystic Kidney Disease  76 Urinary Bladder  77 • Transitional Cell Carcinoma of the Bladder  77 • Multiple Choice Questions  78

9.

Recent Advances in Computed Tomography......................................................................................................80 • Advances in Hardware  80 • Cone-beam Computed Tomography Scanner  80 • Multidetector Computed Tomography  81 • Dual Energy Computed Tomography  82 • Positron Emission Tomography Scan  82 • Electron Beam Tomography  85 • Computed Tomography Coronary Angiography  85 • Computed Tomography Angiography  86 • Multiple Choice Questions  87

10.

Computed Tomography-guided Interventions..................................................................................................89 • Materials and Techniques  90 • Desirable Equipment  90 • Computed Tomography-guided Procedure: Steps  90 • Main Risks and Complications of Computed Tomography-guided Interventions  92 • Pitfalls 93 • Key Points  93 • Multiple Choice Questions  94

11.

Computed Tomography Angiography................................................................................................................95 • Indications 95 • Contraindications 95



xiv  Textbook of Radiology for CT and MRI Technicians with MCQs • Risk Factors  96 • Benefits  96 • Carotid Angiography  96 • Subclavian Angiography  96 • Pulmonary Angiography  97 • Thoracoabdominal Aorta  97 • Renal Angiography  97 • Mesenteric Angiography  97 • Iliac Angiography  97 • Computed Tomography Portography  98 • CT Arteriography/CT Arterioportography  98 • Multiple Choice Questions  98 12.

Computed Tomography Artifacts......................................................................................................................100 • Classification 100 • Motion Artifact  100 • Ring Artifact  100 • Noise 100 • Beam Hardening and Scatter  101 • Partial Volume Artifact  102 • Photon Starvation  102 • Metal Artifact  103 • Out of Field “Artifact”  103 • Tube Arcing  104 • Cone-beam (Multidetector Row) and Windmill (Helical) Artifacts  104 • Future Perspective  104 • Multiple Choice Questions  105

Part 3: Magnetic Resonance Imaging 13.

Magnetic Resonance Imaging Physics..............................................................................................................109 • Components of MRI System  109 • Magnet 109 • Shim Coils  110 • Gradient Coils  110 • Receiver Coils/Radiofrequency Transmitters  111 • Computer 112 • Multiple Choice Questions  114 MRI Sequences  115 • Characteristics of an MRI Sequence  115 • Sequence Classification  115 • Multiple Choice Questions  119

14.

Indications, Contraindications, Patient Preparation and Positioning...........................................................121 • Indications 121 • Contraindications 121 • Positioning and Patient Preparation  122

 Contents xv • Magnetic Resonance Cholangiopancreatography (MRCP)  127 • Enterography  128 • Enteroclysis 128 • Defecography 129 • Multiple Choice Questions  130 15.

Magnetic Resonance Imaging Anatomy...........................................................................................................132 • Multiple Choice Questions  132

16.

Basic Magnetic Resonance Imaging Pathologies.............................................................................................141 Bone Tumors  141 • Classification 141 • Bone Tumors: Introduction  141 • Basic View  142 • Benign Bone Tumors  142 • Malignant Bone Tumors  146 • Multiple Choice Questions  147 Central Nervous System  148 • Dandy-Walker Malformations  148 • Arnold-Chiari Malformation  148 • Intracranial Infections  148 • White Matter Disease  150 • Dysmyelination Diseases  151 • Intracranial Hemorrhage  151 • Hypoxic-Ischemic Encephalopathies  153 • Intracranial Neoplasm  154 • Multiple Choice Questions  156 Hepatobiliary System  157 • Liver 157 • Pancreas 162 • Spleen 164 • Common Bile Duct  165 • Gallbladder 166 • Portal Vein  167 • Multiple Choice Questions  169 Magnetic Resonance Imaging Thorax  170 • Mediastinum 170 • Malignant Pleural Diseases  171 • Aorta 172 • Heart and Pericardium  172 • Multiple Choice Questions  174 Shoulder Joint  175 • Rotator Cuff Tears  175 • Multiple Choice Questions  178 Knee Joint  179 • Indications of Knee Joint Magnetic Resonance Imaging  179 • Meniscal Tears  179

xvi  Textbook of Radiology for CT and MRI Technicians with MCQs

• Cruciate Ligaments Injury  179 • Multiple Choice Questions  182 Wrist Joint  183 • Carpal Tunnel Syndrome  183 • Multiple Choice Questions  184 Degenerative Diseases of Spine  185 • Spondylosis 185 • Disk Bulge  186 • Disk Herniation  186 • Trauma 186 • Tumors 187 • Metastatic Disease  187 • Multiple Choice Questions  189 Infection of Bones  190 • Tuberculosis 190 • Pyogenic Infections  192 • Multiple Choice Questions  194 Infections of Spine  195 • Tuberculosis 195 • Pyogenic Infections  197 • Multiple Choice Questions  199

17.

Recent Advances in the Field of Magnetic Resonance Imaging......................................................................200 • Functional Magnetic Resonance Imaging  200 • Magnetic Resonance Spectroscopy  202 • Magnetic Resonance Elastography  202 • Positron Emission Tomography–Magnetic Resonance Imaging  202 • Real-time Magnetic Resonance Imaging  205 • Cardiovascular Magnetic Resonance Imaging  208 • Multiple Choice Questions  208

18.

Magnetic Resonance Imaging Artifacts............................................................................................................210 • Artifacts 210 • Zipper Artifact  210 • Herringbone Artifact  211 • Zebra Stripes/Artifacts  211 • Moire Fringes  211 • Radiofrequency Overflow Artifact  212 • Slice-overlap Artifact  213 • Cross-excitation Artifact  213 • Phase-encoded Motion Artifact  214 • Black Boundary Artifact  214 • Magnetic Susceptibility Artifacts (Susceptibility Artifact)  215 • Chemical Shift Artifact or Misregistration  216 • Dielectric Effect Artifact  216 • Multiple Choice Questions  218

 Index........................................................................................................................................................................................................................221

Color Plate 1

Fig. 1: A 22-year-old male patient with acoustic schwannoma. Contrast MRI brain (axial, coronal and sagittal) and diffusion images showing welldefined rounded homogenously enhancing lesion in bilateral cerebello-pontine angles.

Color Plate 2

Fig. 2: Normal CT aortogram. Contrast enhanced CT aortogram images obtained with volume rendered technique (VRT) demonstrates thoracic and abdominal aorta with abdominal branches and common iliac arteries.

A

B Fig. 3:  A 33-year-old male patient of cholecystoduodenal fistula. Contrast enhanced axial CT abdomen images demonstrate contracted gallbladder lumen with wall thickening and fistulous communication with duodenum and evidence of calculus within duodenal lumen.

Color Plate 3

Fig. 4: A 20-year-old male patient with chondrosarcoma. CT volume rendered technique (VRT) image demonstrates rib destruction with mass lesion.

Fig. 5: Normal CT cerebral angiogram. Contrast enhanced CT images demonstrated circle of Willis and carotid arteries.

Fig. 6: A 65-year-old female patient with gout. CT volume rendered technique (VRT) image demonstrates uric acid crystals (green color) in joints of foot.

Fig. 7: Normal lower limb CT peripheral angiography. CT maximum intensity projection (MIP) and volume rendered technique (VRT) images demonstrate lower limb arteries.

Color Plate 4

Fig. 8: Normal coronary CT angiogram. CT volume rendered technique (VRT) images demonstrate heart with its coronary arterial supply.

Fig. 9: Normal CT urography. Contrast enhanced CT urography demonstrated normal pelvicalyceal system, ureters and bladder on coronal sections and volume rendered technique (VRT) image.

Color Plate 5

Fig. 10: DECT metal artifact reduction. Dual energy CT images demonstrates metal artefact reduction on progressive keV images.

Color Plate 6

Fig. 11:  A 20-year-old female patient with primary osseous hemangioma. Sagittal CT image (bone window) demonstrates thickened trabecular pattern in occipital bone with bony expansion.

Fig. 12: A 50-year-old female with pelvic fracture. CT volume rendered technique (VRT) image demonstrates comminuted fracture of left iliac bone.

Fig. 13: A 30-year-old male patient of potts spine. MRI T2 coronal image demonstrates vertebral body destruction and collection in left psoas muscle.

Color Plate 7

Fig. 14: A 60-year-old female with pulmonary embolism. CT MIP and volume rendered technique (VRT) images demonstrate non-visualization of right upper and middle lobar pulmonary arteries due to embolism.

Fig. 15: A 21-year-old patient with Hirayama disease. Flexion T1 contrast MRI sagittal image demonstrates anterior displacement of the dorsal dura compressing the thecal sac.

Color Plate 8

Fig. 16: DECT renal stone characterization. Dual energy CT images demonstrate uric acid stone (red color) in right ureter.

Fig. 17: CECT dual energy lung perfusion images. Contrast enhanced dual energy sagittal, coronal, axial and volume rendered technique (VRT) images demonstrate reduced perfusion of left lung.

P A R T

1

Introduction to Radiology

C H A P T E R S 1. Basics of Radiology 2. Role of Contrast 3. Radiation Hazards and Protection

1 C H A P T E R

Basics of Radiology

DEFINITION

IONIZING RADIATION

Radiology is a medical specialty that uses imaging to diagnose and treat diseases seen within the body.

Ionizing radiation is radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them.

RADIOLOGY MODALITIES (FIG. 1)

Types

• Conventional radiography (X-rays) including: –– Fluoroscopy –– Mammography • Computed tomography (CT) • Ultrasonography (USG) • Magnetic resonance imaging (MRI) • Nuclear medicine (NM) –– Positron emission tomography (PET)-CT combines CT and NM –– PET-MRI combines MRI and NM.

• Alpha radiation • Beta radiation • Gamma radiation • X-rays • Neutrons

Modalities • X-rays • CT-scan • PET scan

Endoscopic retrograde cholangiopan­ creatography (ERCP) Bone scans Thyroid scan

Fig. 1: Increasing energy and wavelength of visible light.

4  Introduction to Radiology

NONIONIZING RADIATION Nonionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum (photon energy) to ionize atoms or molecules, i.e. to completely remove an electron from an atom or molecule.

X-ray wavelengths are shorter than those of ultraviolet (UV) rays and typically longer than those of gamma rays.

Medical Uses

X-radiation is referred to with terms meaning Röntgen radiation, after Wilhelm Röntgen, who is usually credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation. X-radiation (composed of X-rays) is a form of electro­ magnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 3 × 1,016 Hz to 3 × 1,019 Hz and energies in the range 100 eV–100 keV.

• A radiograph is an X-ray image that is acquired by placing the body part under consideration in front of an X-ray detector and illuminating it with a short X-ray pulse. Bones are the richest in calcium, which by virtue of its relatively high atomic number absorbs X-rays with ease. This markedly decreases the amount of X-rays reaching the detector that come in the shadow of the bones, making them prominent on the radiograph. The lungs along with the trapped gas are also prominent due to their low rate of absorption as compared to tissue. Differentiation between different tissues is not so easily noted. • Radiographs are also helpful in unmasking the patho­ logy of the skeletal system (Fig. 3) as well as the soft tissue disease processes. Some eminent illustrations are the routine chest X-ray, which are very often used to identify lung diseases like pneumonia, lung cancer or pulmonary edema, and the abdominal X-ray, which can recognize bowel (or intestinal) obstruction, free air (from visceral perforations) and free fluid (in ascites). X-rays are also used to identify pathologies, for instance, gallstones (which are seldom radiopaque) or the kidney stones that are most commonly (but not invariably) visible. Conventional plain X-rays are less effective in the imaging of soft tissues like the brain or muscle. • Dental radiography is frequently useful in the diagnosis of familiar oral problems like cavities.

A

B

Types • Infrared • Microwaves • Radiowaves • Ultraviolet

Modalities • Magnetic resonance imaging • Magnetic resonance cholangiopancreatography (MRCP)

X-RAYS • X-rays were invented on November 8, 1895 by Sir Wilhelm Conrad Röntgen • 1901: Received Nobel Prize for it.

Conventional X-rays (Figs. 2A and B)

Figs. 2A and B: X-ray tube and its various components.

  Basics of Radiology  5 chest X-rays are done at a distance of 180 cm (or 6 ft) to reduce the magnification of heart and apical lordotic view to visualize lung apices (Fig. 4). • Radiosensitive material: Radiosensitive films are coated with radiosensitive material that converts invisible X-rays to detectable image—silver bromide. –– Single-coated films are preferred and are of better resolution. –– Double-coated films provide more information and are used in dental radiography.

Digital Radiography

Fig. 3: Postoperative image showing plating of radius and ulna in forearm.

• X-ray filters: In medical diagnostic applications, the low-energy (soft) X-rays are undesirable, as they are entirely absorbed by the body, thus increasing the radiation dose without adding to the image. Hence, a thin metal sheet, frequently of aluminium, which is called an X-ray filter, is most commonly placed over the window of the X-ray tube, absorbing the low energy part in the spectrum. This is known as hardening the beam as it shifts the center of the spectrum toward the higher energy (or harder) X-rays. • Digital subtraction angiography: To develop an image of the cardiovascular system along with the arteries and veins (angiography), an antecedent image is obtained of the anatomical region of interest. A second image is then captured of the same region post injection of an iodinated contrast agent into the blood vessels within this area. These two images are then digitally subtracted, thus leaving an image of only the iodinated contrast outlining the blood vessels. The image, thus obtained, is compared to the normal anatomical images, by the radiologist or surgeon, to determine if there is any damage or blockage of the vessel. • Most radiographs are done at a distance of 100 cm (or 3 ft) but there are several modifications to technique to better visualize specific region in chest. For example,

• Digital radiography is a form of X-ray imaging, where digital X-ray sensors are used instead of traditional photographic film (Fig. 5). • Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography. • Types: –– Computed radiography –– Direct radiography

ULTRASOUND • Principle: Piezoelectricity –– Crystal used—PZT (Lead zirconate titanate) • Frequency of probe used ranges from 2 MHz to 20 MHz –– More the frequency of probe—Better resolution –– Lesser the frequency of probe—More depth • Thin and superficial body parts—High frequency probe (7–15 MHz) –– Thick and deep body parts—Low frequency probe (2–7 MHz) –– Obstetric ultrasound—3.5–7.0 MHz • Image interpretation in ultrasound study –– Black—Anechoic/Hypoechoic –– White—Echogenic/Hyperechoic –– Reference/Similar—Isoechoic Examples: • Hyperechoic/Echogenic: Calculus, fat, air and vessels • Hypoechoic: Muscles, lymph nodes and cartilage Other terms are commonly used in ultrasound study: • Acoustic enhancement—marker of a cystic lesion • Acoustic shadow—marker for calculus. Most important role of ultrasound is in differentiating between solid and cystic lesions.

6  Introduction to Radiology

Fig. 4: Chest X-ray with labeling of structures to be assessed.

Fig. 5: Model layout of X-ray installation.

  Basics of Radiology  7

Why We Use Jelly for USG?

COMPUTED TOMOGRAPHY SCAN

• When using ultrasound, it is commonplace to apply a gel, which consists mostly of water, as a contact medium between the tissue (i.e. the skin) and the ultrasound head. • The purpose of the gel is to convey the sound energy from the ultrasound transducer head to the tissue without crossing through the air at any point. • The reason, this is important, is that both reflection and refraction are markedly less when crossing from a gel into body tissues than they are when crossing from air into body tissues.

A CT scan, also called X-ray computed tomography (X-ray CT) or computerized axial tomography scan (CAT scan), makes use of computer-processed combinations of many X-ray images taken from different angles to produce cross-sectional (tomographic) images (virtual “slices”) of specific areas of a scanned object, allowing the user to see inside the object without cutting. Computed tomography scanners were first made known in 1971 with a single detector for studying the brain under the command of Sir Godfrey Newbold Hounsfield, who was an electrical engineer at EMI (Electric and Musical Industries Ltd). Thenceforth, it has borne enumerable changes with increase in number of detectors and decrease in the scan time. For his work in the field of CT-imaging, he received Nobel Prize in 1973. • First generation: –– Number of detectors: One –– Duration of scan (average): 25–30 minutes. • Second generation: –– Number of detectors: Multiple (up to 30) –– Duration of scan (average): Less than 90 seconds. • Third generation: –– Number of detectors: Multiple, originally 288; newer ones use over 700 arranged in an arc –– Duration of scan (average): Approximately 5 seconds. • Fourth generation: –– Number of detectors: Multiple (more than 2,000) arranged in an outer ring which is fixed –– Duration of scan (average): Few seconds. • Other technologies: Other CT technologies have been adapted to third and fourth generation scanners, including: –– Helical (spiral) image acquisition—used in all modern CT machines –– Dual energy CT scanning (Fig. 6).

Types of Ultrasonography • A-mode: A-mode (amplitude mode) is the most uncomplicated type of ultrasound. In this, the cathoderay tube display one axis represents the time required for the return of the echo and the other corresponds to the strength of the echo, e.g. A-mode scan for axial length of eyeball in ophthalmology. • B-mode or 2D mode: In B-mode (brightness mode) ultrasound, the position of a spot on the CRT display corresponds to the time elapsed (and thus to the position of the echogenic surface) and the brightness of the spot to the strength of the echo; movement of the transducer produces a sweep of the ultrasound beam and a tomographic scan of a cross-section of the body. More commonly known as 2D mode now, e.g. most of the ultrasounds on various bodies. • C-mode: A C-mode, mainly used in industry testing, in which image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in around 10 seconds. • M-mode: Time-motion displays a modality in which the echo signal is recorded on a continuously moving strip of paper, when the transducer is held in a fixed position over the aortic or mitral valves; each dot corresponding to a moving structure has a sinewy path, while stationary structures are represented as straight lines. • Doppler mode: This mode makes use of the Doppler effect in measuring and visualizing blood flow.

Benefits1 • CT scanning is harmless, non-invasive and accurate. • CT can image all parts of the body at the same time, whether it be bones or soft tissues or blood vessels along with providing detailed imaging of all. • CT examinations are quick and simple which help in emergency situations to find out internal injuries and bleeding for quick action. • CT is a very worthy-for-money investigation for all clinical purposes.

8  Introduction to Radiology

Fig. 6: Model layout for CT scan.

• CT is less sensitive to patient movement than MRI. • CT can be performed if you have an implanted medical device of any kind, unlike MRI. • CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis, and bones. • A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy. • No radiation remains in a patient’s body after a CT exami­ nation, but in case of nuclear medical imaging a small amount of radiation can stay in the body for a short time.

Risks • There are still debates over the risk of developing cancer with the amount of the radiation that CT scan delivers. • The effective radiation dose for this procedure varies. • In general, due to its radiation doses, CT is not recommended for pregnant females as it may carry risks for the fetus. • Manufacturers of intravenous contrast indicate mothers should not breastfeed their babies for 24–48 hours after contrast medium is given.

• The risk of serious allergic reaction to contrast mate­ rials that contain iodine is extremely rare, and radio­logy departments are well-equipped to deal with them.

MAGNETIC RESONANCE IMAGING • Principle: Gyromagnetic property of proton. • Just after the end of World War II, two physicists, Felix Bloch and Edward Mills Purcell, simultaneously discovered nuclear magnetic resonance (NMR). • The use of MRI, initially known as NMR, to produce 2D images was accomplished by Paul Lauterbur and Sir Peter Mansfield. They received Nobel Prize for this discovery in 2003.

Advantages • Unlike CT scanning, MRI has the capacity to image without the use of ionizing radiation (X-ray) • Images can be acquired in multiple planes (Axial, Sagittal, Coronal, or Oblique) without discomfort to the patient. CT images have only recently been able to reconstruct images in multiple planes with the same spatial resolution.

  Basics of Radiology  9 • MRI images exhibit far superior soft-tissue contrast than CT scans and plain films, thus making it the ideal examination for the brain, spine, joints and other softtissue body parts. • Unlike CT or conventional angiography, angiographic images can also be obtained without the use of contrast material. • Detailed and specific tissue characterization is made possible with advanced techniques, such as diffusion, spectroscopy and perfusion. • Functional MRI allows visualization of both active parts of the brain during certain activities and understanding of the underlying functioning of different parts of the brain.

Disadvantages • MRI scans are costlier than CT scans • The time taken for a single scan is longer and hence patient comfort is an issue. • The images taken by the MRI have artifacts that are difficult to eradicate and hinder in proper visua­ lization.

• It cannot be used in patients with metal fragment or device in the body like: –– Cardiac pacemakers –– Free lying metallic foreign body –– Bullet in body –– Hemostatic aneurysmal clips –– Cochlear implants –– Metallic cardiac valves • Claustrophobia • 1st trimester pregnancy –– Metal implants—not an absolute contraindication— as are made of titanium and are not free lying in the body. But heating occurs. –– Tattoos with heavy metals—heating occurs. –– Copper-T—not a contraindication.

REFERENCE 1. (ACR) R. Body CT (CAT Scan) [Internet]. Radiologyinfo. org. 2017 [cited 21 June 2017]. Available from: https://www. radiologyinfo.org/en/info.cfm?pg=bodyct

MULTIPLE CHOICE QUESTIONS











1. Modalities of radiology are all except: a. Positron emission tomography-computed tomography (PET-CT) b. Ultrasonography c. Laparoscopy d. Magnetic resonance imaging 2. X-ray invented by: a. Becquerel c. Wilhelm Röntgen

b. Christian Johann d. Adriaen Block

3. Piezoelectric crystal used in USG: a. Quartz b. Lead zirconate titanate c. Vibranium d. Kryptonite 4. Magnetic resonance imaging is based on gyromagnetic property of: a. Fe b. Proton c. Carbon d. Calcium 5. Advantage of CT over X-ray imaging: a. Low radiation

b. Faster c. Cheaper d. 3D image reconstruction

6. Modes of ultrasound are all except: a. A mode b. C mode c. D mode d. M mode



7. Duration of scan for first generation CT machine: a. 50 seconds b. 25–30 seconds c. 80–90 seconds d. 25–30 minutes



8. Year of introduction of CT scanners: a. 1971 b. 1969 c. 1989 d. 1972



9. Number of detectors in third generation CT machi­ nes: a. 701 b. 800 c. 700 d. 699

10. Duration for nonbreastfeeding of baby after intravenous contrast CT scan of mother: a. 24–36 hours b. 12–24 hours c. 24–48 hours d. 48–54 hours

10  Introduction to Radiology 11. Use of NMR in MRI accomplished by: a. Paul Lauterbur b. Edward Mills Purcell c. Wilhelm Röntgen d. Felix Bloch

16. Frequency of probe used in obstetric ultrasound: a. 3.5–7 MHz b. 2–7 MHz c. 7–15 MHz d. 8–12 MHz

12. Advantage of MRI over CT: a. Cheaper b. Non-use of ionizing radiation c. Faster d. Assessment of bony cortex

17. CT was introduced by: a. Godfrey Hounsfield b. Edward Mills Purcell c. Wilhelm Röntgen d. Felix Bloch

13. Which is not a type of nonionizing radiation? a. Soundwaves b. Microwaves c. Infrared d. Radiowaves 14. Not a modality of nonionizing radiation: a. Ultrasonography (USG) b. Magnetic resonance cholangiopancreatography (MRCP) c. X-rays d. Magnetic resonance imaging (MRI) 15. Coating of radiosensitive films: a. Copper b. Silver bromide c. Silver nitrate d. Aluminum

18. Dual energy CT scanning belongs to which generation of CT scan machines: a. First generation b. Third generation c. Other technologies d. Second generation 19. Godfrey Hounsfield received a Nobel Prize for introduction of CT machine: a. 1974 b. 1980 c. 1971 d. 1973 20. Distance for performing a chest X-ray: a. 6 ft b. 4 ft c. 7 ft d. 3 ft

ANSWERS 1. c 9. c 17. a

2. c 10. c 18. c

3. b 11. a 19. d

4. b 12. b 20. a

5. d 13. a

6. c 14. d

7. d 15. b

8. a 16. a

2 C H A P T E R

Role of Contrast

INTRODUCTION

Dose Dependent

Contrast medium is a substance, which is used to image organs and fluids within the body cavity after introduction of contrast into the body cavity or vessels to help visualize the structures or pathology.

Dose-dependent systemic adverse effect can occur with the contrast media like nausea, vomiting, metallic taste in mouth and flushing.

TYPES OF CONTRAST MEDIA

Reactions that occur after 30 minutes of administration of contrast medium are called delayed reaction. It usually occurs with ionic contrast agents. Its symp­ toms resemble flu like syndrome with fever, chills, nausea, vomiting, and abdominal pain.

Several types of contrast media are used. They are mainly classified into: • Positive contrast media: Positive contrast media have high atomic weight, e.g. barium sulfate and iodine. • Negative contrast media: Negative contrast media have low atomic weight, e.g. air, oxygen, and carbon dioxide.

PROPERTIES OF IDEAL CONTRAST MEDIA • Osmolarity: An ideal contrast should have low osmo­ larity. An agent with high osmolarity has more side effects. • Viscosity: It should be as per the requirement of organ to be investigated. High viscosity contrast agents take more time to get excreted from kidneys thereby causing more damage. While when viewing the gastrointestinal tract (GIT), high viscosity contrast such as barium is used for a better contrast. • Toxicity: It should be nontoxic and safe. • It should be adequately miscible for examination. • Better coating properties of the gastrointestinal mucosa.

SIDE EFFECTS AND REACTIONS Modern contrast media are safe to use but reactions can occur which can range from minor urticaria to death.

Dose Independent Anaphylactic Shock Serious potentially life-threatening reaction may occur with administration of contrast, i.e. acute bronchospasm and hypotension.

Delayed Reactions

Extravasation of Contrast Media These are caused by direct toxic effect of contrast medium causing tissue damage.

PREVENTION OF REACTIONS • Avoid using contrast media over 50 years of age or patient with history of obesity, alcoholism, coronary artery disease, and hypertension. • Patient on b-blockers • Sedatives like diazepam can be used to sedate the patient. • Use of steroids before 24 hours of administration of contrast media.

TREATMENT OF CONTRAST-MEDIATED ADVERSE REACTION Anaphylactic Reaction (Flowchart 1) • Mild cases like urticaria may be treated with chlor­ pheniramine maleate. • Severe cases like edema of glottis and pulmonary edema should be treated with furosemide (lasix). • 100% oxygen face mask and bag ventilation. • Adrenalin 0.5 mL (1:1,000) subcutaneously (SC). • Methyl prednisolone or hydrocortisone succinate in dose of 40 mg and 100 mg respectively.

12  Introduction to Radiology Flowchart 1: Anaphylactic reactions: Treatment for adults by first medical responders.

Notes: *An inhaled b2 agonist such as salbutamol may be used as an adjunctive measure if bronchospasm is severe and does not respond rapidly to other treatment. † If profound shock judged immediately life-threatening give CPR/ALS, if necessary. Consider slow intravenous (IV) adrenaline (epinephrine) 1:10,000 solution. This is hazardous and is recommended only for an experienced practitioner who can also obtain IV access without delay. Note the different strength of adrenaline (epinephrine) that may be required for IV use. ‡ If adults are treated with an EpiPen®, the 300 μg will usually be sufficient. A second dose may be required. Half doses of adrenaline (epinephrine) may be safer for patients on amitriptyline, imipramine, or b-blocker. § A crystalloid may be safer than a colloid.

• If required tracheostomy puncture should be done. • Generalized convulsions should be treated with injection diazepam 10 mg slow intravenously (IV). • In cases of hypotension with peripheral circulatory failure. –– Lay patient flat –– Administer adrenalin 0.5 mg (1:1,000) intramuscu­ larly (IM) repeat every 5 minutes, if needed. –– Hydrocortisone succinate 100 mg IV. • Cardiac arrest –– Clear the airways and extended head and push lower jaw forward

–– Give mouth-to-mouth respiration –– Put the patient on cardiac monitoring and defibrillator.

CONTRAST AGENTS IN COMPUTED TOMO­­ GRAPHY (SOMETIMES ALSO CALLED DYES) Computed tomography contrast agents are used to enhance specific lesions in an organ, tissues or in blood vessels. Contrast media are of three types based on route of administration: 1. Oral

  Role of Contrast  13 2. Intravenous 3. Enema

Oral Contrast Media Oral contrast media are of two types: 1. Barium sulfate is the most common contrast taken orally and can also be used rectally in forms of: –– Powder –– Liquid –– Paste –– Tablet 2. Iodine-based contrast media1 are mainly used for visualization of bowel loop during abdominopelvic CT scans for delineating bowel loop from adjacent structures, and examination of the bowel itself. Most commonly used agent is gastrografin®.

Advantages of Oral Computed Tomography Contrast • Adequate distension of bowel by the oral contrast agent helps in easy detection of bowel pathology. • Iso-osmotic contrast agents without orally adminis­ tered positive contrast agents can be used in detection of small bowel obstruction. • For bowel wall enhancement iso-osmotic contrast agents can be used with positive IV contrast.

Rectal Computed Tomography Contrast (Enema) Rectal CT contrast agents are used for visualization of large bowel (colon and rectum). High-attenuation contrast agents (positive): • Barium-based compounds • Iodine-based compounds Low-attenuation contrast agents (negative): • Water • Air

Intravenous Computed Tomography Contrast Media It helps to highlight the vessels and enhance structures like brain, kidney and liver. These contrast agents have water like consistency and are a clear material. Contrast agent is injected intravenously and circulates throughout the body. The tissue, which takes up the contrast, is enhanced and appears white on CT.1

Classification of intravenous CT contrast: • High osmolar contrast media: It contains triiodinated benzene ring with two organic side chains and a carboxyl group. The osmolarity in solution ranges from 600 mOsm/kg to 2,100 mOsm/kg, thus high osmolarity is rated with some adverse effects on its administration. • Low osmolarity contrast: These are of three types: –– Nonionic monomers –– Ionic dimers –– Nonionic dimers 1. Nonionic monomers: In nonionic monomers the tri-iodinated benzene ring is added with hydrophyllic hydroxyl groups to organic side chains making it water soluble.2   At normally used concentrations nonionic monomers range from 290 mOsm/kg to 860 mOsm/kg.

The commonly used are: • Iohexol • Iopamidol • Iopromide 2. Ionic dimers: They are formed by joining two ionic monomers and eliminating one carboxyl group. They contain six iodine atoms for every two particles in solution. It has intermediate osmolarity. • Ioxaglate 3. Nonionic dimer: It is formed by joining two nonionic monomers. It has lowest osmolarity among the low osmolarity agents. These contain six iodine atoms for every one-particle ­ in solution. These can be used as fast bolus injections and high concentration as it is a welltolerated contrast media. Examples are: • Iotrol • Iodixanol.

MAGNETIC RESONANCE IMAGING CONTRAST AGENTS It is the group of contrast media, which is used to improve the internal body structures by increasing the difference between different tissues or between normal and abnormal tissue by altering the relaxation time. Most MRI contrast agents work by shortening the T1 relaxation time of protons inside tissues. Types of MRI contrast agents are:

14  Introduction to Radiology 1. Positive contrast agents: These agents increase signal intensity on T1-weighted image by reducing the T1-relaxation time. 2. Negative contrast agents: These are small particulate aggregate of a term-superparamagnetic iron oxide. They appear predominately dark on MRI. These agents produce shorter T1- and T2-relaxation time by producing “spin-spin” relaxation effects.

Classification of Magnetic Resonance Imaging Contrast Agents • Paramagnetic contrast agents: These are positive contrast agents (T1 enhanced), paramagnetic contrast agents shorten the “spin lattice” relaxation time on T1 and “spin-spin” relaxation time on T2. Shortening of T1 leads to increase signal intensity while shortening T2 produces borderline with decreased intensity,3 the overall result is, thus a nonlinear relationship between signal intensity and the concentration of contrast agents. Paramagnetic contrast agents have unpaired electrons which may be simple substance stable radical or metal ion. “Gadolinium DTPA complex” which is a linear excre­ ting chelate, has a very high formation constant. It had sufficiently favorable properties to be approved by Food and Drug Administration (FDA) of USA.4 • Monocrystalline iron oxide nanocompounds: These are also called “MION”. They are relatively new but rapidly evolving area in MRI contrast agents.5 Brands available in the market are: –– Feridex-active component being ferrous gluconate (300 mg/5 MI) –– Indo remTM—active component being indo­methacin

–– LumiremTM—active component being iron [Mag­netite N-(2-Aminoethyl)-3-Aminopropyl Silylee] –– SineremTM—active component being superpara­ magnetic iron oxide. These are nonstoichiometric microcrystalline mag-­ netite course coated with dextrans or siloxines. These are much more effective in MRI relaxation than paramagnetic contrast. • Metalloporphyrins of iron (iii) and manganese (iii): Porphyrins have been indicators of various matabolic disorders and various diseases since decades. Recently metalloporphyrins have been studied as MRI contrast media due to their low toxicity and their selective retention in tumor. • Native proteins acting as contrast agents: Hemecontaining proteins may act as natural contrast agents due to presence of iron molecules. Uses of blood pool contrast agents: • Cardiac imaging • Magnetic resonance angiography • Venography • Neurological agenesis • Gastrointestinal bleeding • Tumor angiogenesis

REFERENCES 1. Medical Radiology, 2014;273(3):714-8. 2. MC Dickinson Intravascular iodinated contrast media and the anesthetist. Anaesthesia. 2008;6:626-34. 3. Shanglian B, Song G. MRI facility based molecular imaging. Advanced Topics in Science and Technology in China. 2013;333-60. 4. Peter G. Characterisation of brain tissue using dynamic susceptibility contrast MRI. University of Freiburg. 2009; 41-2. 5. Mriconsultant.com

  Role of Contrast  15

MULTIPLE CHOICE QUESTIONS



1. Types of contrast include: a. Positive contrast b. Negative contrast c. Neutral contrast d. Both a and b



2. Which of the following is not a contrast reaction? a. Urticaria b. Anaphylaxis c. Nausea d. Fits



3. Route of contrast administration includes all of the following except: a. Oral b. Intramuscular c. Intravenous d. Enema



4. Gadolinium is a type of: a. Paramagnetic contrast agent b. Monocrystalline iron oxide nanocompound c. Metalloporphyrin d. Diamagnetic



5. Contraindication to contrast includes: a. Unconscious patient b. Deranged renal function c. Dyspepsia d. Young patient



6. Which of the following is not a property of contrast media? a. Osmolarity b. Viscosity c. Toxic d. Miscible



7. All are dose dependent side effects except: a. Metallic taste b. Nausea and vomiting c. Flushing d. Urticarial



8. Which of the following is not used for treatment of pulmonary edema? a. Oxygen mask b. Methyl prednisolone c. Chlorpheniramine d. Hydrocortisone



9. Which is the most common oral contrast agent used: a. Barium sulfate b. Gastrografin c. Gadolinium d. All of the above

10. All of the following are nonionic monomers except: a. Iohexol b. Iopromide c. Iopamidol d. Ioxaglate 11. Which of the following contrast agents are nonionic dimers? a. Iopromide b. Iopamidol c. Ioxaglate d. Iotrol 12. Uses of blood pool contrast agents include all except: a. Cardiac imaging b. Gastrointestinal bleeding c. Tumor angiogenesis d. Splenic infarction 13. Which of the following is not an MRI contrast agent? a. Gadolinium b. Iotrol c. Metalloporphyrins d. Dextrans 14. Triiodinated benzene ring with two organic side chains and a carboxyl group is present in: a. High osmolar media b. Low osmolar media c. Both a and b d. None of the above 15. Spin-spin relaxation effect is produced by: a. Positive contrast agents b. Negative contrast agents c. Both a and b d. None of the above 16. Advantage of oral contrast agents include: a. Adequate distension of bowel by the oral contrast agents helps in easy detection of bowel patho­logy b. Iso-osmotic contrast agents without orally administered positive contrast agents can be used in detection of small bowel obstruction c. For bowel wall enhancement iso-osmotic con­ trast agents can be used with positive IV contrast d. All of the above

16  Introduction to Radiology 17. Drug used for mild anaphylactic reaction is: a. Chlorpheniramine b. Adrenalin c. Gastrografin d. None of the above 18. Metalloporphyrins are used as contrast agents due to: a. High solubility b. High toxicity c. Selective retention in tumor cells d. All of the above

19. Heme proteins act as contrast agents because: a. Presence of copper b. Presence of iron c. Presence of calcium ions d. Presence of magnesium 20. Positive contrast media have: a. High atomic weight b. Low atomic weight c. High solubility d. High osmolality

ANSWERS 1. d 9. a 17. a

2. d 10. d 18. c

3. b 11. d 19. b

4. a 12. d 20. a

5. b 13. b

6. c 14. a

7. d 15. b

8. c 16. d

3 C H A P T E R

Radiation Hazards and Protection

DEFINITION Radiation (electromagnetic radiation) is defined as the form of energy that travels from one place to another without any medium, e.g. heat and light. Ionization is the process of removing an electron from an electrically neutral atom to produce an ion. Radiation is of two types: 1. Ionizing radiation, e.g. alpha rays, beta rays, X-rays, and gamma radiation. 2. Nonionizing radiation, e.g. ultraviolet, visible light, infrared, microwave, radiowaves, and low-frequency radiofrequency (long waves).

REGULATORY BODY Very stern regulation should be framed by a regulatory authority, as there are very bad and adverse effect of electromagnetic radiation seen on human body. Government of India has established Atomic Energy Regulatory Board (AERB) as a regulatory authority, on 15 November 1983.1 This has been approved by President of India, under powers conferred by Section 27 of the Atomic Energy Act of 1962 (33 of 1962). This authority has framed rules and regulation under Atomic Energy Act 1962 and the Environmental (Protection) Act 1986. Main aim behind creating AERB is to protect people of India and keep the environment safe from ionizing radiation and nuclear energy. Thus keeping safe health and environment from hazardous radiation. AERB is headed by a full time Chairperson, an ex officio member and three members who are part time. It has a secretary also to help functioning of this authority. Certain guidelines regarding the specifications of medical X-ray equipment, for the room layout of X-ray installation, regarding the work practices in X-ray department, the protective devices and also the responsibilities of the radiation personnel, employer and

Radiation Safety Officer (RSO) has been laid down by the AERB. Sanction for the new models of X-ray equipment along with the design for any new proposed X-ray installation has been authorized by the AERB. AERB has the following functions additionally: 1. Inspection of new X-ray installations 2. Registration and commissioning new X-ray machine and related equipment. 3. Cancellation of X-ray installation found not following regulation of authority. 4. Certification of service personnel and RSO. 5. It has the power to impose penalties and punishment on persons violating regulations of AERB.

SOURCES OF RADIATION (FIG. 1) • Natural background radiation: –– Cosmic rays –– Gamma rays from earth –– Ingested radioisotopes in certain foods –– Radon decay products (granite) • Artificial background radiation –– Fallout from nuclear explosions –– Radioactive waste • Medical and dental diagnostic radiation • Occupational exposure.

RADIATION HAZARDS • Refers to detrimental effects of radiation on different organs of the body. • Radiation is both useful and hazardous. • Its useful effects being, e.g. diagnosing a disease and management of the malignancy. The degree of radiation hazards depends upon: • Nature of radiation • Type of radiation • Form in which the radiation is received

18  Introduction to Radiology

Fig. 1: Average human radiation exposure per year.

• • • • •

Total dose of radiation Dose rate Part of body exposed to the radiation Age and sex of the person exposed to the radiation Radiation-sensitivity of the organs exposed.

Radiation Units and Conversion Factors (Table 1) Radiation damage to tissue and/or organs depends on the dose of radiation received, or the absorbed dose which is expressed in a unit called the gray (Gy). The potential damage from an absorbed dose depends on the type of radiation and the sensitivity of different tissues and organs. Table 1: Exposure of radiation units and conversion factors. Exposure

Conventional unit SI unit

Exposure

Roentgen (R)

Conversions

Coulomb/kg 1 C/kg = 3.876 R of air (C/kg) 1 R = 258 uC/kg

Dose

Rad (R)

Gray (Gy)

1 Gy = 100 rad

Dose equivalent

Rem

Sievert (Sv)

1 Sv = 100 rem

Activity

Curie (Ci)

Becquerel (Bq)

1 mCi = 37 mBq

Beyond certain thresholds, radiation can impair the functioning of tissues and/or organs and can produce acute (immediate) effects such as skin redness, hair loss, radiation burns, or acute radiation syndrome. These effects are more severe at higher doses and higher dose rates. For instance, the dose threshold for acute radiation syndrome is about 1 Sv (1,000 mSv). If the dose is low or delivered over a long period of time (low dose rate), there is greater likelihood for damaged cells to successfully repair themselves. However, long-term effects may still occur if the cell damage is repaired but incorporates errors, transforming an irradiated cell that still retains its capacity for cell division. This transformation may lead to cancer after years or even decades have passed. Effects of this type will not always occur, but their likelihood is proportional to the radiation dose. This risk is higher for children and adolescents, as they are significantly more sensitive to radiation exposure than adults. Prenatal exposure to ionizing radiation may induce brain damage in fetuses following an acute dose exceeding 100 mSv between weeks 8 and 15 of pregnancy and 200 mSv between weeks 16 and 25 of pregnancy. Before week 8 or after week 25 of pregnancy human studies have not shown radiation risk to fetal brain development. Epidemiological studies indicate that cancer risk after fetal exposure to radiation is similar to the risk after exposure in early childhood (Table 2).

  Radiation Hazards and Protection  19 Table 2: Nuclear regulatory commission (NRC) occupational dose limits. NRC occupational dose limits Whole body (TEDE)

5,000 mrem/yr

Any organ (TODE)

50,000 mrem/yr

Skin (SDE)

50,000 mrem/yr

Extremity (SDE)

50,000 mrem/yr

Lens of eye (LDE)

15,000 mrem/yr

Embryo/Fetus of DPW

500 mrem/yr

Member of the public

100 mrem/yr

Note: 1,000 mrem = 1 rem.

Radiation doses • Conventional CT - 20 mGy • HRCT – 120 Kv, 200 mA, 2 sec –– 4.4 mGy for 1.5 mm at 10 mm intervals (12%) –– 2.1 mGy for 20 mm intervals (6%) –– 36.3 mGy for conventional 10 mm scans at 10 mm intervals • Low dose HRCT at 20 mm interval = chest X-ray.

BIOLOGICAL EFFECTS OF RADIATION (FIG. 2) Whole Body Irradiation “Whole body irradiation” can lead to: • Vomiting • Diarrhea • Loss of weight appetite • Change in blood picture with decrease in blood count. With further increase in dose, death can also result within few days of exposure.

Local Irradiation • Early effects: It includes skin hyperpigmentation, alopecia, ulceration, and excessive redness of the skin. • Late effects: It includes skin atrophy, alopecia, drying of skin, necrosis, and cataract.

Indirect Effects Most of the incident radiation energy is absorbed by the water molecules and these are broken into very unstable and reactive components. These then react with body molecules and cause the cell damage.

Fig. 2: Biological effects of radiation. Source: IAEA World Nuclear Association.

20  Introduction to Radiology Due to generation of H and OH radicals, subsequent to many series of reaction hydrogen peroxide is formed which is highly reactive oxidizing compound and break chemical bonds in macromolecules of body such as proteins, lipids and other nucleic acids, etc. causing cellular damage, cell death, and mutations. The “early effect” of radiation is a result of direct injury to the tissues. Simultaneous and considerable destruction to the radiosensitive cells lead to radiation sickness. These effects appear within days or weeks after exposure and include nausea, vomiting, malaise, diarrhea, fever, hemorrhage, loss of appetite, fall of hair, death, etc. are the dangerous effects of radiation. The “delayed effects” of radiation include shortening of life span, leukemia, malignant tumors, and cataract. These appear after months or even many years of exposure. The biological effects are enhanced by the presence of oxygen which is always present in the cells. Radiation injuries can lead to somatic effects or genetic effects. When the injuries are limited to the single person exposed they are called as somatic effects, e.g. burning sensation in the skin. When the radiation injuries are being transferred over the next generation they lead to genetic effects.

PRINCIPLES OF RADIATION PROTECTION The current radiation protection standards are based on three general principles: 1. Justification of a practice, i.e. no practice involving exposures to radiation should be adopted unless it provides sufficient benefit to offset the detrimental effects of radiation. 2. Protection should be optimized in relation to the magnitude of doses, number of people exposed and also to optimize it for all social and economic strata of patients. 3. Dose limitation, on the other hand, deals with the idea of establishing annual dose limits for occupational exposures, public exposures, and exposures to the embryo and fetus.

Optimization of Protection and the as Low as Reasonably Achievable Principle Optimization of protection can be achieved by optimizing the procedure to administer a radiation dose which

is as low as reasonably achievable (ALARA), so as to derive maximum diagnostic information with minimum discomfort to the patient. ALARA and optimization of radiation protection (ORP) are concepts of the International Commission on Radiological Protection and National Council on Radiation Protection. ORP stands for “optimization of radiation protection”. The history of the ALARA concept is traced back to the Manhattan Project of World War II that radiation exposures are to be kept at lowest possible level. This means that all radiation exposures to patients and personnel are to be kept as low as possible while still obtaining the accurate diagnostic information needed from the procedure. ALARA recognizes that there will always be some radiation exposure to patients involved in radiological procedures using ionizing radiation, but it also recognizes that these exposures can be minimized. Judicious choice of investigations can significantly avoid not only radiation exposures but also increase both the diagnostic accuracy and working efficiency of a radiology department. These include substituting nonionizing methods of examination in place of exami­ nations involving ionizing radiation wherever possible. Some of the methods to reduce radiation exposure, which show the maximum benefits of radiation protection and cause minimum extra costs, are also the simplest. These include avoiding repeat exposures by employing proper exposure factors, and maintaining a proper record of films so that repeat examinations can be avoided wherever possible. “Optimization of Protection” can be achieved by “optimization of the radiological procedure” so as to reduce radiation exposures to the minimum levels. This optimization is possible by good quality assurance and quality control. Factors which can contribute to dose reduction and quality assurance are: the use of high frequency three-phase generator equipment, use of high KV technique and low mAs, using the shortest exposure time, beam collimation, and using proper beam filtration. The other factors which contribute to optimization of procedure are using an X-ray table top which allows high beam transmission, antiscatter grids, high-speed films with rare earth screens, optimal film processing, and largest possible source-to-image receptor distance (SID).

Radiation Protection Actions The triad of radiation protection actions comprise of “time-distance-shielding”. Reduction of exposure

  Radiation Hazards and Protection  21 time, increasing distance from source, and shielding of patients and occupational workers have proven to be of great importance in protecting patients, personnel, and members of the public from the potential risks of radiation.

Exposure Time/Rate The exposure time is related to radiation exposure and exposure rate (exposure per unit time) as follows: Exposure Exposure time = Exposure rate Or Exposure = Exposure rate × Exposure time The algebraic expressions simply imply that if the exposure time is kept short, then the resulting dose to the individual is small.

Distance The second radiation protection action relates to the distance between the source of radiation and the exposed individual. The exposure to the individual decreases inversely as the square of the distance. This is known as the inverse square law, which is stated mathematically as: 1 Ia = 2 d where “I” is the intensity of radiation and “d” is the distance between the radiation source and the exposed individual. For example, when the distance is doubled the exposure is reduced by a factor of four. Another important consideration with respect to distance relates to the SID. The appropriate SIDs for various examinations must always be maintained because an incorrect SID could mean a second exposure to the patient. Long SID results in less divergent beam and thus decreases the concentration of photons in the patients. Short SID results in the reverse action and increases the patient dose. Hence, the longest possible SID should be employed in examinations. However, if a greater than standard SID is used then greater intensity of radiation would be required to produce the same film density which would produce poor quality of image. Therefore, it is recommended that only standard SIDs should be used.

Shielding Shielding implies that certain materials (concrete and lead) will attenuate radiation (reduce its intensity) when

they are placed between the source of radiation and the exposed individual. • X-ray tube shielding • Room shielding –– X-ray equipment room shielding –– Patient waiting room shielding • Personnel shielding • Patient shielding (of organs not under investigation).

X-ray Tube Shielding (Source Shielding) The X-ray tube housing is lined with thin sheets of lead because X-rays produced in the tube are scattered in all directions. This shielding is intended to protect both patients and personnel from leakage radiation. Leakage radiation is that created at the X-ray tube anode but not emitted through the X-ray tube portal. Rather, leakage radiation is transmitted through tube housing. Manufacturers of X-ray devices are required to shield the tube housing so as to limit the leakage radiation exposure rate to an air kerma of 0.88 mGy (corresponding to an exposure of 100 mR) in 1 hour at a distance of 1 m from the X-ray source when measured as specified in the standard. AERB recommends a maximum allowable leakage radiation from tube housing not greater than 1 mGy/h/ 100 cm2.

Room Shielding (Structural Shielding) The lead-lined walls of Radiology Department are referred to as protective barriers because they are designed to protect individuals located outside the X-ray rooms from unwanted radiation There are two types of protective barriers. 1. Primary barrier: It is one which is directly struck by the primary or the useful beam. Primary barriers are built into mammography, CT and fluoroscopy machines and so secondary barrier protection only is usually required in these rooms. In general, a primary barrier is required for: –– Any surface routinely in the direct line of the X-ray beam, including parts of the walls, floor and/ or ceiling (as appropriate) of an X-ray room as well as behind chest stands or wall buckys. The section of the wall, etc. needs to extend at least 300 mm beyond each boundary of the area normally exposed to the primary X-ray beam. –– Acceptable primary barrier—a minimum lead equivalence of 2 mm.

22  Introduction to Radiology 2. Secondary barrier: It is one which is exposed to secondary radiation either by leakage from X-ray tube or by scattered radiation from the patient. Acceptable secondary barrier—general diagnostic room: • 1 mm lead • One sheet of Barytes board (with a lead equivalence of 1 mm at 100 kVp) • Concrete, solid concrete block or concrete block filled with grout or sand, and having a total thickness of not less than 75 mm • For a viewing window lead glass or lead acrylic with 1 mm lead equivalence. For example, double doors: Single-action doors with rebated meeting styles. The shielding of X-ray room is influenced by the nature of occupancy of the adjoining area. In this respect two types of areas have been identified. 1. Control area: It is defined as the area routinely occupied by radiation workers who are exposed to an occupational dose. For control area, the shielding should be such that it reduces exposure in that area to less than 26 mC/kg/week. 2. Uncontrolled areas: These are those areas which are not occupied by occupational workers. For these areas, the shielding should reduce the exposure rate to less than 2.6 mC/kg/week.

Patient Waiting Area Patient waiting areas are provided outside the X-ray room. A suitable warning signal such as red light and a warning placard is provided at a conspicuous place outside the X-ray room and kept “ON” when the unit is in use to warn persons not connected with the particular examination from entering the room.2 Shielding of the X-ray control room: The control room of an X-ray equipment is a secondary protective barrier which has two important aspects: 1. The walls and viewing window of the control booth, which should have lead equivalents of 1.5 mm. 2. The location of control booth, which should not be located where the primary beam falls directly, and the radiation should be scattered twice before entering the booth. The AERB recommends the following shielding for the X-ray control room: The control panel of diagnostic X-ray equipment operating at 125 kVp or above is installed in a separate room located outside but contiguous to the X-ray

room and provided with appropriate shielding, direct viewing and oral communication facilities between the operator and the patient.

Personnel Shielding Shielding of occupational workers can be achieved by following methods: • Personnel should remain in the radiation environment only when necessary (step behind the control booth, or leave the room when practical). • The distance between the personnel and the patient should be maximized when practical as the intensity of radiation decreases as the square of distance (inverse square law). • Shielding apparel should be used as and when necessary which comprise of lead aprons, eye glasses with side shields, hand gloves, and thyroid shields. Lead aprons are shielding apparel recommended for use by radiation workers. These are classified as a secondary barrier to the effects of ionizing radiation. These aprons protect an individual only from secondary (scattered) radiation, not the primary beam. The thickness of lead in the protective apparel determines the protection it provides. Other protective apparel includes eye glasses with side shields, thyroid shields and hand gloves. The minimum protective lead equivalents in hand gloves and thyroid shields should be 0.5 mm.

RADIATION PROTECTION • Ionizing radiations are potentially harmful, therefore effective protective measures should be taken so that the harmful effect is less as compared to the benefits. • For this it is important to make sure that the radiation dose which the patient receives is minimum as required for the necessary information. • The amount of scattered radiation depends upon the dose of the radiation, energy of the incident beam and the area irradiated. • The major source of excess radiation to the radiographer and the patient is repeat radiograph so it should be avoided as much as possible • The organs that are not under examination should be protected, especially genitals • In pregnancy, X-rays should be done only when absolu­tely indicated.

  Radiation Hazards and Protection  23

Protection for the Radiologist and Radiographer • Never come across in the direct beam and be as much away from all radiation sources • Use smallest possible X-ray beams to reduce radiation to the radiographer • As intensity of radiation varies inversely as the square of the distance therefore increase the distance between the sources of radiation and are under examination • Radiographer should wear lead aprons and should stand behind lead-lined protective screens • Lead glass and lead gloves should be worn by the radiologist • Radiologist should sit in the dark room, should close his eyes for some time prior to fluoroscopy to prevent unnecessary radiation exposure during fluoroscopy • Reduce the duration of exposure • The work should be completed quickly and by sharing with other people • Use the film badge which will help in continuously updating the personal record of all the workers • These film badges are being sent to Bhabha Atomic Research Centre (BARC) Bombay (Mumbai) for assessing the radiation dose received by the person

• If the person has been exposed to more than permissible limits he is immediately shifted from the radiation field until the dose level comes within the permissible limits.

X-ray Film Badges These badges use small X-ray films sandwiched between several filters to help detect radiation. Film badges are inexpensive, easy to use, and easy to process. Although they are useful for detecting radiation at or above 0.1 mSv (10 mrem), they are not sensitive enough to capture lower levels of radiation. Their susceptibility to fogging caused by high temperatures and light means that they cannot and should not be worn for longer than a 4-week period at a stretch. Another major drawback to film badge monitoring is that it is an enormous task to chemically process a large number of small films and subsequently compare each to some standard test film. In India, film badges have recently been replaced by thermoluminescent dosimeter (TLD) badges (Fig. 3). The limitations of the film badge are overcome by the TLD. Thermoluminescence is the property of certain materials to emit light when they are stimulated by heat. Materials such as lithium fluoride (LiF), lithium borate

Fig. 3: Thermoluminescent dosimeter (TLD) badge.

24  Introduction to Radiology (Li2B4O7), calcium fluoride (CaF2), and calcium sulfate (CaSO4)3 have been used to make TLDs. When an LiF crystal is exposed to radiation, a few electrons become trapped in higher energy levels. For these electrons to return to their normal energy levels, the LiF crystal must be heated. As the electrons return to their stable state, light is emitted because of the energy difference between two orbital levels. The amount of light emitted is measured (by a photomultiplier tube) and it is proportional to the radiation dose. The measurement of radiation from a TLD is a two-step procedure. In step 1, the TLD is exposed to the radiation. In step 2, the LiF crystal is placed in a TLD analyzer, where it is exposed to heat. As the crystal is exposed to increasing temperatures, light is emitted. When the intensity of light is plotted as a function of the temperature, a glow curve results. The glow curve can be used to find out how much radiation energy is received by the crystal because the highest peak and the area under the curve are proportional to the energy of the radiation. These parameters can be measured and converted to dose. Whereas the TLD can measure exposures to individuals as low as 1.3 µC/kg (5 mR), the pocket dosimeter can measure up to 50 µC/kg (200 mR). The film badge, however, cannot measure exposures less than 2.6 µC/ kg (10 mR). TLDs can withstand a certain degree of heat, humidity, and pressure; their crystals are reusable; and instantaneous readings are possible if the department has a TLD analyzer. The greatest disadvantage of a TLD is its cost. • Use of TLD badge: It comprises of CaSO4 that is thermoluminescent material activated with dys­­pro­sium. • Thermoluminescent phenomenon helps in getting light emission from preirradiated thermoluminescent material. • Thermoluminescent dosimeter badge comprises of a plastic cassette and nickel-plated aluminium containing three TLD disks placed over circular holes. • Thermoluminescent dosimeter disks are sensitive to X-rays, gamma rays, and beta rays and these radiation doses are calculated on the basis of differential filtration on the disks.

• Thermoluminescent dosimeter badge is conducted on quarterly basis and sent to BARC Bombay (Mumbai) for radiation dose evaluation.

Protection for the Patient • Use fluoroscopy over X-rays only if absolutely indicated • Image intensifiers are being used as it imparts safety from the radiation and much better appreciation of the organ under examination • Use of X-ray beam restrictors like diaphragms and cones so that the part to be examined is only irradiated • Patient should be positioned correctly and proper exposure factors should be used • Use of lead rubber over gonads in order to protect them • Pelvis radiography should be avoided in pregnant females • Repeating of X-rays should be avoided as much as possible in pregnancy • For radiographing the thicker body parts kilovoltage should be increased to minimize the dose to the skin • Grid should be used.

X-ray in Young Female Patients of Reproductive Age “10-day rule”2 was postulated by the International Commission on Radiological Protection for woman of reproductive age. It states that “whenever possible, one should confine the radiological examination of the lower abdomen and pelvis to the 10-day interval following the onset of menstruation”. The original proposal was for 14 days, but this was reduced to 10 days to account for the variability of the human menstrual cycle.

REFERENCES 1. [Internet]. 2017 [cited 21 June 2017]. Available from: http://www.aerb.gov.in/AERBPortal/pages/English/t/ annrpt/2015/annrpt2k15.pdf 2. McCollough CH, Schueler BA, Atwell TD, et al. Radiation Exposure and Pregnancy: When should we be concerned? 1. Radiographics. 2007;27(4):909-17. 3. Vohra KG, Bhatt RC, Chandra B, et al. A personnel dosi­ meter TLD badge based on CaSO4: Dy Teflon TLD Discs. Health physics. 1980;38(2):193-7.

  Radiation Hazards and Protection  25

MULTIPLE CHOICE QUESTIONS





1. AERB means: a. American Energy Regulatory Board b. Atomic Energy Restriction Board c. Atomic Energy Regulatory Board d. None 2. Sources of radiation: a. Cosmic rays, gamma rays from earth, ingested radioisotopes in certain foods, radon decay products (granite) b. Medical and dental diagnostic radiation c. Occupational exposure d. All of the above



3. Unit of absorbed radiation: a. Radon b. Gray c. Coulomb d. Curie



4. Radiation hazards: a. Infertility b. Skin changes such as hyperpigmentation, dryness, atrophy c. Cancer/Carcinoma d. All of the above







5. Radiation protection measures include: a. Exposure time b. Shielding c. Distance between source and exposed individual d. All of the above 6. Dose radiation for acute radiation syndrome: a. 1,000 mSv b. 900 mSv c. 800 mSv d. 1,100 mSv 7. Brain damage can occur in fetuses of gestational age: a. 7–20 weeks b. 8–25 weeks c. 8–20 weeks d. 6–18 weeks

c. As light as reasonably achievable d. All American Radiation Association 10. ORP means: a. Optimization of Radiation Protection b. Oxidation-Reduction Potential c. Objective Rally Point d. Optional Retirement Program 11. Factors contributing to dose reduction and quality assurance: a. Use of high frequency three-phase generator equipment b. Using proper beam filtration c. Use of high KV technique and low mAs d. All of the above 12. Triad of radiation protection actions comprise of: a. Time-distance-shielding b. Time-distance-exposure unit c. Distance-time-speed d. Time-distance-number of persons 13. SID means: a. Source-to-image receptor distance b. Society for information display c. Saab information display d. Society for investigative dermatology 14. Materials that attenuate radiation: a. Iron b. Aluminum c. Copper d. Lead 15. Where is leakage radiation created? a. X-ray tube anode b. X-ray tube cathode c. X-ray tube portal d. X-ray tube



8. Biological effects of radiation exposure are enhanced by presence of: a. Oxygen b. Hydrogen c. Nitrogen d. Fluoride

16. Maximum allowable leakage radiation from tube housing recommended by AERB: a. 3 mGy/hour/100 cm2 b. 2 mGy/ hour/100 cm2 c. 5 mGy/hour/100 cm2 d. 1 mGy/ hour/ 100 cm2



9. ALARA means: a. As low as recently achievable b. As low as reasonably achievable

17. The radiation exposure in control area should be: a. vermis)

Pleomorphic xanthoastrocytoma

Adolescent

Temporal > frontal > parietal

Subependymal giant cell astrocytoma

50 years

Cerebral hemisphere white matter

Fig. 31: Subependymal giant cell astrocytoma (SEGA).

Fig. 32: Magnetic resonance imaging (MRI) T2-weighted image (T2WI) showing SOL with heterogeneous intensity involving frontal lobe.

Types • Ependymoma: –– Site: Fourth ventricle –– MRI: Solid components are hypointense or iso­intense on T1WI and hyperintense on T2WI, moderate inhomogenous postcontrast enhance­ ment is seen. • Subependymoma: Rare, middle age group is affected –– Site: Arises from lower medulla and extends into fourth ventricle, frontal horn of lateral ventricle –– MRI: Hypo- to isointense on T1WI, hyperintense on T2WI; postcontrast enhancement is not seen.

Choroid Plexus Tumors (Fig. 34) Fig. 33: Magnetic resonance imaging (MRI) T1-weighted image (T1WI) showing isointense SOL involving fourth ventricle.

• Age group: Less than 5 years, more common in adults.

156  Magnetic Resonance Imaging • Site: Trigone of lateral ventricle, fourth ventricle (in adults). • MRI: Large well-delineated lobulated mass isointense on T1WI and iso- to hyperintense on T2WI; and postcontrast enhancement is seen.

REFERENCES 1. ten Donkelaar HJ, Lammens M, Wesseling P, et al. Development and developmental disorders of the human cerebellum. J Neurol. 2003;250(9):1025-36. 2. Leite CC, Lucato LT, Santos GT, et al. Imaging of adult leukodystrophies. Arq Neuropsiquiatr. 2014;72(8):625-32.

Fig. 34: Magnetic resonance image (MRI) shows large lobulated mass arising from choroid plexus.

MULTIPLE CHOICE QUESTIONS









1. All brain tumor shows postcontrast enhancement except: a. Low grade glioma b. Hemangioblastoma c. Choroid plexus papilloma/carcinoma d. Ependymoma 2. Type II Arnold-Chiari malformation is associated with: a. Meningocele b. Meningomyelocele c. Nerve tube defect d. All of the above 3. Dural cleft sign is seen in: a. Extra-axial tumors b. Intra-axial tumors c. Both a and b d. None 4. Physiological calcification is seen in all except: a. Choroid plexus b. Pacchionian granules c. Basal ganglia d. Choroid plexus papiloma 5. Posterior fossa malformations include all except: a. Arnold-Chiari malformation b. Dandy-Walker malformation

c. Giant cistern magna d. None

6. Causative organism for encephalitis is: a. Herpes simplex virus (HSV) b. Toxoplasma gondii c. Both a and b d. None



7. “Dawson fingers” are seen in: a. Multiple sclerosis b. Encephalitis c. Meningitis d. None



8. Which of the following is/are demyelination disease/s? a. Alexander disease b. Canavan’s disease c. Both a and b d. None



9. Subdural hemorrhage is located between: a. Dura mater and arachnoid layer b. Pia mater and arachnoid layer c. Both a and b d. None

10. Thunderclap headache is seen in: a. Subarachnoid hemorrhage b. Subdural hemorrhage c. Extradural hemorrhage d. All of the above

  Basic Magnetic Resonance Imaging Pathologies  157 11. Oligodendrogliomas are ________ on T2WI. a. Hyperintense b. Hypointense c. Isointense d. None

12. Choroid plexus tumors are: a. Isointense on T2WI b. Hypointense on T2WI c. Both a and b d. None

ANSWERS 1. a 9. a

2. d 10. a

3. a 11. a

4. d 12. a

5. d

6. c

7. a

8. c

HEPATOBILIARY SYSTEM

LIVER Introduction Liver is the largest gland in the body weighing about 1.4 kg in an adult. It occupies the right hypochondrium and a part of the epigastrium. It has two major surfaces: (1) a superior or diaphragmatic surface and (2) an inferior visceral surface. At the porta hepatis the hepatic artery, the main portal vein, and the common bile duct (CBD)

A

are contained within investing peritoneal folds known as hepatoduodenal ligament. Bismuth and Couinaud classified liver anatomy which divides the liver into four sectors and eight functionally independent segments based on hepatic vein and branches of portal vein. In the center of each segment, there is a branch of portal vein, hepatic artery and bile duct (Figs. 35 and 36).

B

Figs. 35A and B: Classification of liver anatomy: four divisions.

158  Magnetic Resonance Imaging

Fig. 36: Magnetic resonance imaging (MRI) showing segments of liver on axial scan.

Fig. 38: Magnetic resonance imaging (MRI) section T1-weighted image shows a hypointense cystic space occupying lesions (SOL) in liver.

Magnetic Resonance Imaging Liver parenchyma appears homogenous on both T1 and T2 images. Liver shows moderate signal intensity on T1-weighted images (T1WIs). Bile appears hyperintense on T2WI (Fig. 37).

Fig. 37: Magnetic resonance imaging techniques sequences.

Hepatic cysts: Simple hepatic cysts are common benign liver lesions and have no malignant potential. They can be diagnosed on ultrasound, CT or MRI. • Epidemiology: Simple hepatic cysts are one of the most common liver lesions, occurring in approximately 2–7% of the population. There may be a slight female predilection. • Clinical presentation: Hepatic cysts are typically discovered incidentally and are almost always asymptomatic. • Location: While they can occur anywhere in the liver, there may be a greater predilection toward the right lobe of the liver. • Associations: Certain diseases are associated with multiple hepatic cysts and include: –– Polycystic liver disease –– Autosomal dominant polycystic kidney disease (ADPKD): Hepatic cysts may be seen in approxi­ mately 40% of those with ADPKD.

Benign Lesions

Hemangioma: Hepatic hemangiomas (also known as hepatic venous malformations) are benign non-neoplastic hypervascular lesions. They are frequently diagnosed as an incidental finding on imaging and most patients are asymptomatic (Figs. 40 to 42).

• Hepatic cysts/polycystic disease • Hemangioma • Lipoma • Abscess.

Typical features include: • T1: Hypointense relative to liver parenchyma • T2: Hyperintense relative to liver parenchyma, but less than the intensity of CSF or of a hepatic cyst

Focal Liver Lesions1 (Figs. 38 and 39)

  Basic Magnetic Resonance Imaging Pathologies  159

A

B Figs. 39A and B: Magnetic resonance imaging (MRI) axial section (T1 and T2) shows cyst hypointense and hyperintense respectively (arrows).

Fig. 40: Magnetic resonance imaging (MRI) axial section T1, T2, and T1*C-weighted images show hypointense SOL on T1 and hyperintense on T2 with homogenous enhancement on contrast administration.

A Fig. 41: Magnetic resonance imaging (MRI) axial section shows hyperintense lesion on T2.

B

Figs. 42A and B: Case 1, MRI image showing hypointense lesion on T1- and hyperintense on T2-weighted sequences, besides target enhance­ment.

160  Magnetic Resonance Imaging • T1 C + (Gd): Often shows peripheral nodular dis­conti­ nuous enhancement which progresses centripetally (inward) on delayed images –– Hemangiomas tend to retain contrast on delayed (>5 minutes) contrast-enhanced images –– Atypical hemangiomas may demonstrate slightly altered enhancement patterns. • T1 C + (hepatobiliary contrast): In general, delayed imaging with Eovist/Gd-BOPTA may not be helpful, since hemangiomas can have a variable appearance that ranges from hypointensity to diffuse and central enhancement • DWI: Hemangiomas appear hyperintense on [diffu­ sion-weighted imaging (DWI)] due to T2 shine-through rather than restricted diffusion. Abscess: It can be bacterial or amebic. These are localized collections of necrotic inflammatory tissue caused by bacterial, parasitic or fungal agents. • Epidemiology: –– In developing countries parasitic abscesses are most common. –– In developed countries liver abscesses are rare in healthy individuals, with imported infections from visits overseas accounting for the majority of cases. • Clinical presentation: Right upper quadrant pain, fever, and jaundice. Anorexia, malaise, and weight loss are also frequently seen.

Bacterial Abscess • T1: –– Usually hypointense centrally –– Heterogeneous –– May be slightly hyperintense in fungal abscess • T2: Tends to have hyperintense signal • T1 + C (Gd): –– Enhancement of the capsule, although this may be absent in immunocompromised patients –– Multiple septations may be visible. Amebic: On T1 the contrast cavity is usually of decreased signal intensity relative to liver and has increased signal intensity on T2. After administration of GD-DTPA, the hyperemic reactive zone demonstrates enhancement.

Malignant Lesions Hepatocellular carcinoma: It is the most common primary malignancy of the liver. It is strongly associated with cirrhosis, from both alcohol and viral etiologies.

Epidemiology: Hepatocellular carcinoma (HCC) is the fifth most common cancer in the world and is the third most common cause of cancer-related death after lung and stomach. The highest prevalence is in Asia. In Western countries, the rate is lower and alcohol accounts for a greater proportion of cases. Risk factors include: • Hepatitis B (HBV) infection • Hepatitis C (HCV) infection • Alcoholism • Biliary cirrhosis • Food toxins, e.g. aflatoxins • Congenital biliary atresia • Inborn errors of metabolism –– Hemochromatosis –– Alpha-1 antitrypsin deficiency –– Type 1 glycogen storage disease –– Wilson disease. Clinical presentation: • Constitutional symptoms • Jaundice • Portal hypertension from invasion of the portal vein • Hepatomegaly/mass. Imaging (MRI): When seen in the setting of cirrhosis, small HCCs need to be distinguished from regenerative and dysplastic nodules. • T1: –– Variable –– Iso- or hyperintense –– Hyperintensity may be due to: ◆◆ Intratumoral fat ◆◆ Decreased intensity in surrounding liver • T1 C+ (Gd): –– Enhancement is usually arterial (hypervascu­larity) –– Rapid “washout”, becoming hypointense cf. remain­ der of the liver (96% specific) (Figs. 43 and 44) ◆◆ This is because the supply to HCCs is pre­­ dominantly from the hepatic artery rather than portal vein –– Rim enhancement may persist (referred to as a capsule) • T2: Variable, typically moderately hyperintense.

Diffuse Liver Disease Fatty Liver It refers to excessive accumulation of triglycerides in the form of small or large vacuoles within the hepatocytes.

  Basic Magnetic Resonance Imaging Pathologies  161

A

B Figs. 43A and B: Magnetic resonance image (MRI) axial sections show hypointense lesion on T1, hyperintense on T2 with rapid washout.

A

B

C

D

Figs. 44A to D: T1- and T2-weighted images showing heterogeneous SOL with mixed areas of signal intensities.

Causes • Malnutrition • Drugs and toxins • Total parenteral nutrition

• Inflammatory bowel disease (IBD) • Alcoholism • Severe diabetes mellitus • Hepatitis.

162  Magnetic Resonance Imaging

A

B

Fig. 45: Magnetic resonance imaging (MRI) axial section shows hyperintense signals involving diffuse liver parenchyma on T1weighted image indicating fatty changes.

Figs. 46A and B: Magnetic resonance image (MRI) coronal and axial sections show regenerating nodules with greater sensitivity that appear hypointense on T1-weighted images.

On magnetic resonance imaging: Fatty liver may demon­ strate increased signal intensity of liver on T1- and T2-weighted images (Fig. 45).

PANCREAS2

Cirrhosis

Normal pancreas is a sharply defined homogenously enhancing organ with smooth or slightly lobulated outline. It is obliquely placed with the tail higher at splenic hilum and head is lower and surrounded by C-shaped duodenal loop (Fig. 47).

Chronic disease of liver characterized by fibrosis and nodular regeneration of liver in response to hepatocellular necrosis. • Etiology: –– Alcohol abuse –– Nonalcoholic fatty liver disease (NAFLD), which is associated with: ◆◆ Insulin resistance/diabetes mellitus ◆◆ Obesity ◆◆ Dyslipidemia –– Exogenous steroid intake –– Drugs (amiodarone, methotrexate, and chemo­ therapy) –– Intravenous hyperalimentation –– Chronic hepatitis –– Pregnancy: Acute fatty liver of pregnancy (AFLP) –– Metabolic disorders ◆◆ Glycogen storage diseases –– Radiation. • Imaging –– T1: Hyperintense –– T2: Mildly hyperintense. It can also demonstrate regenerating nodules with greater sensitivity that appears hypointense on T1- and T2-weighted images and occasionally hyperintense on T1-weighted images (Figs. 46A and B).

Introduction

Size • Head: 3–4 cm • Body: 2–3 cm • Tail: 1–2 cm. Pancreatitis: Referred as inflammation of pancreas. • Types: –– Acute pancreatitis –– Chronic pancreatitis

Acute Pancreatitis It is defined as acute, diffuse inflammatory process of pancreas that exhibit great variation in the degree of involvement of gland and is a potentially life-threatening condition. • Causes: –– Gallstones –– Alcohol abuse –– Less commonly—hypertriglyceridemia –– Hypercalcemia –– Medication.

  Basic Magnetic Resonance Imaging Pathologies  163

A

B

Figs. 48A and B: Magnetic resonance imaging (MRI) axial sections show T1- and T2-weighted images showing pseudocyst formation appearing hypointense on T1 and hyperintense on T2 (*).

Fig. 47: Normal pancreas.

• Classical clinical features include: –– Acute onset of severe central epigastric pain (over 30–60 minutes) –– Poorly localized tenderness and pain –– Exacerbated by supine positioning –– Radiates through to the back in 50% of patients. Elevation of amylase and lipase are 90–95% specific for the diagnosis. Signs of hemorrhage include: • Cullen sign: Periumbilical bruising • Grey-Turner’s sign: Flank bruising. Magnetic resonance imaging can detect many mor­­ phological changes from acute pancreatitis and can be used as an adjunct in patients who cannot receive contrast media because of allergy or renal insufficiency. T1 images are useful to depict pancreatic and peripancreatic edema and also T2 depicts fluid collections, pseudocyst formation and hemorrhage that appears bright on T2-weighted images (Figs. 48A and B).

Chronic Pancreatitis Chronic pancreatitis represents the end result of a continuous, prolonged, inflammatory, and fibrosing process that affects the pancreas. This results in irreversible morphologic changes and permanent endocrine and exocrine pancreatic dysfunction (Figs. 49A and B). Epidemiology: The most common cause of chronic pancreatitis in adults is excessive alcohol consumption

A

B

Figs. 49A and B: Magnetic resonance imaging (MRI) axial scan shows walled off collection which appears dark on T1- and bright on T2-weighted images suggesting chronic pancreatitis (*).

in developed countries and malnutrition in developing countries. Clinical presentation: Patients may present with exacer­ bations (episodes of acute pancreatitis) manifesting as epigastric pain, which may recur over a number of years. • Causes: Long-standing alcohol abuse is the most common cause. • Others: –– Chronic biliary tract disease –– Hereditary pancreatitis –– Cystic fibrosis –– Hyperparathyroidism. Magnetic resonance image findings: The pancreas may show diminished signal intensity of parenchyma and less intense, heterogeneous, glandular enhancement than normal on T1-weighted images.

Pancreatic Tumors (Figs. 50 and 51) There are numerous primary pancreatic neoplasms, in part due to the mixed endocrine and exocrine components. • Mainly involves middle and elderly age • Males >> females

164  Magnetic Resonance Imaging

Fig. 50: Magnetic resonance imaging (MRI) axial scan shows hyper­ intense lesion involving tail region on T2-weighted image suggesting mucinous cystadenoma of pancreas (arrow).

Risk Factors • Alcohol • High intake of animal fat in diet • Smoking • Hereditary pancreatitis.

Classification • Exocrine: Approximately 99% of all primary pancreatic neoplasms –– Pancreatic ductal adenocarcinoma approximately 90–95% –– Cystic neoplasm –– Intraductal papillary mucinous neoplasm (IPMN) • Endocrine: Tumors originate from pluripotential stem cells in ductal epithelium –– Nonfunctional –– Functional • Mesenchymal tumors: It can derive from the connective, lymphatic, vascular, and neuronal tissues of the pancreas.

Magnetic Resonance Imaging Pancreatic tumors being desmoplastic in nature are usually hypointense to normal parenchyma on T1 fat saturated and nonfat saturated images. • Magnetic resonance imaging: –– T1: Hypointense to normal pancreas –– T2/FLAIR: Variable—depending on the amount of reactive desmoplastic reaction

Fig. 51: Magnetic resonance imaging (MRI) axial section shows mass lesion involving head of the pancreas showing decreased signal intensity on T1-weighted image suggesting ductal carcinoma (arrow).

–– T1 + C (Gd): Slower enhancement than normal pancreas, therefore dynamic injection with arterial phase imaging with fat saturation is ideal –– Magnetic resonance cholangiopancreatography (MRCP): Double duct sign may be seen.

SPLEEN Introduction It is a wedge-shaped organ lying in the left hypochondrium and partly in epigastrium. It is soft, highly vascular organ and is related to 9–11 ribs anatomically (Fig. 52).

Magnetic Resonance Imaging Spleen shows a lower signal on T1- and higher signal on T2-weighted images because of its greater blood volume. The greater perfusion of spleen is illustrated by intense early enhancement after contrast administration.

Causes of Splenomegaly (Figs. 53A and B) • Lymphomas • Malaria • Leishmaniasis • Myeloproliferative disorders • Gaucher’s disease • Neimann-Pick disease • Cysts • Trauma.

  Basic Magnetic Resonance Imaging Pathologies  165

Fig. 52: Coronal MRI showing wedged shaped spleen (letter “S”), liver (letter “L”).

A

B

Figs. 53A and B: Magnetic resonance imaging (MRI) axial and coronal sections show splenomegaly [star (*)].

COMMON BILE DUCT (FIGS. 54 AND 55) Introduction

• Majority of bile calculi are secondary caculi that originate in gallbladder and then migrate via the cystic duct or through cholecystocholedochal fistula.

Common bile duct measures up to 8 mm in adults in asymptomatic patients with normal liver function. Magnetic resonance cholangiopancreatography is a noninvasive technique for evaluation of biliary tree and its pathologies.

Epidemiology

Choledocholithiasis

Stones within the bile duct are often asymptomatic and may be found incidentally, however more frequently they lead to symptomatic presentation with: • Biliary colic • Ascending cholangitis • Obstructive jaundice • Acute pancreatitis

• Calculus in bile duct is termed as choledocholithiasis. • Choledocholithiasis denotes the presence of gallstones within the bile ducts (common hepatic duct/common bile duct).

Choledocholithiasis is relatively common, seen in 6–12% of patients who undergo cholecystectomy.

Clinical Presentation

166  Magnetic Resonance Imaging

A Fig. 54: Magnetic resonance cholangiopancreatography (MRCP) shows multiple hypointense filling defects in common bile duct suggesting caculi.

A

B

Figs. 55A and B: Magnetic resonance imaging (MRI) reveals calculi as a low signal intensity filling defect in biliary tract.

B Figs. 56A and B: Magnetic resonance imaging (MRI) axial sections show multiple small hypointense filing defects in gallbladder indicating calculi.

Imaging

Clinical Presentation

Magnetic resonance imaging is capable of diagnosing even very tiny calculus as small as 2 mm. Apart from this, benign strictures, pancreatitis, gallstones can also be visualized.

Cholelithiasis may be symptomatic in only 25% of cases. The most common presentation is right upper quadrant or epigastric abdominal pain or discomfort especially after a fat-rich meal. Other symptoms include: belching, bloating, flatulence, heartburn, and nausea. Abdominal pain is often referred to shoulder. Patients may demonstrate this radiation to the tip of scapula by placing their hands behind the back and thumb pointing upward—“Collins’ sign”.

GALLBLADDER Cholelithiasis3 Cholelithiasis is the presence of calculus within the gallbladder (Figs. 56A and B).

  Basic Magnetic Resonance Imaging Pathologies  167

A

B

C

Figs. 57A to C: Magnetic resonance imaging (MRI) axial and coronal sections show heterogeneous hypointense soft tissue mass in distended gallbladder with proximal intrahepatic biliary radical dilatation indicating carcinoma gallbladder.

Gallbladder Carcinoma (Figs. 57A to C)

Pathology

Gallbladder adenocarcinoma is the most common primary biliary. Predominantly affects older persons with longstanding cholecystolithiasis, and as such is most common in elderly women (>60 years of age, F:M ratio 4:1).

Over 90% of cases of gallbladder cancer are adeno­ carcinomas. Squamous cell carcinoma is account for the majority of the remainder.



Risk factors include:

• Chronic cholecystitis: Gallstones are seen in 70–90% of cases. • Familial adenomatous polyposis syndrome (FAP) • Inflammatory bowel disease (IBD) • Porcelain gallbladder.

Clinical Presentation Patients are invariably asymptomatic, and as such a therapeutic window is usually missed. Eventually symptoms develop, at which time the mass is usually not resectable. Clinical presentation depends on the direction in which the mass extends. In cases where biliary obstruction is created then jaundice is often the first presentation. If the malignancy is located in the body or fundus of the gallbladder then extension into the liver or adjacent colon or small bowel can lead to local pain or bowel obstruction respectively. Other symptoms include right upper quadrant pain, weight loss and anorexia.

Imaging Magnetic resonance imaging is useful in characterization of the malignant lesions and is useful in staging of tumor. Gallbladder carcinoma appears as focal or diffuse mural thickening or irregularity or a mass replacing the entire normal gallbladder fossa or as a polypoidal mass or its combination. • Lesions are hypointense on T1 and heterogeneously hyper on T2. • Early enhancement after dynamic contrast adminis­tration.

PORTAL VEIN4 (FIGS. 58 AND 59) Introduction The normal portal vein pressure is 6–10 mm Hg or gradient of less than 5 mm Hg between hepatic and portal. Anything beyond this limit is termed as portal hypertension.

Causes of Portal Hypertension • Presinusoidal: –– Portal vein thrombosis –– Extrinsic compression of portal vein –– Schistosomiasis (Schistosoma mansoni Schistosoma japonicum)

or

168  Magnetic Resonance Imaging

Fig. 58: Magnetic resonance imaging (MRI) axial scan shows small nodular liver because of cirrhosis of liver with ascites and enlarged spleen due to portal hypertension.

• Sinusoidal –– Cirrhosis • Postsinusoidal –– Budd-Chiari syndrome –– Hepatic veno-occlusive disease –– Right heart failure or biventricular cardiac failure.

Imaging Findings • Dilated portal vein ± mesenteric veins • Contrast enhancement of paraumbilical vein: Pathognomonic • Collateral vessels/varices –– Coronary venous collaterals: Considered one of the most common –– Esophageal collaterals –– Paraumbilical collaterals –– Abdominal wall collaterals –– Perisplenic collaterals –– Mesenteric collaterals –– Splenorenal collaterals

Fig. 59: Magnetic resonance imaging (MRI) axial scan shows ascites with splenomegaly due to portal hypertension.

• Ascites • Splenomegaly.

Magnetic Resonance Imaging • Portal hypertensive patients usually present with ascites but magnetic resonance imaging is not hindered by ascites or obesity. • On routine MRI portal vein and variceal collaterals appears as signal free structures owing to flow voids.

REFERENCES 1. Mortelé KJ, Ros PR. Cystic focal liver lesions in the adult: differential CT and MR imaging features. Radiographics. 2001;21(4):895-910. 2. Krige JE, Beckingham IJ. ABC of diseases of liver, pancreas, and biliary system: Liver abscesses and hydatid disease BMJ. 2001;322(7285):537-40. 3. Shaffer EA. Gallstone disease: Epidemiology of gallbladder stone disease. Best Pract Res Clin Gastroenterol. 2006; 20(6):981-96. 4. Syed MA, Kim TK, Jang HJ. Portal and hepatic vein throm­ bosis in liver abscess: CT findings. Eur J Radiol. 2007; 61(3):513-9.

  Basic Magnetic Resonance Imaging Pathologies  169

MULTIPLE CHOICE QUESTIONS













1. Which of the following answer choices about the common uses of the ultrasound is false? a. Detect disorders within the prostate b. Determine whether the prostate is enlarged, with measurements acquired as needed for any treatment planning c. Detect an abnormal growth within the prostate d. Help diagnose the cause of a man’s infertility 2. FDG-PET scanning appears to be of greatest value in evaluating patients with prostate cancer in assessing what situation? a. Localized disease b. Regional node metastases c. Bone metastases d. Response to therapy 3. Double duct sign seen in: a. Hepatocellular carcinoma b. Intrahepatic abscess c. Gallbladder carcinoma d. Periampullary carcinoma



7. Causes of massive splenomegaly are: a. Malaria b. Kala-azar c. Both a and b d. None



8. Disease associated with multiple hepatic cysts is: a. Autosomal dominant polycystic kidney disease b. Malaria c. Myeloproliferative disorders d. None



9. Liver in adult weights approximately: a. 5 kg b. 500 g c. 1.4 kg d. None

10. Which of the following inborn errors of metabolism is associated with HCC? a. Albinism b. Dandy-Walker syndrome c. Alpha-1 antitrypsin deficiency d. None 11. Spleen is anatomically related to: a. 4–6th ribs b. Floating ribs c. 9–11th ribs d. None

4. Magnetic resonance cholangiopancreatography (MRCP) is: a. T1-weighted sequence b. T2-weighted sequence c. Heavily T2-weighted sequence d. Fat suppressed sequence 5. Filling defect in T2 sequence on MRCP indicates: a. Fluid b. Fat c. Calculus d. None 6. Choledocholithiasis is: a. Calculus in gallbladder b. Calculus in cystic duct c. Calculus in common bile duct d. Calculus in pancreatic duct

12. Collin’s sign is seen in: a. Cholelithiasis b. Choledocholithiasis c. HCC d. Gallbladder carcinoma 13. MRCP is a technique for evaluation of: a. Pancreas b. Spleen c. Biliary tree d. Liver cysts 14. MRCP stands for: a. Magnetic resonance cholangiopancreatography b. Magnetic resonance choledochoplasty c. Magnetic resonance cholangioplasty d. None 15. Normal portal vein pressure is: a. 50–70 mm Hg b. 6–10 mm Hg c. 1–3 mm Hg d. None

ANSWERS 1. c 9. c

2. b 10. c

3. d 11. c

4. c 12. a

5. c 13. c

6. c 14. a

7. c 15. b

8. a

170  Magnetic Resonance Imaging

MAGNETIC RESONANCE IMAGING THORAX

INTRODUCTION • Magnetic resonance imaging (MRI) evolved as a third lung imaging modality, combining morphological and functional information. Unlike a computed tomography (CT) scan or standard X-ray, MRI does not use radiation or pose any risk of cancer. • It may be considered first choice in cystic fibrosis and pulmonary embolism of young and pregnant patients. • In other cases (tumors, pneumonia in children), it is an alternative or adjunct to X-ray and CT. In interstitial lung disease, it serves for research, but the clinical value remains to be proven.

MEDIASTINUM1 Mediastinal masses span a wide histopathological and radiological spectrum. The most frequent lesions encountered in the mediastinum are: • Thymoma • Neurogenic tumors • Benign cysts. Mediastinum is further divided into anterior, middle, and posterior compartments. • Anterior mediastinal tumors (account for 50%): –– Thymoma –– Teratoma –– Thyroid disease –– Lymphoma. • Middle mediastinum masses are typically congenital cysts. • Posterior mediastinum masses are often neurogenic tumors. Although CT imaging usually provides the requisite information with mediastinum abnormalities, MRI due to its ability of multiplanar visualization, is used to evaluate the location and extent of disease. MRI is also superior to CT scan in differentiating cystic lesions that appear solid on CT scan.

Neurogenic Tumors (Fig. 60) • Most common cause of a posterior mediastinal mass. • Magnetic resonance imaging is the modality of choice for imaging of neurogenic tumors because it demonstrates its intraspinal extent.

Fig. 60: Magnetic resonance imaging (MRI) scan revealed a 2 cm × 3 cm paravertebral mass in the posterior mediastinum centered at T11–T12 without vertebrae destruction. It came out to be neurogenic tumor after histopathological examination (arrow).

• Neurogenic tumors represent approximately 20% of all adults and 35% of all pediatric mediastinal tumors. • Mediastinal neurogenic tumors are generally grouped into three categories according to tumor origin within the mediastinal nervous tissues namely, (1) the peripheral nerves, (2) sympathetic ganglia, or (3) paraganglia. Each tumor subtype has diverse clinical and radiologic features.

Thymoma • It is the most common primary neoplasm of the anterior mediastinum but accounts for less than 1% of all adult malignancies. • Thymomas typically occur in patients older than 40 years of age, being rare in children, and affecting men and women equally. • At MRI, thymomas commonly appear as homogeneous or heterogeneous masses with low to intermediate signal intensity on T1-weighted images and with high signal intensity on T2-weighted images. MRI can prove useful in identifying the nodular wall thickening detected in cystic thymomas, absent from congenital cysts.

Cystic Masses (Figs. 61A to E) • Mediastinal primary cysts represent 15–20% of all primary mediastinal masses.

  Basic Magnetic Resonance Imaging Pathologies  171

A

C

B

D

E

Figs. 61A to E: Mature cystic teratoma in a 20-year-old female who had chest pain and dyspnea. (A) Contrast-enhanced computed tomography (CT) shows a heterogeneous mediastinal mass with fat-containing areas (arrows). (B) Coronal T1-weighed MR image shows a mass with low signal intensity and areas of fat with high signal intensity (arrows). (C) On T2-weighted magnetic resonance (MR) image, the mass shows a multilocular appearance with high signal intensity (arrows). (D) T2-weighted fat-suppressed MR image shows that the mass contains a high signal intensity of multilocular cystic mass and nodular areas with low signal intensity (arrows). (E) Photograph of the specimen.

• A smooth or oval mass with a homogeneous attenua­ tion, with no enhancement of cyst contents and no infiltration of adjacent structures are the usual CT features of benign mediastinal cyst. • Any cyst may have a higher attenuation due to its calcic, proteinaceous, mucous or hemorrhagic content. Cysts typically show high signal intensity on T2-weighted MR images.

MALIGNANT PLEURAL DISEASES2 (FIG. 62) • Metastatic disease accounts for the vast majority of malignant pleural thickening. Approximately 40% of pleural metastases arise from primary bronchogenic tumors, 20% from breast carcinoma, and 10% from lymphoma. • Magnetic resonance imaging, although not commonly performed, can occasionally be useful in differentiating benign from malignant pleural disease. In particular,

Fig. 62: Pleural mesothelioma on right side.

signal hypointensity relative to the intercostal muscles has been shown to be a reliable predictor of benign disease.

172  Magnetic Resonance Imaging

A

B Figs. 63A and B: Abdominal aortic aneurysm.

Fig. 64: MRI showing the anatomy and function of the heart.

• Malignant mesothelioma is the most common primary pleural neoplasm and almost invariably affects people previously exposed to asbestos. Men are more frequently affected, with a peak incidence between 50 years and 70 years of age. • Magnetic resonance imaging has a limited role in the investigation of pleural disease because of poor spatial resolution and motion artifact.

of the aneurysm, and involvement of major branch vessels. • The risk of rupture increases with increasing aortic diameter, with a high risk of complications (rupture and dissection) at 6 cm for the ascending and 7 cm for the descending thoracic aorta.

AORTA (FIGS. 63A AND B)

MRI is useful in: • Evaluating the anatomy and function of the heart chambers, valves, size and blood flow through major vessels, and surrounding structures such as the peri­cardium. • Diagnosing a variety of cardiovascular (heart and/or blood vessel) disorders such as tumors, infections, and inflammatory conditions. • Evaluating the effects of coronary artery disease such as limited blood flow to the heart muscle and scarring within the heart muscle after a heart attack.

Magnetic resonance angiography (MRA) has gained broad acceptance and is fast becoming a routine in evaluation of the thoracic aorta. Magnetic resonance imaging mainly provides a useful adjunct to CT imaging of the aorta generally outside the acute setting. The lack of ionizing radiation makes it particularly useful for the surveillance of younger patients with aortic pathology. • An ascending aortic diameter equal to or greater than 4 cm and a descending aortic diameter larger than 3 cm is usually considered to indicate dilatation and a diameter exceeding 1.5 times the expected normal diameter is considered an aneurysm. • Infection, inflammation, syphilis, and cystic medial necrosis are other causes for aortic aneurysms, the last being the most common cause of an aneurysm isolated to the ascending aorta. • When imaging an aortic aneurysm, it is important to exactly evaluate the maximal diameter, the length

HEART AND PERICARDIUM3 (FIG. 64)

Constrictive Pericarditis (Figs. 65A and B) • Chronic fibrosing pericarditis is characterized by a thickened, fibrotic and/or calcified pericardium, not infrequently constricting the heart and impairing cardiac filling (“constrictive” pericarditis). • Patients with pericardial constriction typically present with manifestations of elevated systemic venous pressures and low cardiac output. The diagnosis

  Basic Magnetic Resonance Imaging Pathologies  173

A

B

Figs. 65A and B: Classic presentation of constrictive pericarditis on T1-weighted fast spin-echo cardiovascular magnetic resonance (CMR), axial view (A); and short-axis view (*) and (arrows) (B). Extensive pericardial thickening is found on the laterobasal and inferior part of both right and left ventricle and atrioventricular grooves (arrows). The thickened areas are irregularly defined, and are compressing the adjacent cardiac cavities, mainly on the right.

A

B

C

Figs. 66A to C: Moderate pericardial effusion. T1-weighted spin-echo cardiovascular magnetic resonance (CMR). The pericardial effusion (*), having an inhomogeneous spread, is most pronounced over the right atrium and left ventricle. Systolic collapse of the right atrial wall during systole (arrow) (C). The fluid signal intensity, especially on T2, has an inhomogeneous appearance (B). Moderate right-sighted pleural effusion (A).

should always be considered in patients presenting with predominant right heart failure symptoms. • The pathophysiological hallmarks of pericardial constriction, which are caused by confinement of the cardiac chambers by the rigid, fixed pericardial volume, are equalization of end-diastolic pressures in all four cardiac chambers, and increased ventricular coupling which is strongly influenced by respiration.

Pericardial Effusion (Figs. 66A to C) • Abnormal fluid accumulation may be seen in heart failure, renal insufficiency, infection (bacterial, viral,

and tuberculous), neoplasm (carcinoma of lung, breast, and lymphoma), trauma, and myocardial infarction. • Imaging is often required to confirm the presence, severity and extent of fluid; to characterize the nature of fluid; to rule out pericardial inflammation; to determine the hemodynamic impact on the heart; and to guide pericardiocentesis. • For this purpose, echocardiography is the standard. However, image quality and interpretation may be hampered by acoustic window, and in obese patients or in those with obstructive lung disease, necessitating additional imaging, such as CT or MRI.

174  Magnetic Resonance Imaging

REFERENCES 1. Juanpere S, Cañete N, Ortuño P, et al. A diagnostic approach to the mediastinal masses. Insights Imaging. 2013;4(1):29-52.

2. Evans AL, Gleeson FV. Radiology in pleural disease: State of the art. Respirology. 2004;9(3):300-12. 3. Bogaert J, Francone M. Cardiovascular magnetic resonance in pericardial diseases. J Cardiovasc Magn Reson. 2009; 11(1):14.

MULTIPLE CHOICE QUESTIONS



1. Magnetic resonance imaging (MRI) thorax is better than CT scan because: a. Reduced radiation exposure b. Better visualization of lung parenchyma c. Reduced price d. All of the above



6. Most common primary neoplasm of the anterior mediastinum: a. Thymoma b. Neurogenic tumor c. Benign cyst d. Liposarcoma



2. Neurogenic tumors are found in which part of mediastinum? a. Anterior b. Middle c. Posterior d. Apical



7. Mediastinum is divided into __ compartments. a. 5 b. 6 c. 3 d. 2



8. Magnetic resonance imaging (MRI) may be considered modality of choice in: a. Cystic fibrosis in young patient b. Cystic fibrosis in pregnant female c. Both a and b d. None



9. Neurogenic tumors are most commonly found in: a. Anterior mediastinum b. Posterior mediastinum c. Middle mediastinum d. All of the above



3. Cysts typically show which type of attenuation on T2-weighted images? a. High b. Iso c. Low d. None



4. Mesothelioma is a common tumor of: a. Lung b. Pleura c. Pulmonary artery d. Trachea



5. Aortic aneurysm is commonly found at: a. Arch of aorta b. Ascending aorta c. Descending aorta d. All of the above

10. The most common primary pleural neoplasm is: a. Malignant mesothelioma b. Lymphoma c. Both a and b d. None

ANSWERS 1. a 9. b

2. c 10. a.

3. a

4. b

5. c

6. a

7. c

8. c

  Basic Magnetic Resonance Imaging Pathologies  175

SHOULDER JOINT

INTRODUCTION Magnetic Resonance Imaging Standard Views • Axial extending from level of acromion through the glenoid • Oblique coronal • Oblique sagittal.

ROTATOR CUFF TEARS • Supraspinatus is the most common muscle torn. • Occurs from end result of chronic subacromial impinge­ ment and progressive tendon degeneration from traumatic injury. • Inciting injury is often a fall onto an outstretched arm, direct blow to shoulder, or a rapid accelerating incident (pulling on a starter cable). • Patients with a history of recurrent rotator cuff tendinitis are at increased risk for a tear

Normal Coronal Oblique (Fig. 67) The normal coronal oblique view is shown in Figure 67.

Normal Sagittal View (Fig. 68) The normal sagittal view is given in Figure 68.

Magnetic Resonance Imaging Full Thickness Tear • Defects are filled with fluid, granulation tissue or synovium. • Thus defects have fluid like signal on magnetic resonance (MR). • Might also see tendon retraction • Spine of scapula separates supraspinatus from infra­ spinatus on axial images.

Complete Full Thickness Supraspinatus Tear (Fig. 69) The complete full thickness supraspinatus tear is shown in Figure 69.

Complete Full Thickness Supraspinatus Tear (Fig. 70) The complete full thickness supraspinatus tear is shown in Figure 70.

Complete Full Thickness Supraspinatus Tear (Figs. 71A and B) The complete full thickness supraspinatus tear is given in Figure 71.

Partial Thickness Tears1 (Figs. 72A to C)

Fig. 67: Normal coronal oblique.

• Partial thickness tears involve a part of supraspinatus, and are more common along articular surface. • Articular surface partial tear involves the part of muscle in proximity to articular surface and are generally not associated with degenerative changes. • On magnetic resonance image (MRI), partial thickness tear appears as altered signal intensity on T1 and T2 images but more weightage should be given to T2 alteration as T1 alteration may be due to magic angle artifact. • Bursal side partial thickness tear lies on the bursal side of supraspinatus and is usually associated with degenerative changes in coracoacromial ligament and acromion.

176  Magnetic Resonance Imaging

Fig. 68: Normal sagittal view.

Fig. 69: Complete full thickness supraspinatus tear (arrow).

A

Fig. 70: Complete full thickness supraspinatus tear (arrow).

B Figs. 71A and B: Complete full thickness supraspinatus tear (arrows).

  Basic Magnetic Resonance Imaging Pathologies  177

A

B

C

Figs. 72A to C: Partial thickness tears. (A) Articular; (B) bursal; and (C) intrasubstance partial tears of supraspinatus.

Impingement (Fig. 74) • Clinically pain with abduction and external rotation or elevation with internal rotation. • Conditions that limit space within this arch can lead to impingement and eventual tears in supraspinatus tendon.

Types of Acromion Four types of acromion are described by Bigliani: Type I: Flat inferiorly Type II: Curves smoothly Type III: The most anterior portion of the acromion has a hooked shape. Fig. 73: Partial thickness tears of supraspinatus (arrow).

• Intrasubstance tear is present within the supraspinatus muscle.

Partial Thickness Tear of Supraspinatus (Fig. 73) The partial thickness tears of supraspinatus is shown in Figure 73.

Type IV: It has convex inferior contour. • Type III causes most severe form of impingement followed by type II. • Primary impingement is reduced acromiohumeral space. • Secondary impingement is glenohumeral insta­ bility, i.e. excessive overhead use of arm leads to impingement.

178  Magnetic Resonance Imaging

Fig. 74: Types of acromion as described by Bigliani.

REFERENCE 1. Bradley YC, Chandnani VP, Gagliardi JA, et al. Partial thickness supraspinatus tears: diagnosis by magnetic resonance arthrography. Australasian Radiology. 1995;39: ­ 124-7.

MULTIPLE CHOICE QUESTIONS



1. False statement about MRI shoulder is: a. Can differentiate complete and partial tear b. Axial plane is best to demonstrate subscapularis tear c. Tears commonly happen just proximal to musculotendinous junction d. Infraspinatus is most common tendon to be torn 2. Which of them does not cause glenohumoral instability? a. Bankart lesion b. Hill-Sach lesion c. Capsular avulsion d. Labral tear



3. Which type of acromion causes most severe form of impingement? a. Type I b. Type II c. Type III d. Type IV



4. True about shoulder joint is: a. Field of view of 10 cm is required b. T1WI are optimal for joint anatomy

c. Coronal plane is perpendicular to glenoid plane d. Oblique coronal images are acquired parallel to infraspinatus

5. Which muscle is not a part of rotator cuff? a. Supraspinatus b. Pectoralis major c. Pectoralis minor d. Subscapularis



6. How many types of acromion are described by Bigliani? a. 5 b. 6 c. 4 d. 3



7. Intrasubstance tear is present: a. Within the supraspinatus muscle b. Outside the supraspinatus muscle c. Can be both d. None



8. Which muscle of rotator cuff is most prone to tear? a. Supraspinatus b. Infraspinatus c. Teres minor d. Subscapularis

  Basic Magnetic Resonance Imaging Pathologies  179

9. Type I acromion as described by Bigliani is: a. Flat anteriorly b. Flat inferiorly c. Flat posteriorly d. Flat superiorly

10. Clinical signs of impingement are: a. Pain in abduction b. Elevation with internal rotation c. Both a and b d. None

ANSWERS 1. d 9. b

2. b 10. c.

3. c

4. c

5. b

6. c

7. a

8. a

KNEE JOINT

INDICATIONS OF KNEE JOINT MAGNETIC RESONANCE IMAGING • Knee pain, weakness, swelling or bleeding in the tissues in and around the joint • Damaged cartilage, meniscus, ligaments or tendons • Sports-related knee injuries, such as sprains, torn ligaments and torn tendons • Bone fractures that may not be visible on X-rays and other imaging tests • Degenerative joint disorders, such as arthritis • Build-up of fluid in the knee joint • Infections of bones • Primary tumors and metastasis involving bones and joints.

Morphologic Changes Associated with Meniscal Tear • • • • •

Blunting of tip of inner free edge of meniscus Displacement of a portion of meniscus Interrupted appearance of meniscus Abnormal size of a segment of meniscus When a portion of free margin of meniscus is detached it is called bucket handle tear.

Note: When posterior horn is equal or smaller than anterior horn, despite a normal triangular contour a tear must be suspected as posterior horn of medial meniscus is normally almost twice the size of anterior horn.

CRUCIATE LIGAMENTS INJURY1

MENISCAL TEARS

Anterior Cruciate Ligament (Fig. 76)

Stoller and Colleagues Grading (Figs. 75A to D)

Anterior cruciate ligament (ACL) provides most significant stabilizing mechanism against anterior translation of tibia. ACL is 1 cm wide and 3–4 cm long. ACL has straight taut fibers that run parallel to roof of intercondylar notch.

• Grade I: Globular signal intensity within the meniscus not contiguous with the articular surface. • Grade II: Linear signal intensity not contiguous with articular surface. • Grade III: Regions of signal intensity extending up to articular surface. When abnormal signal contacting the surface is seen only in one image the diagnosis of possible tear rather than definitive tear should be made.

Diagnostic Criteria Anterior cruciate ligament tear is diagnosed by alterations in signal intensity, morphology, and course of ligament. A complete ACL tear on coronal images is diagnosed by empty notch sign.

180  Magnetic Resonance Imaging

B

A

D

C

Figs. 75A to D: High signals are noted (arrows) in posterior horn of medial meniscus.

Fig. 76:

Contd...

  Basic Magnetic Resonance Imaging Pathologies  181 Contd...

Fig. 76: T2 hyperintensity is noted in anterior cruciate ligament (arrows).

A

B

Figs. 77A and B: (A) Normal posterior cruciate ligament (arrow) and (B) torn posterior cruciate ligament (arrow).

Indirect Signs of Anterior Cruciate Ligament Tear • Buckling of posterior cruciate ligament (PCL) giving rise to question mark configuration • Undulation and redundancy of patellar tendon • Uncovered lateral meniscus sign. Anterior tibial subluxation greater than 5 mm with respect to femur is very sensitive and specific sign of complete ACL tear. • Deep lateral femoral notch/sulcus sign (>2 mm). • Avulsion fracture of lateral tibial rim.

• Joint effusion and hemarthrosis is a common finding associated with ACL injuries. • A tibial spine avulsion is uncommon but specific finding for ACL injury.

Posterior Cruciate Ligament (Figs. 77A and B) The PCL is attached to lateral surface of medial femoral condyle crosses ACL and attaches to posterior intercondylar fossa of tibia. It is 3.8 cm in length and 1.3 cm in width at its midportion. PCL prevents posterior translation of tibia. On magnetic resonance imaging (MRI) PCL appears as band-like structure of low signal intensity.

182  Magnetic Resonance Imaging On sagittal images it has an arcuate shape with knee in neutral position.

Osteoarthritis (Fig. 78) Osteoarthritis affects knee more than any other joint. MRI findings of degenerative arthrosis/osteoarthritis are: • Bone marrow edema-like lesions • Subchondral cyst-like lesions • Joint effusion • Synovitis • Subchondral bone attrition • Loose bodies.

REFERENCE Fig. 78: T1-image shows hypointense subchondral cysts-like lesions (thin arrows) and subchondral bone attrition (thick arrow).

1. Girgis FG, Marshall JL, Monajem A. The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis. Clin Orthop Relat Res. 1975;106:216-31.

MULTIPLE CHOICE QUESTIONS



1. Type 1 meniscal injury is: a. Linear signal intensity not contiguous with articular surface b. Globular signal intensity within the meniscus c. Regions of signal intensity extending up to articular surface d. None



2. Most common meniscus involved in injury is: a. Medial b. Lateral c. Anterior d. Posterior



3. Empty notch sign is seen in: a. Lateral collateral ligament tear b. Medial collateral ligament tear c. Anterior cruciate ligament tear d. Posterior cruciate ligament tear



4. Loose bodies are seen in: a. Meniscal tear b. ACL tear c. Osteoarthritis d. PCL tear



5. Which ligament has an arcuate shape with knee in neutral position in sagittal images? a. ACL b. PCL c. Medial collateral ligament d. Lateral collateral ligament



6. Stoller and colleagues grading is used to grade: a. Head injury b. Bone fracture c. Meniscal tear d. None



7. Morphologic changes associated with meniscal tear are: a. Blunting of tip of inner free edge of meniscus b. Displacement of a portion of meniscus c. Interrupted appearance of meniscus d. All of the above



8. MRI findings of osteoarthritis are: a. Loose bodies b. Joint effusion c. Synovitis d. All of the above



9. Anterior cruciate ligament is: a. 1 cm wide and 3–4 cm long b. 3 cm wide and 1–2 cm long c. 3 mm wide and 4–5 mm long d. 5 mm wide and 6–7 mm long

10. Posterior cruciate ligament is: a. 3.8 cm in length and 1.3 cm in width b. 5 mm in length and 7 mm in width c. 9 cm in length and 6 cm in width d. None

  Basic Magnetic Resonance Imaging Pathologies  183

ANSWERS 1. b 9. a

2. a 10. a

3. c

4. c

5. b

6. c

7. d

8. d

WRIST JOINT

CARPAL TUNNEL SYNDROME1

Magnetic Resonance Imaging Features It is most common nerve compression disorder in the (Figs. 79 and 80) upper extremity.

Clinical Features • Chronic discomfort and tingling in the fingers in the median nerve distribution involving thumb and radial half of index finger. • Most patients are between 30 years and 60 years of age with female preponderance. • Tapping median nerve may elicit tingling in the median nerve distribution called as Tinel sign.

A

• • • •

Increased signal intensity of median nerve on T2 Bowing of flexor retinaculum Deep palmar bursitis Swelling is best evaluated at the level of pisiform.

REFERENCE 1. Andreisek G, Crook D, Burg D, et al. Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features. Radiographics. 2006;26(5):1267-87.

B Figs. 79A and B: (A) Normal median nerve (arrow) and (B) flattened median nerve (arrow).

184  Magnetic Resonance Imaging

A

B

Figs. 80A to C: (A and B) Increased signal intensity of median nerve on T2 and (C) carpal tunnel from flexor tendon tenosynovitis (arrows).

C

MULTIPLE CHOICE QUESTIONS



1. Carpal tunnel syndrome involves: a. Radial nerve b. Median nerve c. Ulnar nerve d. All



2. Tinel sign elicited when: a. Flexion of wrist joint b. Flexion of elbow c. Tapping over median nerve d. None



3. Magnetic resonance imaging features of carpal tunnel syndrome is: a. Hyperintense median nerve on T1 b. Superficial palmar bursitis

c. Tenderness over elbow d. Bowing of flexor retinaculum

4. Medial one-half fingers are supplied by: a. Median nerve b. Ulnar nerve c. Radial nerve d. Musculocutaneous nerve



5. Carpal bones are all except: a. Triquetral b. Cuneiform c. Hamate d. Trapezoid

  Basic Magnetic Resonance Imaging Pathologies  185

ANSWERS 1. b

2. c

3. d

4. b

5. b.

DEGENERATIVE DISEASES OF SPINE

INTRODUCTION • Normal aging is a complex physiologic process that encompasses various degrees of gross anatomic and biomedical changes in the entire disco-vertebral complex. • Desiccation, degeneration are part of normal aging, begins in teens, i.e. in 20th decade of life. • Annular tear: Tears of annulus fibrosus occurs with aging. • High signal intensity on T2-weighted imaging (T2WI). • Disk degeneration: Commonly defined as diminished signal on T2WI, combined with loss of disk space height.

• Lumbar and cervical spinal segment commonly affected. • Schmorl’s nodes, herniation of disk material are common. Imaging findings: Schmorl’s nodes, osteophytes and end plate sclerosis, thinned disk space. Coronal T1WI shows thinned disk space, lateral osteo­ phytes and degenerative marrow space.

Spondylosis and Spondylolisthesis (Fig. 82)

SPONDYLOSIS (FIG. 81)

• Spondylosis is a fibrous cleft within pars interarticularis. • Spondylolisthesis is the slippage of one vertebral body in relation to other. • Etiology: Congenital/acquired –– Acquired: Ligamentous laxity trauma. –– It can occur at any age.

• Men > Women. • Primary pathologic features—osteophytes.

Location: Spondylolysis at L5 and L4 commonly, spondylolisthesis at L4-L5-L5-S1.

Fig. 81: Magnetic resonance imaging (MRI) spine showing severe degenerative change between C3/4 and C6/7 with compression of the cord (cervical spondylosis with myelopathy).

Fig. 82: Defect in pars interarticularis on sagittal section of T1weighted image (T1WI).

186  Magnetic Resonance Imaging

Fig. 83: Disk bulge on sagittal section (T2-weighted image).

Fig. 84: Herniated nucleus pulposus (HNP)—herniation of L5-S1 disk (T2-weighted sequence).

Imaging: Defects in pars interarticularis spondylolisthesis anteroposterior (AP) canal diameter is increased and shows double canal appearance.

Flexion injury: Common in cervical and thoracic spine at thoracolumbar junction. • Imaging: Anterior wedging and vertebral body fracture with AP subluxation common.

DISK BULGE (FIG. 83) Due to loss of turgor in nucleus pulposus and decreased elasticity of annulus, the disk bulges outward beyond the vertebral margins. Imaging: Loss of intervertebral disk height, interdiskal gas and end plate osteophytes.

DISK HERNIATION (FIG. 84) • Herniation of nucleus pulposus (HNP) through an annular defect causes focal protrusion of disk material beyond margins of end plate. • Commonly by age of 60 years. • 90% occur at L4-L5 or L5-S1.

Imaging Herniation of nucleus pulposus.

TRAUMA Mechanisms • Flexion • Extension • Axial loading (compression) • Rotational.

Extension injury: Common in cervical region. • Imaging: Posterior element fracture is common, sub­luxation might occur. Axial loading: Compressive and vertical force of others. • Imaging: Lateral mass fracture and facet subluxation common.

Common Injury Patterns Cervical Spine • C1 (Atlas): –– Atlanto-occipital dislocation is often but not invariably fatal. –– Bilateral vertical fracture—(Jefferson fracture that involves both anterior and posterior areas). • C2: Odontoid fracture usually occurs at base of dens (Hangman’s fracture—caused by hyperextension resulting in bilateral neural arch fracture). • C3–C7: Typical flexion injuries including simple wedge fracture of one or more anterior vertebral bodies.

Thoracic Spine Thoracic spine: Less common than cortical and thoracic lumbar junction injury. Thoracic “burst” fracture can occur with severe axial loading.

  Basic Magnetic Resonance Imaging Pathologies  187

Fig. 85: Spinal meningioma on T2-weighted image (sagittal section).

Fig. 86: Thoracic spine schwannoma on T2-weighted imaging (sagittal).

Thoracolumbar junction: Majority of thoracolumbar frac­ ture between T12 and L2. Nearly 75% are compression fracture with anterior wedging.

• Types: Schwannoma, neurofibroma, ganglio neuroma, neurofibrosarcoma (rare) –– MC age: Middle-aged adults.

Soft Tissue Injury • Helpful when neurologic deficits are disproportionate to observed injury. • Magnetic resonance (MR) depicts cord contusion, edema and defects extra-axial lesions, such as epidural hematoma. • Long-term sequelae—cord transaction, traumatic syrinx, etc.

TUMORS1 (FIG. 85)

Various locations: Mostly intradural extramedullary (almost 75%) Clinical symptoms can mimic disk herniation.

Imaging • • • •

Enlarged neural foramina. Calcifications are rare 75% isointenses and 25% hypointense on T1WI More than 95% hypointense on T2WI (target appea­ rance common) • Virtually 100% enhance.

Meningioma

METASTATIC DISEASE (FIG. 87)

• • • • •

Neoplastic Extradural Mass (Most Common)

Most are typical benign meningiomas Second most common cause of spinal tumor Classic patient is middle-aged women Most common location thoracic spine 90% are intradural extramedullary.

Imaging • • • •

Bone erosion, calcifications are rare Most are isointense with cord on T1 and T2WI Moderate contrast enhancement ± dural tail.

Nerve Sheath Tumors (Fig. 86) • Most common intradural extramedullary mass

• Approximately half of all spine metastasis with epidural spinal cord compression arise from breast, lung or prostate. • Middle age and elderly adults are most commonly affected. • Location: Outside of duramater. • Adults: Initial—vertebral body, typically posterior aspect. • Clinical features: Pain and progressive neurologic deficits. • Cord compression. • If untreated—metastatic epidural compression progresses.

188  Magnetic Resonance Imaging

Fig. 87: T2-weighted image (T2WI) shows metastasis from prostate cancer.

Imaging • Mostly osteolytic but can be osteoblastic too. • Pedicle destruction common. Four MR patterns of vertebral metastatic disease: 1.  Focal lytic 2.  Focal sclerotic 3.  Diffuse inhomogenous 4.  Diffuse homogenous • Multifocal lytic lesions are most common—show low signal intensity on T1 and high signal intensity on T2WI. • Sclerotic lesions are hypointense on both T1 and T2WI.

Spinal Cord Astrocytoma Spinal cord astrocytoma has usually two grades: 1. Fibrillary astrocytoma 2. Anaplastic astrocytoma. –– Glioblastoma multiforme (GBM) rare –– Most common spinal cord tumor in children. –– Cause of low back pain and scoliosis in children.

Imaging • Low multisegment intramedullary mass typical, causes diffuse cord expansion.

Fig. 88: Spinal ependymoma.

• Interpedicular distance widened with pedicles thinned. • Usually iso- to hypointense on T1, hyperintense on T2WI. • Cysts common • Virtually 100% enhance.

Spinal Ependymoma (Fig. 88) • Most common spinal cord tumor. • Usually in middle-aged patients. • Conus ependymomas are slow growing, may become extremely large and erode bone.

Imaging • Vertebral body scalloping common with large conus lesion, may enlarge neural foramina. • Hemorrhage is common and cysts are frequent. • Usually isointense with cord on T1, hyperintense on T2WI. • Enhances strongly.

REFERENCE 1. Kim Daniel H, Chang Ung-Kyu, Kim Se-Hoon, et al. Tumors of the Spine. First Edition. Philadelphia: Saunders-Elsevier; 2008. pp. 185, 190.

  Basic Magnetic Resonance Imaging Pathologies  189

MULTIPLE CHOICE QUESTIONS



1. Primary finding in spondylosis: a. Osteophytes b. Spinal cysts c. Annular tear d. Bulge



2. Most common extradural malignant neoplasm of spine: a. Lymphoma b. Chordoma c. Ewing’s sarcoma d. Metastasis





3. Jefferson fracture is fracture of: a. C1 b. C2 c. C3 d. C4

9. Mostly meningiomas are ________ in location. a. Intradural extramedullary b. Extramedullary intradural c. Can be both d. None

10. Nearly half of the metastasis of spine in females is from: a. Breast b. Cervix c. Ovaries d. Liver



4. Vacuum disk phenomenon is a sign of: a. Trauma b. Degeneration c. Infection d. Malignancy

11. Nearly half of the metastasis of spine in males is from: a. Prostate b. Liver c. Spleen d. Kidneys



5. Polka-dot sign is seen in: a. Hemangioma b. Metastasis c. Chordoma d. Astrocytoma

12. Most common spinal cord tumor is: a. Meningioma b. Astrocytoma c. Ependymoma d. Nerve sheath tumor



6. Schmorl’s nodes are seen in: a. Spondylosis b. Disk bulge c. Spondylolisthesis d. None

13. Most common spinal cord tumor in children is: a. Astrocytoma b. Ependymoma c. Meningioma d. Nerve sheath tumor



7. Mechanism in trauma to spine involves: a. Flexion b. Extension c. Axial loading d. All of the above

14. Which vertebrae are commonly known as Atlas? a. C1 b. C2 c. T4 d. S1



8. Hangman’s fracture is fracture of: a. C1 b. C2 c. C3 d. C4

15. Which vertebrae is commonly known as Axis? a. C1 b. C2 c. T4 d. S1

ANSWERS 1. a 9. a

2. d 10. a

3. a 11. a

4. b 12. c

5. a 13. a

6. a 14. a

7. d 15. b

8. b

190  Magnetic Resonance Imaging

INFECTION OF BONES

TUBERCULOSIS1 • Osteoarticular tuberculosis is second most common to spine. • It begins in synovium or the metaphysis. • Synovial infection occurs via contiguous spread or via hematogenous spread. • As compared to pyogenic infections, sequestration, and periosteitis are not very common.

It is seen in 15% cases of osteoarticular tuberculosis. Tuberculosis infection may occur in greater trochanter and manifest as surface erosion or lytic lesion in greater trochanter.

Clinical Features

Tuberculosis Hip Joint (Figs. 89 and 90)

• Low-grade fever, anorexia, weight loss, and night sweats. • Night pains, painful limitations of movements, and regional lymph nodes involvement.

The main causative organism is Mycobacterium tuber­culo­ sis, however atypical mycobacteria, i.e. Myco­bacterium kansasii, Mycobacterium xenopi and Myco­bacterium aviumintracellulare are also isolated in immunocompromised individuals. The organism reaches the bone and remains dormant until recrudescence occurs. Any factor which modifies the state of local resistance and resultant activation of dormant tubercle bacilli. Sites involved are acetabulum, synovium, femoral epiphysis and metaphysis.

The disease is classified into three stages: 1. Stage of synovitis: Joint effusion and synovial hyper­ trophy causes soft tissue swelling and joints widening. 2. Stage of arthritis: Deformity of hip joint is present. Localized erosions can be seen in periarticular region that causes reduction in joint space. 3. Stage of advanced arthritis: As the disease progresses, there is destruction of articular cartilage, acetabulum, femoral head, capsule, and ligaments. As femoral head is displaced upward, there is break in Shenton’s line and wandering acetabulum is seen.

Fig. 89: Gadolinium-enhanced transverse T1-weighted magnetic resonance (MR) images show abscesses (arrows) associated with hip joint infection in the right thigh and have thin, smooth, and enhancing rims.

Fig. 90: Gadolinium-enhanced coronal T1-weighted magnetic reso­ nance (MR) images of the hip show irregular borders (arrows) and extra-articular spread of pyogenic arthritis, with a feathery appearance, into adjacent muscles.

  Basic Magnetic Resonance Imaging Pathologies  191

Fig. 91: Sagittal T1-weighted magnetic resonance (MR images show bone erosions of well-defined hypointense lesions (short arrows) and hypointense marrow (long arrows) in both the femur and tibia.

Fig. 92: Sagittal T1-weighted magnetic resonance (MR) images show tuberculous arthritis involving knee shows bone erosions of well-defined hypointense lesions (short arrows) and hypointense marrow (long arrows) in both the femur and tibia.

• T2: Hyperintense • Contrast study shows: Brilliant enhancement MRI can assess associated abnormalities (e.g. osteo­ myelitis, myositis, cellulitis, para-articular abscess, teno­ synovitis, bursitis, skin ulceration or sinus tract formation): • Sinus tracts appear linear T2 hyperintensity with marginal “tram-track enhancement” • Para-articular abscesses have thin, smooth, and enhancing wall.

Tuberculosis Knee (Figs. 91 to 93) It occurs at any age. The knee joint has the largest intra-articular space and is involved in 10% cases of osteoarticular tuberculosis. Fig. 93: Sagittal T2-weighted magnetic resonance (MR) images of the knee show the signal intensity of synovial abnormalities and increased bone marrow signal intensity (arrows) with predominantly intermediate signal intensity (white arrowheads) with small amounts of hyperintense joint fluid (black arrowheads).

Further advanced stages show collapsed femoral head and neck with enlarged acetabulum, so called “mortar and pestle” appearance.

Magnetic Resonance Imaging The lesions are typically: • T1: Hypointense

Clinical Features Pain on movement, synovial effusion, and palpable synovial thickening. • Stage of synovitis: Osteoporosis, thickened synovium, and capsule, synovial effusion. Widening of intra­ condylar notch. Purulent material can accumulate in the joints with destruction of articular cartilage. • Stage of arthritis: Erosion of articular surface, decrease joint spaces with bony destructions. • Stage of advanced arthritis: Osteolytic cavities are seen with or without sequestra formation, marked reduction in joint spaces, destruction and deformity of joints.

192  Magnetic Resonance Imaging

B

A Fig. 94: Magnetic resonance imaging (MRI) of lower end of femur suggestive of acute osteomyelitis with large collection of abscess in deep posterolateral aspect of thigh along with infiltration of adjacent muscles.

Figs. 95A and B: Magnetic resonance (MR) images of same patient. (A) T1-weighted image showing decreased bone marrow signal (arrows), due to edema consistent with osteomyelitis; and (B) T2weighted image of the same patient showing increased signal from bone marrow (arrow), cutaneous ulcer (arrowhead), and a soft tissue collection (dashed arrow).

C

A

B

D

Figs. 96A to D: The area of abnormality has slight low to intermediate signal intensity on T1-weighted image (T1WI) and very high signal intensity on T2WI. The lesion does not cross the epiphyseal plate distally, of the left femur, and the epiphysis demonstrates normal signal intensity. A slight periosteal reaction can be seen on the T2WI. However, no mass or edema is seen in the surrounding soft tissue. On the contrastenhanced MRI, patchy enhancement is seen within the area of involved bone marrow. Tissue pathology revealed chronic osteomyelitis.

PYOGENIC INFECTIONS2 In infants, Streptococcus is common infecting organism and in adults, Staphylococcus is most common organism. Bony spread occurs via hematogenous routes.

• Edema and inflammatory changes show high signal intensity on T2-weighted images and on STIR sequences. • Abscesses, if present, appear as well-circumscribed area of decreased signal intensity on T1 images with rim enhancement on contrast T1 images.

On Magnetic Resonance Imaging

Chronic Osteomyelitis (Figs. 96A to D)

• Low signal intensity on T1-weighted images and high signal on T2-weighted images/STIR with postcontrast enhancement.

It usually results from inadequately treated acute osteo­ myelitis or from infections following compound bone fracture.

Acute Osteomyelitis (Figs. 94 and 95)

  Basic Magnetic Resonance Imaging Pathologies  193

A

B

C

Figs. 97A to C: Magnetic resonance Imaging (MRI) of a patient; (A) T1-weighted sequence reveals the penumbra sign; (B) T2-weighted turbo spin echo sequence (TSE) reveals the penumbra sign; and (C) magnetic resonance (MR) image STIR-TSE sequence shows the penumbra sign.

A well-circumscribed area of bone destruction has a surrounding zone of reactive sclerosis with or without periosteal reaction.

On Magnetic Resonance Imaging

A

B

Figs. 98A and B: Contrast-enhanced fat suppressed T1-weighted (T1W) images of left knee. (A) magnetic resonance imaging (MRI) shows synovial enhancement, joint effusion, diffuse soft tissue edema (arrows); (B) synovial enhancement, effusion and edema showed significant improvement after treatment (arrows).

On Magnetic Resonance Imaging • Active foci of infections shows low to intermediate signal intensity on T1- and high signals on T2-weighted images. • Involucrum manifests as a well-defined rim of low signal intensity on all sequences. • Surrounding granulation tissue appears as hypointense on T1-images, hyperintense on T2/STIR and shows contrast enhancement. • Sinus tract shows linear or curvilinear area of low signal on T1 and high signals on T2/STIR extending in contiguity from medullary cavity with cortical disruption.

Brodie’s Abscess (Figs. 97A to C) It is a localized form of osteomyelitis and usually found in cancellous tissue near the long bones.

T2 hyperintense nidus, sclerotic rim and bone edema with center of lesion show low signals due to necrotic material. T1-weighted images show “penumbra sign” as a discrete peripherally zone of marginally higher signal intensity surrounding marrow edema.

Septic Arthritis (Figs. 98A and B) • It usually follows hematogenous route but other causes are post-trauma, joint aspiration, soft tissue infection or periarticular osteomyelitis. • Staphylococcus aureus is most common affecting organism. • Fever, chills, severely tender swollen joints are common presentations. • Knee joint is most frequently affected. • MRI helps to differentiates it from transient synovitis that usually occurs in pediatric population. • Postcontrast T1W images shows thickened enhancing synovium with intraosseous abscesses with bone destruction with marrow enhancement. • No marrow changes are seen in transient synovitis.

REFERENCES 1. Sharma P. MR features of tuberculous osteomyelitis. Skeletal Radiol. 2003;32(5):279-85. 2. Tang JS, Gold RH, Bassett LW, et al. Musculoskeletal infection of the extremities: evaluation with MR imaging. Radiology. 1988;166(1 Pt 1):205-09.

194  Magnetic Resonance Imaging

MULTIPLE CHOICE QUESTIONS



1. Stage of advanced arthritis in TB hip presents with: a. Joint effusion b. Bony destruction c. Wandering acetabulum d. All of above



2. Widening of intracondylar notch appears in which stage of TB knee joint? a. Stage 1 b. Stage 2 c. Stage 3 d. Stage 4



3. Most common mode of infection spread in pyogenic osteomyelitis is: a. Lymphatics b. Hematogenous c. Direct spread d. All of the above



4. “Penumbra sign” is seen in: a. Acute osteomyelitis b. Chronic osteomyelitis c. Tubercular osteomyelitis d. Brodies abscess.





c. Stage of advanced arthritis d. None

7. “Tram-track enhancement” is seen in: a. Sinus tract formation b. Cellulitis c. Myositis d. None



8. Causative organism of osteomyelitis in adults is: a. Streptococcus b. Staphylococcus c. Klebsiella d. Mycobacterium



9. Causative organism of osteomyelitis in infants is: a. Streptococcus b. Staphylococcus c. Klebsiella d. Mycobacterium

10. “Penumbra sign” is seen in: a. Osteomyelitis b. Brodie’s abscess c. TB knee joint d. None 11. “Penumbra sign” is seen on: a. T1WI b. T2WI c. FLAIR d. All of the above

5. Septic arthritis does not show: a. Mortar and pestle appearance b. Thickened enhancing synovium c. Intraosseous abscesses d. Marrow enhancement 6. “Mortar and pestle” appearance is seen in: a. Stage of synovitis b. Stage of arthritis

12. Most common organism causing septic arthritis is: a. Staphylococcus aureus b. Bacillus cereus c. Streptococcus pneumonia d. Klebsiella pneumonia

ANSWERS 1. d 9. a

2. a 10. b

3. b 11. a

4. d 12. a

5. a

6. c

7. a

8. b

  Basic Magnetic Resonance Imaging Pathologies  195

INFECTIONS OF SPINE

TUBERCULOSIS1 The spine is the most common site of bone tuberculosis. Tubercular spondylitis is defined as an infection by Mycobacterium tuberculosis in one or more of the extradural components of spine namely the vertebra, intervertebral disk spaces, paraspinal soft tissue and epidural space (Figs. 99 to 102).

Pathophysiology Spread of infections occurs from hematogenous routes from a primary focus in lung, gastrointestinal tract (GIT) or any other viscera which may be active. Usually lower thoracic and lumbar vertebrae are most commonly affected. The infection begins in the paradiskal area of vertebrae. Anterior wedging is commonly seen in dorsal spine. When infection spread to adjacent disk spaces, it narrows the disk spaces. The intervertebral disk usually resists the tubercular infection due to lack of proteolytic enzymes in Mycobacterium as compared to pyogenic infections. Involvement of posterior elements is also more common in tubercular than in pyogenic infections. As disk is avascular, it resists as an initial site of infection. Thick pus formation occurs in tubercular infections due to hypersensitivity reactions to Mycobacterium. The pus tracks through the surrounding soft tissues and leads

A

B

to formation of pre- and paravertebral abscesses. This further spreads and causes epidural abscess and cord compression.

Clinical Features Usually patients presented are of third decades and complain of persistent spinal pain, local tenderness and limitations of spine mobility. The erythrocyte sedimentation rate (ESR) is elevated and tuberculin test is positive. Paraparesis occurs in 20–30% cases and if cervical spine is involved, leads to quadriparesis.

Magnetic Resonance Imaging • It is the imaging modality of choice in detecting and staging the inflammatory and infective etiology of spine. • It can detect early bone marrow involvement or edema of spinal cord and neural involvement. Soft tissue abscesses are also detected on magnetic resonance image (MRI). • Although calcifications are not readily detected on MRI. T1-weighted (T1W) images usually show decreased signals within the affected vertebral marrow and loss of

C

Figs. 99A to C: Tuberculosis of the spine. T2-weighted (T2W) (A); T1W (B) axial MRI images in a 12-year-old girl with upper dorsal spine tuberculosis show a small prevertebral abscess (arrow). Wedging of the D2 vertebral body is seen with marrow involvement. Sagittal ADC map; and (C) sagittal images show increased diffusion (arrow) in the involved vertebra.

196  Magnetic Resonance Imaging

B

A

C

D

E

Figs. 100A to E: Tuberculosis of the spine. Sagittal T1-weighted (T1W) (A) and T2W (B) images in an elderly patient with tuberculosis show multifocal dorsal vertebral body involvement (arrows) with an epidural soft tissue component. Sagittal ADC map (C) and axial T2W (D) and diffusion (E) images show increased diffusion (arrows) in the involved vertebrae.

A

B

C

Figs. 101A to C: Tuberculosis of spine. Sagittal T1W (A) and T2W (B) images in a 40-year-old patient with spinal tuberculosis show a well-defined rounded lesion (arrows) with T1 hypointensity and T2 isohypointensity, which was difficult to characterize on routine magnetic resonance imaging (MRI). Sagittal ADC map (C) reveals increased diffusion in the lesion.

A

B

Figs. 102A and B: Tuberculosis of the spine. Sagittal T1-weighted (T1W) image of a 35-year-old patient shows multiple vertebral body lesions (arrows) and wedging of L1, with no significant soft tissue component. It is not possible to differentiate between tuberculosis and metastases. Sagittal ADC map (B) reveals increased diffusion in the lesions.

  Basic Magnetic Resonance Imaging Pathologies  197

Fig. 103: Magnetic resonance image (MRI) of the lumbar spine showing an infection that started in the disk (discitis) and has spread into the vertebral bones above and below (osteomyelitis) (arrows).

Fig. 105: Discitis/osteomyelitis is seen on this T2-weighted magnetic resonance image (MRI) of the lumbar spine, which demonstrates destruction of the L3-4 disk space with the adjacent endplate and/or vertebral body. L3 and L4 vertebral bodies show increased T2 signal, indicating edema and/or infarction. Also shown is a retropulsion of debris, which compresses the thecal sac.

cortical definition of affected vertebrae. T2W images show increased in signal intensity in involved vertebral bodies and disks. • Paraspinal soft tissue masses are seen in majority of cases. T1W images show loss of uniform psoas muscle signal intensity and enlargement of affected muscles. T2W images show increase in signal intensity in affected paraspinal muscles.

Fig. 104: Magnetic resonance image (MRI) demonstrates partial volume loss of the upper aspect of the T6 vertebral body on the right (yellow arrows) in our patient with chronic recurrent multifocal osteomyelitis, the third rib (white arrow) is enlarged and has scattered areas of increased signal intensity.

• Postcontrast images show thick rim enhancement around the intraosseous and paraspinal soft tissue abscesses. • The soft tissue masses displace the thecal sac and spinal canal is distorted. Postcontrast fat suppressed images demonstrate the meningeal and epidural inflammatory soft tissue with improved definition of cord and compromise of nerve roots. • Cord changes can be interpreted as edema of cord, myelomalacia, atrophy of cord or syringomyelia. • Edema is seen as hyperintense signal on T2W images but no signal alteration on T1. • Myelomalacia shows hypointense signal on T1 and may be associated with thinning of the cord. • Syrinx is a tubular, well-defined fluid-filled region within the spinal cord.

PYOGENIC INFECTIONS2 (FIGS. 103 TO 107) Staphylococcus aureus is most commonly affecting organism, followed by Streptococcus, pneumococcus and gram-negative organisms. Higher incidence is seen in the debilitated, diabetic, and in elderly. The pathogen can reach the spine via many routes. • Arterial hematogenous • Venous hematogenous • Contiguous spread • Direct inoculation.

198  Magnetic Resonance Imaging

A

B

C

D

Figs. 106A to D: Bacterial discitis/osteomyelitis. (A) Sagittal precontrast T1 image shows low signal intensity from the T-12 and L-1 vertebral bodies with narrowing of the intervening disk space and erosions of the end-plates; (B) Corresponding T2 image shows similar findings and subtle increased T2 signal in the affected vertebral bodies; (C) Corresponding T1 image after contrast administration shows enhancement of the affected vertebrae, disk, and paraspinal soft tissues; and (D) Axial postcontrast T1 image at the involved level shows a right paraspinal mass comparable with a phlegmon.

A

B

C

Figs. 107A to C: Magnetic resonance image (MRI) of thoracic spine, sagittal spin echo T1 sequences, with (A) and without contrast (B), and STIR (fat suppression) (C) sequence, where extensive epidural and paravertebral soft tissue involvement is observed reducing the diameter of the spinal canal, with a small D7-D8 prevertebral abscess.

Vertebral bodies and intervertebral disk are most frequently affected with primary or secondary involvement of epidural space, posterior elements and paraspinal soft tissue. Osteomyelitis occurs most commonly at end plates because of presence of large number of arteries at this location. The early infectious lesion occurs in the anterosuperior subchondral region of the vertebral body and subsequently extends through the end plates. The infection involving the vertebral end plates easily extends

to the adjacent disk space because the intervertebral disk receives the nutrition from blood vessels located in cartilaginous end plates in children, but it is not so in adult spine, where the nutrition occurs primarily by process of diffusion.

Clinical Features • Usually there is history of recent primary infection of skin, urinary tract or respiratory tract.

  Basic Magnetic Resonance Imaging Pathologies  199 • Back pain that gets aggravated by movements. • Fever, malaise. Local tenderness. • Spread of infection to epidural spaces leads to neuro­ logical symptoms.

Magnetic Resonance Imaging • The vertebra usually shows low signal intensity on T1W and high signal on T2W and these signals represent edema and destructive changes. • The intervertebral disk usually shows high signal on T2W with decrease in vertebral height. • Loss of margins between disk and vertebral bodies on T2W images.

• Diffuse and homogenous enhancement seen in affec­ ted marrow and disk. • The vertebra; end plates are indistinct and shows low signal intensity onT1W images and high signal on T2W or proton density images.

REFERENCES 1. Francis IM, Das DK, Luthra UK, et al. Value of radiologically guided fine needle aspiration cytology (FNAC) in the diagnosis of spinal tuberculosis: a study of 29 cases. Cyto­ pathology. 1999;10:390-401. 2. Friedman JA, Maher CO, Quast LM. Spontaneous disc space infections in adults. Surg Neurol. 2002;57(2):81-6.

MULTIPLE CHOICE QUESTIONS

1. A middle-aged female with complain of chronic backache. MRI shows collapse of D12 vertebrae but intervertebral disk spaces are maintained. All are possible except: a. Multiple myeloma b. Osteoporosis c. Metastasis d. Tuberculosis

c. Posterior element involvement d. Contiguous involvement of two or more vertebrae

6. Most common site of bone tuberculosis is: a. Spine b. Long bones c. Flat bones d. All of the above



2. Tuberculosis of spine first starts in: a. Vertebral body b. Nucleus pulposus c. Annulus fibrosis d. Paravertebral joints



7. In pyogenic infections the route of inoculation is: a. Hematogenous b. Contiguous spread c. Direct inoculation d. All of the above



3. Intervertebral disks usually show resistance to: a. Fungal infections b. Tubercular infections c. Pyogenic infections d. All of the above



8. Causative organism for TB spine is: a. Mycobacterium b. Staphylococcus c. Streptococcus d. Klebsiella



9. The imaging modality of choice in detecting and staging the inflammatory and infective etiology of spine is: a. CT b. MRI c. PET d. X-ray



4. Postinfective vertebral collapse is seen in: a. Cervical vertebrae b. Dorsal vertebrae c. Lumbar vertebrae d. All of the above



5. Important feature of Potts spine is: a. Disk involvement b. Compression fracture

10. Which part of spine resists as an initial site of infection? a. Vertebral body b. Transverse process c. Disk d. Pedicle

ANSWERS 1. d 9. b

2. a 10. c

3. c

4. b

5. d

6. a

7. d

8. a

17 C H A P T E R

Recent Advances in the Field of Magnetic Resonance Imaging

FUNCTIONAL MAGNETIC RESONANCE IMAGING Functional magnetic resonance imaging or functional MRI (fMRI) is a functional neuroimaging procedure using magnetic resonance imaging (MRI) technology that measures brain activity by detecting associated changes in blood flow. It relies on the fact that cerebral blood flow and neuronal activation are coupled. This means when an area of the brain is in use, blood flow to that region also increases (Fig. 1). The primary form of fMRI uses the blood-oxygenlevel dependent (BOLD) contrast. It is used to map neural activity in the brain or spinal cord of humans

or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells. The procedure is similar to MRI but uses the change in magnetization between oxygen-rich and oxygen-poor blood as its basic measure. The resulting brain activation can be presented graphically by color-coding the strength of activation across the brain or the specific region studied (Figs. 2 and 3). Functional MRI is used both in the research world, and to a lesser extent, in the clinical world. It can also be combined and complemented with other measures of brain physiology such as electroencephalogram (EEG) and NIRS (near-infrared spectroscopy).

Fig. 1: Functional MRI of a patient during hand movement.

  Recent Advances in the Field of Magnetic Resonance Imaging  201

Fig. 2: Fluctuations in brain activity observed with fMRI.

Fig. 3: Neurophysiological basis of functional MRI.

202  Magnetic Resonance Imaging Functional MRI can be used to assess how risky brain surgery or similar invasive treatment is for a patient and to learn how a normal, diseased, or injured brain is functioning. Thus the brain is mapped to identify regions linked to critical functions such as speaking, moving, sensing, or planning. This is useful to plan for surgery and radiation therapy of the brain. fMRI is also used to anatomically map the brain and detect the effects of tumors, stroke, head, and brain injury, or diseases such as Alzheimer’s.

MAGNETIC RESONANCE SPECTROSCOPY Magnetic resonance spectroscopy (MRS), or nuclear mag­netic resonance (NMR) spectroscopy, is an analytical technique that can often be used to courtesy the magnetic resonance imaging (MRI) in the characterization of tissue. Both techniques use signals from hydrogen protons (1H), however MRI uses the information to create 2-dimensional images of the brain as compared to MRS that uses 1H signals to determine the relative concentrations of target brain metabolites. MRS is used to detect nuclei like carbon (13C), nitrogen (15N), fluorine (19F), sodium (23Na), phosphorus (31P) and hydrogen (1H), but significantly only the latter two are present in abundance in the body (Fig. 4). Though presently MRS is being used by scientists for medical research projects, however it can prove advantageous to the doctors in diagnosing and plan treatment protocols for various diseases.

Fig. 4: Distribution and appearance of the normal neurometabolites in a normal MR spectroscopy.

At present MRS is being used to investigate a number of diseases in the human body, notably cancer of breast, brain and prostate, epilepsy, Alzheimer’s disease, Parkin­ son’s disease and Huntington’s chorea (Table 1).

MAGNETIC RESONANCE ELASTOGRAPHY Magnetic resonance elastography (MRE) is a rapidly developing technology for quantitatively assessing the mechanical properties of tissue. The technology can be considered to be an imaging-based counterpart to pal­pation. The success of MRE as a diagnostic method is based on the fact that the mechanical properties of tissues are often dramatically affected by the presence of disease processes such as cancer, inflammation, and fibrosis. The technique essentially involves three steps: 1. Generating shear waves in the tissue 2. Acquiring MR images depicting the propagation of the induced shear waves 3. Processing the images of the shear waves to generate quantitative maps of tissue stiffness, called elastograms. Magnetic resonance elastography is already being used clinically for the assessment of patients with chronic liver diseases and is emerging as a safe, reliable, and noninvasive alternative to liver biopsy for staging hepatic fibrosis (Fig. 5). MRE is also being investigated for application to pathologies of other organs including the brain, breast, blood vessels, heart, kidneys, lungs, and skeletal muscle (Fig. 6).

POSITRON EMISSION TOMOGRAPHY– MAGNETIC RESONANCE IMAGING Positron emission tomography (PET)-magnetic resonance imaging (MRI) is a new hybrid imaging modality that combes two powerful diagnostic imaging tools. The indivi­dual strengths and weaknesses of the two imaging modalities are synergistic and complementary and hence either modality compensates for the limitations of the other modality by its individual advantages. Hence, PET-MRI combines the highest anatomical detail as well as biochemical and functional information provided by MRI with the metabolic, molecular, and physiologic information from PET.1 PET is a nuclear medicine functional imaging tech­ nique that produces a three-dimensional image of func­ tional processes going on in the body. Gamma rays emitted by a positron-emitting radionuclide (tracer)

  Recent Advances in the Field of Magnetic Resonance Imaging  203 Table 1: Metabolites and their associated anomalies detected by MR spectroscopy. Metabolite

Major peak resonance frequency

Associated anomaly

Choline

3.2 ppm

Demyelination, malignant tumors

Creatine and phosphocreatine

3.0 ppm

Cranial cerebral trauma

Lipids

0.9–1.5 ppm

Necrosis

Lactate

1.33 ppm

Ischemia, hypoxia, mitochondrial disorders

Lipid/lactate peak

0.9 ppm and 1.33 ppm

Tuberculoma

N-acetylaspartate (NAA)

2.02 ppm

Neuronal or axonal damage

Glutamate and glutamine

2.2 ppm and 2.4 ppm

Hyperammonemia, hepatic encephalopathy

Myoinositol

3.56 ppm

Alzheimer's, dementia, and HIV patients

(HIV: Human immunodeficiency virus).

Fig. 5: Assessment of hepatic fibrosis with magnetic resonance elastography.

entering the body is indirectly detected by the system. PET scan is helpful in assessing functional or metabolic status of tissue. If the biologically active molecule chosen for PET is fluorodeoxyglucose (FDG), an analog of glucose, the concentrations of tracer imaged will indicate tissue metabolic activity by virtue of the regional glucose uptake. Thus FDG is the most commonly used oncologic PET tracer. Though it is taken up in all metabolically active tissues uptake is much higher in tumor cells because

of elevated glucose transporter (GLUT) levels, elevated hexokinase levels and increased rates of glycolysis. Once taken up, it gets metabolically trapped as FDG-6-P, which is unable to undergo glycolysis/glycogen formation and is too polar to diffuse out of the cell (Fig. 7). Thus it gets “metabolically trapped”. When the positron created during the decay of the isotope in the FDG molecule meets an electron, they annihilate, resulting in the simultaneous release of two

204  Magnetic Resonance Imaging

Fig. 6: Acoustic driver system for magnetic resonance elastography.

Fig. 7: Metabolic trapping of fluorodeoxyglucose molecule in a malignant cell.

511 keV gamma photons traveling in nearly opposite directions. If we detect these pairs, we can determine the activity concentration using the density of the LOR (line of response) connecting the detection points. These radiations are then detected in the PET scanner and the image is superimposed on image formed by MRI scan, thus helping us located the malignant tissue (Figs. 8A to C).

The needs for whole-body imaging in the setting of PET-MRI are slightly different from the needs for wholebody standalone MRI in that image fusion with PET data will be desired and the acquisition time is a critical factor. Any cross-sectional data set can be fused with another, including MRI data from any acquired plane. However, to produce the highest quality of the fused images in each

  Recent Advances in the Field of Magnetic Resonance Imaging  205

A

B

C Figs. 8A to C: Schematic diagram showing annihilation reaction and its detection on scanner used in image reconstruction. (PET: Positron emission tomography).

plane, 3-dimensional imaging sequences are preferable in order to be able to guarantee the same high-image quality and detail in axial, sagittal, and coronal reconstructions. In this way, PET images can be directly fused and compared with MRI images. Positron emission tomography-magnetic resonance imaging has proved useful in evaluation of malignant lesions in different parts of body including head and neck cancers, lung cancers, pancreatic cancer, colorectal cancer, ovarian cancer, lymphomas, and various pediatric neoplasms (Fig. 9).

REAL-TIME MAGNETIC RESONANCE IMAGING

Fig. 9: Positron emission tomography-magnetic resonance imaging scan helps to localize a small neoplastic lesion in brain.

Real-time MRI refers to the continuous monitoring of moving objects in real time (Fig. 10). Recent advances in real-time MRI result in high-quality images with acquisition times of only approximately 30 milliseconds (Fig. 11). The technique employs a fast low-angle shot

206  Magnetic Resonance Imaging

Fig. 10: Real time MRI of normal swallowing.

Fig. 11: Real-time magnetic resonance imaging of the heart (arrow) with a measurement time of 33 milliseconds per image and 30 images per second.

  Recent Advances in the Field of Magnetic Resonance Imaging  207

A

B

C

Figs. 12A to C: (A) Anatomical location of the heart; (B) 3-dimensional image of the heart; and (C) comparision between normal and diseased (arrowheads) heart.     (RV: Right ventricle).

Fig. 13: Magnetic resonance imaging of fetal heart along three fetal body planes as well as cardiac axes.

208  Magnetic Resonance Imaging (FLASH) sequence with proton density, T1 or T2/T1 contrast and radial data encoding for motion robustness. Preliminary real-time examinations at a field strength of 3T range from joint dynamics, speaking, and swallowing to the 3-dimensional localization of objects in space. In particular, real-time MRI largely facilitates assessments of cardiovascular function and quantitative blood flow.

CARDIOVASCULAR MAGNETIC RESONANCE IMAGING Cardiovascular magnetic resonance imaging (CMR), some­ times known as cardiac MRI, is a medical imaging technology for the noninvasive assessment of the function and structure of the cardiovascular system. It is derived from and based on the same basic principles as MRI, but with optimization for use in the cardiovascular system. These optimizations are principally in the use of electrocardiogram (ECG) gating

and rapid imaging techniques or sequences. By combining a variety of such techniques into protocols, key functional and morphological features of the cardiovascular system can be assessed. Thus, this technique has proved to be useful in evaluation of heart function, infarct imaging, cardiac perfusion, and detecting heart muscle scar or fat without using contrast agents. It can also detect cardiac and pericardiac masses, pericardial diseases (pericardial effusion and constrictive pericarditis) as well as congenital anomalies of heart and diseases of aorta and great vessels (Figs. 12 and 13).

REFERENCE 1. Herrmann KA, Kohan AA, Gaeta MC, et al. PET/MRI: applications in clinical imaging. Current Radiology Reports. 2013;1(3):161-76.

MULTIPLE CHOICE QUESTIONS



1. What does fMRI mean? a. Functional MRI b. Fortis Memorial Research Institute c. First MRI d. Field MRI



5. What does MRS mean? a. Magnetic resonance imaging of spine b. Media recognition system c. Molecular recognition section d. Magnetic resonance spectroscopy



2. Principle of fMRI: a. To use BOLD contrast b. To detect brain function c. To detect motion d. To remove motion artifact



6. What is the function of MRS? a. Create 2-dimentional images of brain b. Determine the relative concentrations of brain target metabolites c. Remove motion artifacts d. Plan a surgery



3. Full form of BOLD: a. Bureau of Legal Dentistry b. Bleomycin, oncovin, lomustine, dacarbazine c. Blood-oxygen-level dependent d. Boeing online data system



7. Which signals does MRS use? a. 1H signals b. 13C signals c. 31P signals d. 23Na signals



4. What does NIRS mean? a. New Indian Resident Society b. Near-infrared spectroscopy c. Noninvasive Research System d. National Institute of Radiological Science



8. Uses of MRS: a. Detect Alzheimer’s b. Detect Huntington’s chorea c. Detect potential cancers d. All of the above

  Recent Advances in the Field of Magnetic Resonance Imaging  209

9. What does 2.02 ppm peak resonance frequency of N-Acetylaspartate represent? a. Tuberculoma b. Necrosis c. Alzheimer’s d. Neuronal or axonal damage

10. What is the use of MRE? a. Assess mechanical properties of tissues b. Detect brain activity c. Detect brain blood flow d. Angiography 11. In which organ pathologies MRE can be used? a. Brain b. Heart c. Kidneys d. All of the above 12. Which is the most commonly used oncologic PET tracer? a. Methionine b. Fluciclovine c. Fluorodeoxyglucose d. Acetate 13. What does real-time MRI refer to? a. Continuous monitoring of moving objects in real time b. Detect brain-blood flow c. Determine the relative concentrations of brain target metabolites d. Produce the highest quality of the fused images

14. The principle of CMR is same as: a. CT b. ECG c. MRI d. PET-MRI 15. A type of MRI examination that involves study of blood flow in the brain is: a. Functional MRI b. PET MRI c. MRS d. MRE 16. Which of the following diagnostic techniques can be used to best assess liver status? a. MRS b. MRE c. USG d. CT 17. The molecule used as an oncologic marker in case of PET-MRI is: a. GLUT b. FDG-6-P c. 18-FDG d. Glucose 18. In all neurological disorders there is decrease of NAA levels except: a. Canavan’s disease b. Alzheimer’s disease c. Parkinson’s disease d. Dementia 19. Sequence involved in real-time MRI imaging is: a. DWI b. FLAIR c. SWIRL d. FLASH 20. Cardiovascular MRI also known as: a. Cardiac phases MRI b. Cardiac MRI c. Cardiac timing MRI d. Cardioembolic MRI

ANSWERS 1. a 9. d 17. c

2. a 10. a 18. a

3. c 11. d 19. d

4. b 12. c 20. b

5. d 13. a

6. b 14. d

7. a 15. a

8. d 16. b

18 C H A P T E R

Magnetic Resonance Imaging Artifacts

INTRODUCTION1

Patient and Physiologic Motion

Magnetic resonance imaging (MRI) artifacts are numerous and give an insight into the physics behind each sequence. Some artifacts affect the quality of the MRI examination while others do not affect the diagnostic quality but may be confused with pathology. When encountering an unfamiliar artifact, it is useful to systematically examine general features of the artifact to try and understand its general class. These features include: • Type of sequence, e.g. fast spin echo (FSE), gradient, and volumetric acquisition • Direction of phase and frequency • Fat or fluid attenuation • Presence of anatomy outside the image field • Presence of metallic foreign bodies. Classification of the artifact type may give one an idea about how to try to fix it.

• Phase-encoded motion artifact • Entry slice phenomenon.

ARTIFACTS Many artifacts have a characteristic appearance and with experience they can be readily identified.

Magnetic Resonance Hardware and Room Shielding • • • • • • • •

Zipper artifact Herringbone artifact Zebra stripes Moire fringes Central point artifact Radiofrequency (RF) overflow artifacts Inhomogeneity artifacts Shading artifact.

Magnetic Resonance Software • Slice-overlap artifact (also known as cross-talk artifact) • Cross-excitation.

Tissue Heterogeneity and Foreign Bodies • Black boundary artifact • Magic angle effect • Magnetic susceptibility artifact –– Blooming artifact • Chemical shift artifact • Dielectric effect artifact.

Fourier Transformation and Nyquist Sampling Theorem • Gibbs artifact/truncation artifact • Zero-fill artifact • Aliasing/wrap around artifact. Artifacts are caused by a variety of factors that may be patient related, such as voluntary and physiologic motion, metallic implants, or foreign bodies. Finite sampling, k-space encoding, and Fourier transformation may cause aliasing and Gibbs artifact. Characteristics of pulse sequences may cause black boundary, Moire, and phaseencoding artifacts. Hardware issues may cause central point and RF overflow artifacts.

ZIPPER ARTIFACT2 It refers to a type of MRI artifact, where one or more spurious bands of electronic noise extend perpendicular to the frequency encode direction and is present in all images of a series. There are various causes for zipper artifacts in images. Most of them are related to hardware or software problems beyond the radiologist’s immediate control. The zipper artifacts that can be controlled easily are those that occur when the door is open during acquisition of images due to RF entering the scanning room from

 Magnetic Resonance Imaging Artifacts  211 electronic equipment (e.g. mobile devices or aircraft) and are being picked by the receiver chain of imaging subsystems. Radiofrequency from some radiotransmitters will cause zipper artifacts that are oriented perpendicular to the frequency axis of your image. Frequently, there is more than one artifact line on an image from this cause corresponding to different radio frequencies. Other equipment and software problems can cause zippers in either axis (Fig. 1).

Remedy • Make sure the MR scanner room-door is shut during imaging • Remove all electronic devices from the patient prior to imaging • If the artifact persists despite all nearby electronic equipment being turned off, it is possible that the RF shielding is compromised. –– This usually occurs at the contacts between the door and the jam and may need to be cleaned or repaired –– The penetration panel where the cables enter the room is another site to be checked.

Causes • Electromagnetic spikes by gradient coils • Fluctuating power supply • RF pulse discrepancies.

ZEBRA STRIPES/ARTIFACTS They appear as alternating bright and dark bands in a MRI image. The term has been used to describe several different kinds of artifacts causing some confusion. Artifacts that have been described as a zebra artifact include the following: • Moire fringes • Zero-fill artifact • Spike in k-space. Zebra stripes have been described associated with susceptibility artifacts. In computed tomography (CT), there is also a zebra artifact from 3-dimensional reconstructions and a zebra sign from hemorrhage in the cerebellar sulci. It, therefore, seems prudent to use “zebra” with a term like “stripes” rather than “artifacts”.

MOIRE FRINGES4

Herringbone artifact, also called as crisscross artifact or corduroy artifact, is an MRI artifact and it appears as a fabric of herringbone. The artifact is scattered all over the image in a single slice or multiple slices (Fig. 2).

They are an interference pattern most commonly seen when doing gradient echo (GE) images with the body coil. Because of lack of perfect homogeneity of the main magnetic field from one side of the body to the other, aliasing of one side of the body to the other results in superimposition of signals of different phases that

Fig. 1: Zipper artifact.

Fig. 2: Herringbone artifact.

HERRINGBONE ARTIFACT3

212  Magnetic Resonance Imaging alternatively add and cancel. This causes the banding appearance and is similar to the effect of looking through two screen windows (Fig. 3). The central point artifact is a focal dot of increased signal in the center of an image. It is caused by a constant offset of the DC voltage in the receiver. After Fourier transformation, this constant offset gives the bright dot in the center of the image as shown in the diagram. The axial MRI image of the head shows a central point artifact projecting in the pons in the center of the image.

Correction and Prevention • Repeating the sequence may get rid of the artifact • Maintain a constant temperature in scanner and equipment room for receiver amplifiers • Software to estimate DC offset and to adjust the data in k-space • Call service engineer for recalibration.

RADIOFREQUENCY OVERFLOW ARTIFACT5 It causes a nonuniform and washed-out appearance to an image. This artifact occurs when the signal received by the scanner from the patient is too intense to be accurately digitized by the analog-to-digital converter. Autoprescanning usually adjusts the receiver gain to prevent this from occurring but if the artifact still occurs, the receiver gain can be decreased manually. Postprocessing methods also exist but may be time consuming (Fig. 4).

Fig. 3: Moire fringes.

Shading artifact in MRI refers to loss of signal intensity in one part of the image, leading to dark shading in this portion of the image.

Causes • Uneven excitation of nuclei within the field; due to RF pulses applied at flip angles other than 90° and 180° • Abnormal loading of coil or coupling of coil at a point (as with a large patient whom touches one side of the coil) • Inhomogeneity in the magnetic field • Overflow of analog-to-digital converter.

Axis • Frequency encoding • Phase encoding.

Remedy • Load the coil correctly • Use the proper-size coil for patient size and the examined part • Prevent the patient touching the coil (you can use foam pads between patient and coil) • Shimming to reduce inhomogeneity of the magnetic field • Use the proper scanning parameters to set proper amplitude of applied RF pulses (less amplification to avoid analog-to-digital converter overflow). In MR imaging, zipper artifact refers to a type of MRI artifact where one or more spurious bands of electronic

Fig. 4: Radiofrequency overflow artifact.

 Magnetic Resonance Imaging Artifacts  213 noise extend perpendicular to the frequency encode direction and are present in all images of a series. There are various causes for zipper artifacts in images. Most of them are related to hardware or software problems beyond the radiologist’s immediate control. The zipper artifacts that can be controlled easily are those that occur when the door is open during acquisition of images due to RF entering the scanning room from electronic equipment (e.g. mobile devices or aircraft) and are being picked by the receiver chain of imaging subsystems. Radiofrequency from some radiotransmitters will cause zipper artifacts that are oriented perpendicular to the frequency axis of your image. Frequently, there is more than one artifact line on an image from this cause corresponding to different radiofrequencies. Other equip­ ment and software problems can cause zippers in either axis.

Remedy • Make sure the MR scanner room-door is shut during imaging • Remove all electronic devices from the patient prior to imaging • If the artifact persists despite all nearby electronic equipment being turned off, it is possible that the RF shielding is compromised –– This usually occurs at the contacts between the door and the jam and may need to be cleaned or repaired –– The penetration panel where the cables enter the room is another site to be checked.

SLICE-OVERLAP ARTIFACT It is also known as cross-talk artifact, is a name given to the loss of signal seen in an image from a multiangle and multislice acquisition, as is obtained commonly in the lumbar spine. It should not be confused with crossexcitation, which although similar in causation, is not due to angled images. If the slices obtained at different disk spaces are not parallel, then the slices may overlap. If two levels are done at the same time, e.g. L4-5 and L5-S1, then the levelacquired second will include spins that have already been saturated. This causes a band of signal loss crossing horizontally in your image, usually worst posteriorly.

Fig. 5: Slice-overlap Artifact.

The dark horizontal bands in the bottom of the following axial image through the lumbar spine demonstrate this artifact. As long as the saturated area stays posterior to the spinal canal, it causes no harm (Fig. 5).

CROSS-EXCITATION ARTIFACT It is a type of MRI artifact and refers to the loss of signal within a slice due to pre-excitation from RF pulse meant for an adjacent slice. The frequency profile of the RF pulse is imperfect; this means that during slice selection there is some degree of excitation of the adjacent slices as well. If that adjacent slice is imaged during the same TR (i.e. multislice imaging) or soon after (i.e. imaging without leaving a gap), it will be partially saturated, to begin with, and the resulting signal will be reduced. This phenomenon is more conspicuous in inversion recovery (180°) sequences.

Remedy • Leaving a minimum gap of one-third slice thickness when imaging contiguous slices • Interleaving between slices • Employing 3-dimensional imaging, if volume imaging is required • Using optimized pulse sequences that have a time penalty of a higher minimum TE and reduced number of slices for a given TR.

214  Magnetic Resonance Imaging

PHASE-ENCODED MOTION ARTIFACT It is one of many MRI artifacts and occurs as a result of tissue/fluid moving during the scan and manifests as ghosting in the direction of phase encoding, usually in the direction of short axis of the image (i.e. left to right on axial or coronal brains and anterior to posterior on axial abdomen). These artifacts may be seen from arterial pulsations, swallowing, breathing, peristalsis, and physical movement of a patient. When projected over anatomy, it can mimic pathology and needs to be recognized. Motion that is random such as the patient moving produces a smear in the phase direction. Periodic motion, such as respiratory or cardiac/vascular pulsation, produces discrete and well-defined ghosts. The spacing between these ghosts is related to the TR and frequency of the motion. Motion artifacts can be distinguished from Gibbs or truncation artifacts because they extend across the entire field of view (FOV), unlike truncation artifacts that diminish quickly away from the boundary causing them. Ways of identifying phase artifact include: • Identifying known moving/flowing structures and noting that the artifact is in line with them (horizontal or vertical depending on phase encoding orientation) • Matching shape of ghost to that of flowing vessel (e.g. round pseudolesion due to aorta ghost) • Wide windowing to see repetitive ghost beyond confines of anatomy • They can be distinguished from Gibbs or truncation artifacts because they extend across the entire FOV, unlike truncation artifacts that diminish quickly away from the boundary causing them (Fig. 6).

Remedy Solutions to phase mismapping include: • Cardiac/respiratory gating • Spatial presaturation bands placed over moving tissues (e.g. over the anterior neck in sagittal cervical spines) • Spatial presaturation bands placed outside the FOV, especial before the entry or after the exit slice for reducing ghosting from vascular flow: arterial and venous • Scanning prone to reduce abdominal excursion • Switching phase and frequency directions • Increasing the number of signal averages • Shorten the scan time when motion is from patient moving.

Fig. 6: Phase-encoded motion artifact.

Entry Slice Phenomenon It occurs when unsaturated spins in blood first enter into a slice or slices. It is characterized by bright signal in a blood vessel (artery or vein) at the first slice that the vessel enters. Usually, the signal is seen on more than one slice, fading with distance. This mechanism is used in a positive fashion to generate flight MR angiograms. This artifact has been confused with thrombosis with disastrous results. The characteristic location and, if necessary, the use of GE flow techniques can be used to differentiate entry slice artifacts from occlusions. Spatial saturation bands place before the first slice and after the last can be used to eliminate this artifact.

BLACK BOUNDARY ARTIFACT India ink artifact is an artificially created black line located at fat-water interfaces, such as those between muscle and fat. This results in a sharp delineation of the muscle-fat boundary that is sometimes visually appealing but not an anatomical structure (Fig. 7).

Remedy To avoid this artifact: • TE’s close to 4.5 milliseconds, 9 milliseconds, and 13.6 milliseconds should be chosen • Fat suppression can be used • A spin echo (SE) sequence instead of GE will also eliminate the artifact. The magic angle is an MRI artifact, which occurs on sequences with a short TE [less than 32 milliseconds;

 Magnetic Resonance Imaging Artifacts  215

Fig. 7: Black boundary artifact.

Fig. 8: Magic angle artifact.

T1W sequences, proton density (PD) sequences, and GE sequences]. It is confined to regions of tightly bound collagen at 54.74° from the main magnetic field (B0) and appears hyperintense, thus potentially being mistaken for tendinopathy (Fig. 8).

Typical sites include: • Proximal part of the posterior cruciate ligament (PCL) • Peroneal tendons as they hook around the lateral malleolus • Cartilage can also be affected, e.g. femoral condyles • Supraspinatus tendon • Triangular fibrocartilage complex (if the patient is imaged with the arm elevated) • Infrapatellar tendon at the tibial insertion. It appears that at 3.0T the effects are reduced. Other nonpathologic causes of high signal within tendons include near tendon insertions, and/or where the tendon normally fans out or merges with other tendons.

Normally In tightly-bound collagen, water molecules are restricted usually causing very short T2 times and accounting for the lack of signal.

Artifact When molecules lie at 54.74°, there is lengthening of T2 times with corresponding increase in signal. Thus in short-TE sequences, the T2 signal does not decay significantly before the scanner picks up the signal. On the other hand, in long-TE sequences (like T2WI) by the time, the scanner picks up the signal, T2 signal has already decayed. The reason for this change is due to quantum mechanics: in the set of equations that describe the interaction of spins (their Hamiltonian), there are several terms that are orientation-dependent. Normally, these orientations are averaged over as protons tumble around thermally, but in sites with long-range order these terms can be important. In the case of structured collagen, lot of water binds to the outside of the protein and, therefore, exhibits an orientation-dependent effect.

Remedy • Tends to occur only on short-TE sequences (e.g. T1, GE, PD), sequences with a longer TE (e.g. T2 including FSE T2) can be used to avoid this artifact.

MAGNETIC SUSCEPTIBILITY ARTIFACTS (SUSCEPTIBILITY ARTIFACT) It refers to a variety of MRI artifacts that share distortions or local signal change due to local magnetic field inhomogeneities from a variety of compounds. They are especially encountered while imaging near metallic orthopedic hardware or dental work, and result from local magnetic field inhomogeneities introduced by the metallic object into the otherwise homogeneous external magnetic field B0. These local magnetic field

216  Magnetic Resonance Imaging inhomogeneities are a property of the object being imaged, rather than of the MRI unit. A common susceptibility-related artifact, deliberately sought to make small lesions more conspicuous, is the blooming artifact (Fig. 9).

Types of Magnetic Susceptibility In terms of magnetic susceptibility, most materials can be classified as diamagnetic, paramagnetic, super­ paramagnetic, or ferromagnetic.

Diamagnetic • Water is considered (weakly) diamagnetic.

Paramagnetic Paramagnetic materials, which have unpaired electrons, concentrate local magnetic forces and thus increase the local magnetic field, i.e. have increased magnetic susceptibility.

Superparamagnetic Superparamagnetic materials contain particles with a much stronger magnetic susceptibility than that of paramagnetic materials, e.g. SPIO (superparamagnetic iron oxide) has been used in liver imaging.

Ferromagnetic Ferromagnetic materials contain large solid or crystalline aggregates of molecules with unpaired electrons exhibit “magnetic memory”, by which a lingering magnetic field is created after their exposure to an external magnetic field.

Examples of ferromagnetic metals include iron, nickel, and cobalt, all of which distort magnetic fields, thereby causing severe artifacts on MR images.

CHEMICAL SHIFT ARTIFACT OR MISREGISTRATION6 It is a type of MRI artifact. It is a common finding on some MRI sequences and used in MRS. Chemical shift is due to the differences between resonance frequencies of fat and water. It occurs in the frequency encode direction where a shift in the detected anatomy occurs because fat resonates at a slightly lower frequency than water. Essentially, it is due to the effect of the electron cloud to a greater or lesser degree shielding the nucleus from the external static magnetic field (B0). The Larmor frequency, which determines the frequency at which a particular nucleus resonates, is established at the nucleus and, therefore, different tissues will have slightly different Larmor frequencies depending on their chemical composition. In addition to mismapping, GE sequences can show another type of chemical shift induced artifact known as the black boundary or India ink artifact. In the artifact, a black line is seen in all directions at fat-water interfaces. In pixels with roughly equal amounts of fat and water, the fat and water spins are 180 out of phase at certain echo times because of their chemical shift or frequency difference causing cancellation of signal. These effects can be used to confirm, for example, the presence of fat in a lesion. • Chemical shift increases with magnetic field strength • Chemical shift increases with decreasing gradient strength • Chemical shift depends upon the bandwidth; narrower the bandwidth higher is the chemical shift. Increasing the bandwidth will decrease the artifact • Fat-suppressed imaging can be used to eliminate the chemical shift misregistration and the black boundary artifact • Use of a SE sequence instead of a GE can eliminate the black boundary artifact but not chemical shift misregistration.

DIELECTRIC EFFECT ARTIFACT Fig. 9: Magnetic susceptibility artifacts.

It is an MRI artifact encountered most often on body MRI with 3T units.

 Magnetic Resonance Imaging Artifacts  217

Artifact At 3T, the RF wavelength measures 234 cm in air and the speed and wavelength of the RF field are shortened to ~26 cm within the body as a result of dielectric effects. However, this 26 cm FOV is approximately the crosssectional diameter of most body imaging studies. With patient abdominal diameters that exceed the RF wavelength (e.g. patients with cirrhosis and ascites or pregnant patients), constructive and destructive interference patterns may emerge. In body MRI, this may lead to darkening/shading at the center of the image. At 7.0T, the RF wavelength in tissue decreases to ~11 cm.

Improvement • Switch imaging to a less than 3.0T system • Drain ascites before imaging a patient with cirrhosis to decrease the chance of the artifact occurring.

Aliasing in Magnetic Resonance Imaging Also known as wrap-around is a frequently encountered MRI artifact that occurs when the FOV is smaller than the body part being imaged. The part of the body that lies beyond the edge of the FOV is projected onto the other side of the image. This can be corrected, if necessary, by oversampling the data. In the frequency direction, this is accomplished by sampling the signal twice as fast. In the phase direction, the number of phase-encoding steps must be increased with a longer study as a result. However, if the FOV and matrix size (phase-encoding steps) are increased and simultaneously number of excitations (or number of signal averages) reduced to half, the imaging time can be kept constant with correction of aliasing.

Remedy Aliasing in MRI can be compensated for by: • Enlarging the FOV • Using presaturation bands on areas outside the FOV • Antialiasing software

• Switching the phase and frequency directions • Use a surface coil to reduce the signal outside of the area of interest.

CONCLUSION • Artifacts in MR images are an inevitable truth • MRI artifacts occur because one or more of the assumptions underlying the imaging principles have been violated • Some can be reduced while others can be totally eliminated • Artifact correction methods usually involve one or more of the following: –– Hardware calibration –– Scanning parameter optimization –– Special pulse sequence design –– Signal and image postprocessing • By understanding the mechanism of their production and their effects on the final image, technologists should considerably try to minimize these artifacts with the use of reduction techniques • Ideally, we want all image artifacts to be below the level of user’s perception. Artifact correction is an active area of research today and will continue to be in the future as advances in MRI technology reveal new image information and new kinds of artifacts.

REFERENCES 1. Anne B. Planning and Positioning in MRI. Australia: Churchill Livingstone; 2011. 2. Allisy-Roberts P, Williams J, Farr RF. Farr’s Physics for Medical Imaging. WB. Saunders Company; 2007. 3. Westbrook C, Roth CK, Talbot J. MRI in Practice. WileyBlackwell; 2011; pp. 225-30. 4. McRobbie DW, Moore EA, Graves MJ. MRI from Picture to Proton. Cambridge University Press; 2007; p. 215. 5. Hashemi RH, Bradley WG, Lisanti CJ. MRI. Lippincott Williams & Wilkins; 2010; pp. 185-90. 6. From mritutor.org, available at http://www.mritutor.org/ mritutor/zipper.htm.

218  Magnetic Resonance Imaging

MULTIPLE CHOICE QUESTIONS



1. In the presence of a uniform magnetic field, hydrogen protons: a. Line up along the field and rotate around its axis b. Line up along the field and process around its axis c. Remain oriented mostly randomly and process around the field axis d. Are not affected by the magnetic field



2. SNR in MRI is improved by increasing: a. Resolution b. Bandwidth c. Gradient strength d. Acquisition time



3. Increasing bandwidth causes: a. Worsened chemical shift artifact b. Worsened SNR c. Worsened metal hardware artifacts d. Longer echo acquisition time









4. Which of the following is true about reducing phase-encoding steps? a. Increasing k-space spacing ≥ worse resolution b. Dropping peripheral k-space lines (dropping scan percentage) ≥ smaller FOV c. Half-Fourier acquisition ≥ worse resolution d. Worse SNR 5. The spacing of lines in k-space corresponds to: a. Resolution b. Number of excitations c. Matrix size d. Field of view 6. Aliasing refers to the mathematical phenomenon of: a. Frequency or phase misregistration because of signal undersampling b. Pixel misregistration related to gyromagnetic differences c. Pixel blurring caused by lack of sampling high frequencies d. Pixel misregistration because of patient motion 7. Radiofrequency contamination artifact causes: a. “Ghosting” of multiple copies of structures b. Diagonal lines across the image c. Random noise across the image d. Line(s) parallel to the phase-encoding axis



8. Motion artifact is caused by: a. Long time in-between acquisition of points in k-space along the frequency-encoding direction b. Long time in-between acquisition of points in k-space along the phase-encoding direction c. Frequency shifts in protons related to velocity d. Dephasing of protons related to velocity



9. Radiofrequency contamination artifact is best addressed by: a. Checking or replacing the receiver coils b. Checking or replacing the transmit coils c. Shimming the magnet d. Checking or replacing room and door shielding

10. You are attempting to perform a liver MRI to evaluate for metastatic disease and a copy (ghost) of the aorta appears over segment 3. What is the best way to remove this artifact? a. Swap phase and frequency encoding directions b. Phase oversampling c. Increase bandwidth d. Give intravenous contrast 11. Which of the following is not a cause of Herringbone artifact? a. Electromagnetic spikes by gradient coils b. Fluctuating power supply c. RF pulse discrepancies d. Inhomogeneity in the magnetic field 12. Which is not a type of magnetic susceptibility? a. Diamagnetic b. Paramagnetic c. Epoxymagnetic d. Supermagnetic 13. For assessment of artifacts, following features are to be considered except: a. Direction of phase and frequency b. Fluid or fluid attenuation c. Presence of plastic foreign body d. Presence of anatomy outside the magnetic field 14. Moire fringes artifact is caused due to: a. MR software b. MR hardware and room shielding c. Tissue heterogeneity and foreign bodies d. Fourier transformation and Nyquist sampling theorem

 Magnetic Resonance Imaging Artifacts  219 15. What is the appearance of an image in a RF overflow artifact? a. Nonuniform and washed-out appearance b. Uniform and washed-out appearance c. Uniform and solid appearance d. Nonuniform and solid appearance 16. Which of the following can be employed as a remedy for cross-excitation artifact? a. Switching phase and frequency directions b. Shorten the scan time when motion is from patient moving c. Interleaving between slices d. Shimming to reduce inhomogeneity of the magnetic field 17. What is Zipper artifact? a. Alternating bright and dark bands in an MRI image b. One or more spurious bands of electronic noise extending perpendicular to the frequency encode direction and present in all images of a series

c. Interference pattern most commonly seen when doing GE images with the body coil d. Loss of signal seen in an image from a multiangle and multislice acquisition

18. When does entry slice phenomenon occur? a. Saturated spins in blood first enter into a slice or slices b. Unsaturated spins in blood first enter into a slice or slices c. Unsaturated spins in blood first exits from a slice or slices d. Saturated spins in blood first exits from a slice or slices

19. Which of the following is not a ferromagnetic material? a. Iron b. Nickel c. Cobalt d. Lead 20. Artifacts due to tissue heterogeneity and foreign bodies include the following except: a. Magic angle effect b. Black boundary artifact c. Zero-fill artifact d. Chemical shift artifact

ANSWERS 1. c 9. d 17. b

2. d 10. a 18. b

3. b 11. d 19. d

4. d 12. c 20. c

5. d 13. c

6. a 14. b

7. d 15. a

8. b 16. c

Index Page numbers followed by f refer to figure and t refer to table.

A Abdomen 40, 48, 51, 56, 113f noncontrast 51 Abdominal procedures 93 Abdominal wall collaterals 168 Ablation therapy 91 Abscess 128, 158, 190f bacterial 160 collection of 192f Acoustic driver system 204f Acromion, types of 177, 178f Adamantinoma 141 Adrenal mass 53, 121 Adrenoleukodystrophy 151f Air embolus 43 Alcohol 164 abuse 162 Alcoholism 73, 160, 161 Alexander disease 151, 151f Allergic reactions 96 Allergy 39 Alpha radiation 3 Anaplastic astrocytoma 155 Anesthesia injection 91 Aneurysm 38 Aneurysmal bone cyst 141, 145, 145f Angiogram, three-dimensional reconstruction of 95f Angiography, digital subtraction 5 Angiosarcoma 141 Ankle 126 coil 113f Antitrypsin deficiency, alpha-1 160 Aorta 172 Aortic aneurysm 56, 121 abdominal 172f Apnea 38 Appendicitis 51 Appetite, loss of 20 weight 19 Arachnoid layer 152 Arch of aorta 95f Arnold-Chiari malformation 148 Artefact cupping 100, 101 partial volume 102, 103f

Arterial hematogenous 197 Arteriovenous malformation 67f Arthritis, stage of 190, 191 Asbestosis 69 Ascites 168 Aspergillosis 150 Astrocytoma 154, 155t low-grade 155 Ataxia 38 Atomic Energy Regulatory Board 17 Atrophy 39 Attenuation correction artifacts 84 Autoimmune disease 150 Autosomal dominant polycystic kidney disease 76, 158 Avascular necrosis 121 Axial computed tomography scan 67f, 69f, 70f bone window 61f of abdomen 62f Axial section of computed tomography scan 65f-68f

B Barium 49 sulfate 13, 129 Basal ganglia, level of 139f Bile duct, common 157, 165 Biliary cirrhosis 73, 160 tract 166f disease, chronic 163 Biopsy, fine-needle 91 Biventricular cardiac failure 168 Bleeding, internal 128 Blood oxygen-level dependent 200 vessels 141 Bone 121 cyst 145 of calcaneum 145f forming tumors 142 infection of 190 involvement 38 island 141 marrow

disorder 121 edema-like lesions 182 scans 3 tumors 141 benign 142 classification of 141t malignant 146 Bony origin 141 Bowel mass, small 49 obstruction, acute small 49 Bowtie filter 31f Brachial plexus avulsion 121 Brain 68, 113f, 122, 149f, 150f abnormalities, morphologic 38 abscess 67, 68f adult 121 computed tomography 38 hematomas 65 herniation 38 infarcts 121 infections 121 tumors 67 Brainstem 155 Breast cancer 121 coil 113f Breath 50 Bridging cortical veins, rupture of 152 Brodie’s abscess 193 Bronchogenic carcinoma 69 Bronchogenic cyst 70 Budd-Chiari syndrome 168

C Calcification, evaluation of 38 Calcium fluoride 24 oxalate 76 phosphate 76 pure 76 Callososeptal interface 150 Canavan’s disease 151, 151f Cancer detection 84 staging 84

222  Textbook of Radiology for CT and MRI Technicians with MCQs Carcinoma ductal 164f gallbladder 167f Cardiac anatomy 85t Cardiac arrest 12 Cardiac computed tomography 61f reconstruction images 61f Cardiac imaging 14 Cardiovascular magnetic resonance imaging 208 Carotid angiography 96 Carotid arteries 133f Carpal tunnel syndrome 183 Cartilage forming tumors 142 Cell carcinoma, nonsmall 69 carcinoma, small 69 malignant 204f tumors, malignant round 142 Central nervous system 148 Cerebellar herniation 149f Cerebellum 155 Cerebral arteriovenous malformation 67 artery, middle 133f hemisphere white matter 155 parenchyma 66f white matter 155 Cerebrospinal fluid 65 Cervical 112f canal 149f cancer 51 spine 124, 124f, 186 spondylosis 185f Chemotherapy 38, 39 Chest 45, 122 computed tomography 37 pain, acute 40 Cholangiocarcinoma 72, 73, 73f Cholangitis, ascending 165 Cholecystitis, chronic 167 Choledocholithiasis 165 Cholelithiasis 72, 166 Choline 203 Chondroblastoma 141, 144 Chondroma 141 Chondromyxoid fibroma 141 Chondrosarcoma 141, 146 of tibia 146f Chordoma 141 Choroid plexus 156f papillomas/carcinomas 154 tumors 155 Circle of Willis 134f

Cirrhosis 162, 168 of liver 168f Coal workers pneumoconiosis 69 Coccidioidomycosis 149 Cochlear implant 39 Cochlear otosclerosis 40 Collimator 31, 32f Collins’ sign 166 Colloidal vesicular 66 Computed tomography 3, 12, 41, 45, 48, 71-74, 76, 80, 89, 90, 100 anatomy 59 angiography 86, 95 artifacts 100 axial image 75f, 77f axial section 59f of abdomen 62f bone reconstruction of bilateral hip joint 64 cervical spine 63f elbow joint 63f lower limb bones 64 right shoulder joint 63f colonography 55 contrast media, intravenous 13 contrast-enhanced 171f coronal section 62f coronary angiography 85 cystography 52 dual energy 82, 83f enterography 55 images 37, 89f interventions 93t methodology 29 multidetector 81 multiple detector 81 noncontrast 73f number 32 over conventional radiography advantages of 33 disadvantage of 34 over magnetic resonance imaging advantages of 34 disadvantage of 34 pathologies, basic 65 pelvis 56 portography 98 pressure injectors 41 scan 7, 45, 66-70, 75f coronal section of 66f urography 54 use of 37 Computed tomography-guided biopsy of mediastinal mass 91f

biopsy of vertebral mass 92f interventions 92 Computerized axial tomography scan 7 Cone-beam 104 computed tomography 81f scanner 80 Congenital anomalies 38, 121 biliary atresia 73, 160 defects 39 lesions 38 Connective tissue tumors 144 Constrictive pericarditis 172, 173f Contrast agents, positive 14 Contrast enhanced computed tomography 74 of cholangiocarcinoma 72f Contrast enhancement of paraumbilical vein 168 Contrast media 11, types of extravasation of 11 positive 11 Contrast medium 39 Contrast, role of 11 Cord, compression of 185f Coronary artery 61f bypass graft 86 disease, signs of 85 motion artifacts 86 Coronary calcium, evaluation of 85 Coronary venous collaterals 168 Corpus callosum, splenium of 152f Cortical dysphasia 38 Cosmic rays 17 Cranial cerebral trauma 203 fossa, posterior 59f nerve dysfunction 38 Craniosynostosis 38 Creatine 203 Cruciate ligament 181f anterior 179, 181f injury 179 normal posterior 181f posterior 181 tear, anterior 181 Cullen sign 163 Cyst 164 benign 170 hypointense 159f Cystic angiomatosis 141 Cystic fibrosis 163 Cystic masses 170 Cystic neoplasm 164

 Index 223 Cystic nerve compression 40 Cystic teratoma, mature 171f Cystine 76 Cytomegalovirus 150

D Dandy-Walker malformations 148 Dawson’s finger 150f Defecography 129f Dementia 39, 121, 203 Demyelinating diseases 121 Dental radiography 4 Desmoplastic fibroma 141 Diabetes mellitus 162 severe 161 Diarrhea 19, 20, 49 Diatrizoate meglumine 49 Diffuse liver disease 160 parenchyma 162f Diffuse soft tissue edema 193f Diplopia 38, 39 Discitis 197f bacterial 198f Disk bulge 186 degeneration 185 herniation 186 Distal extrahepatic 72 Diverticulitis 51 Double duct sign 75f, 164 Drug 161 toxicity 38 Dyslipidemia 162 Dyspnea 171f

E Echo sequences, disadvantages of gradient 115 Elbow 113f Electroencephalogram 200 Electromagnetic radiation 17 Electron beam tomography 85 Encephalitis 38, 150 Enchondroma 142 of proximal phalanx 143f Endocrine 75, 164 Endometrial cancer 51 Endoscopic retrograde cholangiopancreatography 3 Enema 13 Energy resolution, good 83

Enteroclysis 128 Enterography 46t, 128 Ependymomas 154 Epicondyle of tibia, medial 144f Epidural hematoma 65, 65f soft tissue component 196f Epilepsy 121 Epistaxis 38 Epithelium 141 ductal 164 Esophageal collaterals 168 Ewing’s sarcoma 146 Exocrine 164 Exogenous steroid intake 162 Extension 186 Extradural hemorrhage 151

F Face 113f Facial bone 39 Facial trauma 38 Familial adenomatous polyposis syndrome 167 Fast spin echo 117 Fat suppression 119 Fatty liver 160 of pregnancy, acute 162 Femur lower end of 144f, 147f osteosarcoma of distal 146f shaft of 146f Fever 20 of unknown origins 121 Fibromatosis 141 Fibro-osseous disease 38 Fibrosarcoma 141 Fibrous cortical defect 141, 144, 144f dysplasia 144 of tibia 144f histiocytoma 141 tumors 144 Filtered back projection 33, 84 Flattened median nerve 183f Flexion 186 Flexor tendon tenosynovitis 184f Fluid attenuated inversion recovery 116 Fluorodeoxyglucose 203 molecule 204f Fluoroscopy 3 Food toxins 73, 160 Foot 113f

Foramen magnum 148f Fracture 40, 121

G Gadolinium chelates 129 Gallbladder 166 carcinoma 71, 167 indicating calculi 166f Gallstones 162 Gamma radiation 3 Ganglioneuroma 187 Gangliocapsular region 139f Gastrointestinal bleeding 14, 49 tract 11, 195 Gaucher’s disease 164 Genitourinary tract 76 Giant cell containing 141 tumor 141, 145 malignant 141 of medial condyle of femur 145f Glenoid labrum 121 Glioblastoma multiforme 155 Glioma 154 low-grade 67f Glomerular filtrate rate 47 Glomus tumor 141 Glucose transporter 203 Glutamate 203 Glycogen storage diseases 162 Gradient coils 109, 110 placement of 111f Gradient echo sequence 115 advantages of 115 Gram-negative organisms 197 Granular nodular 66 Graves’ disease 39 Grey-Turner’s sign 163

H Haemorrhage signs of 163 surgical treatment of 38 Hair, fall of 20 Head 65 computed tomography 45, 47, 47t of pancreas 164f trauma 121 acute 38 Headache 38 acute 121 severe 121

224  Textbook of Radiology for CT and MRI Technicians with MCQs Hearing loss 40 without atresia 40 Heart 172 anatomical location of 207f four-chamber view of 61f function of 172f pacemakers 121 Hemangioma 141, 144, 158 Hemangiomatosis 141 Hematuria 45 Hemochromatosis 160 Hemorrhage 20, 38 Hemorrhagic lesions 38 Hepatic cysts 158 encephalopathy 203 fibrosis 203f hemangioma 73, 158 veno-occlusive disease 168 venous malformations 73 Hepatitis 161 B infection 72, 160 C infection 72, 160 chronic 162 Hepatobiliary contrast 160 system 71, 157 Hepatocellular carcinoma 52, 72, 160 Hereditary pancreatitis 163, 164 Herniated nucleus pulposus 186f Herpes simplex virus 150 Heterogeneous hypointense soft tissue mass 167f intensity mass 154f masses 71f mediastinal mass 171f Hip 113f joint axial section, bilateral 136f infection 190f tuberculosis of 190 Horn of medial meniscus, posterior 180f Hounsfield scale 33t Hounsfield unit 32 Hydrocephalus 38, 39 Hyperammonemia 203 Hypercalcemia 162 Hyperintense 162 temporal lobe 150f Hyperintensity, deep periventricular 152f Hyperparathyroid brown tumor 141 Hyperparathyroidism 163 Hypertriglyceridemia 162 Hypointense filing defects 166f subchondral cysts 182f

Hypotension 12 Hypoxia 203 Hypoxic-ischemic encephalopathy 153, 154f

I Iliac angiography 97 Inflammation acute 38 chronic 38 Inflammatory bowel disease 161, 167 granuloma 67f Injury 121 patterns, common 186 Insulin pumps 121 resistance 162 Interstitial lung disease 40 Intestine wall 128 Intracranial haemorrhage 151 acute 38 infections 148 metal clips 121 neoplasm 154 pressure 38 Intraductal papillary mucinous neoplasm 164 Intrahepatic biliary dilatation 71 radical dilatation, proximal 167f Intraosseous ganglion 142 Intraparenchymal hemorrhage 65, 66f Intravenous hyperalimentation 162 routes, common 42 Iodine 39 Ionic dimers 13 Ionizing radiation 3 Iron, metalloporphyrins of 14 Ischemia 203 Ischemic stroke 65 right 66f Islets of Langerhans 75 Ivory osteoma 141

J Jaundice 160 obstructive 165 Joint effusion 182

K Kidney 45 Knee 112f, 123 joint 144f, 179 magnetic resonance imaging 179 tuberculosis of 191 Krabbe’s/Globoid leukodystrophy 151

L Lacrimal duct 40 Lactate 203 Leg 112f Leiomyoma of uterus 121 Leishmaniasis 164 Leukemias 142 Limb of internal capsule, posterior 152f Linear attenuation coefficient 32 Lipids 203 Lipoma 141, 145, 158 Liposarcoma 141 Listeria monocytogenes 150 Liver 45, 157 abscess drainage 89f anatomy, classification of 157f lesions 121 parenchyma 158 segments of 158f triple phase 52 Lobes of lungs, bilateral 69f Local irradiation 19 Low density barium 129 Low osmolarity contrast 13 Low signal intensity 198 Low-attenuation contrast agents 13 Lumbar spine 125, 125f Lumbar vertebra, typical 61f Lung diseases, occupational 69 mass, biopsy of 90f Lymphadenopathy 71, 121 Lymphocytic meningitis 149 Lymphomas 142, 164, 170

M Magnet, types of 110, 110t Magnetic resonance angiography 14, 172 cholangiopancreatography 4, 127, 164, 166f elastography 202, 203f, 204f spectroscopy 202

 Index 225 Magnetic resonance imaging 3, 4, 8, 37, 109, 115, 121, 142, 142f, 149f, 150, 151f-156f, 158, 158f, 159f, 162, 162f, 163, 163f, 164, 164f-168f, 170, 191, 192, 193, 193f, 195, 197f, 198f, 199, 200, 202 anatomy 132 ankle joint 143f axial sections 161f brain axial sections 153f contrast agents 13, 14 flair 152f full thickness tear 175 functional 200 of fetal heart 207f of heart, real-time 206f of lower end of femur 192f of lumbar spine 197f pathologies, basic 141 physics 109 real-time 205 scan 170f, 205 spine 185f standard views 175 techniques sequences 158f thorax 170 Magnets, permanent 109 Malabsorption 49 Malaise 20 Malaria 164 Malnutrition 161 Mammography 3 Manganese 129 Mastoidectomy 39 Matter disorders 121 Mediastinal mass 70, 121 Mediastinal tumors, anterior 170 Mediastinum 170 posterior 170f Meningioma 187 Meningitis 148, 149 chronic 149 Meniscal tear 179 Mesenchymal chondrosarcoma 141 Mesenchymal tumors 75, 164 Mesenteric angiography 97 Mesenteric veins 168 Mesothelioma, pleural 171f Metabolic disorders 162 Metabolism, inborn errors of 73, 160 Metachromatic leukodystrophy 151, 152f Metal artifact 103 Metal hip replacements 121 Metallic artifact 103f

Metallic bodies 121 Metastases 68, 121 Metastatic disease 187 Metformin therapy 39 Methylcellulose 129 Migration anomalies 38 Miliary tuberculosis 69 Mitochondrial disorders 203 Monocrystalline iron oxide nanocompounds 14 Motion artifact 84, 100, 101f Mucinous cystadenoma 164f Multinodular goiter 39 Multiplanar reformations 82 Muscles 121 Mycobacteria, atypical 190 Mycobacterium aviumintracellulare 190 kansasii 190 tuberculosis 195 xenopi 190 Myeloma 121 multiple 146 Myelopathy 185f Myeloproliferative disorders 164 Myoinositol 203

N N-acetylaspartate 203 Nasopharynx, level of 133f Nausea 20 Necrosis 71f, 203 Neimann-Pick disease 164 Neoplasm 39 benign 38 malignant 38 staging of 121 Neoplastic extradural mass 187 Nerve normal median 183f sheath tumors 187 Neurilemmoma 141 Neurocysticercosis 66, 67f Neurodegenerative disease 38 Neuroendocrine dysfunction 38 Neurofibroma 141, 187 Neurofibrosarcoma 141, 187 Neurogenic tumors 71, 170, 170f Neurologic deficits, acute 38 Neurolysis 91 Neutrons 3 Nodular liver, small 168f Nonalcoholic fatty liver disease 162

Noncardiac vessels, CT angiography of 85 Nonionizing radiation 4, 17 Nonossifying fibroma 141 Non-uric acid renal stone 83f Nuclear magnetic resonance 202 medicine 3 regulatory commission 19t

O Obesity 162 Ocular neoplasms 38 Oligodendrocyte 154 Oligodendroglioma 154 Optic chiasma 155 Optic pathways 155 Oral computed tomography contrast, advantages of 13 Oral contrast media 13 Orbital neoplasms 38 Orbits computed tomography 38 Organs, abdominal 51 Osseous procedures 93 Osteoblastoma 141 Osteochondroma 142, 143f Osteoclastoma 145 Osteoid osteoma 141, 142 Osteomyelitis 192f, 197f, 198f acute 192, 192f chronic 192 Osteoporosis 121 Osteosarcoma 141, 146 Otomastoid inflammatory disease acute 39 chronic 39

P Paget’s disease, atypical 141 Paget’s sarcoma 141 Pain 39 Palpable masses, evaluation of 38 Pancreas 45, 74, 75f, 162, 164f computed tomography 46t normal 163f Pancreatic ductal carcinoma 75 Pancreatic mass 54 Pancreatic neoplasms 75 Pancreatic pseudocyst 74 Pancreatic tumors 163 Pancreatitis 162 acute 49, 54, 74, 162, 165 chronic 162, 163, 163f

226  Textbook of Radiology for CT and MRI Technicians with MCQs Paraganglioma 71 Paramagnetic contrast agents 14 Paranasal sinuses computed tomography 38 Parenteral nutrition, total 161 Parieto-occipital region 151f Parosteal osteosarcoma 141 Parotid disorders 121 Pars interarticularis 185f Parvovirus 150 Pediatric brain 121 Pelvic computed tomography 38 Pelvis 48, 51, 113f Penumbra sign 193f Pericallosal hyperintensity 150f Pericardium 172 Peripheral angiogram 96f Peripheral circulatory failure 12 Peripheral nerve sheath tumor 71 Perisplenic collaterals 168 Peritoneal carcinomatosis 71 Periventricular hyperintensity 150f, 154f Personnel shielding 21, 22 Phosphate, triple 76 Phosphocreatine 203 Photomultiplier tubes 83 Photon detection 83 emission computed tomography, single 37 starvation 100, 102 Pilocytic astrocytoma 154f, 155 Pitch 33 Pituitary fossa lesions 121 Plasmacytoma 142 Pleomorphic xanthoastrocytoma 154f, 155 Pleural diseases, malignant 171 Pluripotential stem cells 164 Polycystic disease 158 Polycystic kidney disease, adult dominant 76 Polycystic liver disease 158 Polyethylene glycol 129 Porcelain gallbladder 167 Portal hypertension 160, 168f causes of 167 Portal vein 167 dilated 168 extrinsic compression of 167 invasion of 160 thrombosis 167 Portal venous phase 74f

Positron emission tomography 3, 37, 83, 84, 202, 205f scan 82 Pressure injection 41t basic physics of 40 Pressure injector components of 40 system 40, 41f Prevertebral abscess, small 195f Proptosis 38 Prostate cancer 188f Proton density weighting 118 Pulmonary angiography 97 Pulmonary tuberculosis, postprimary stage of 69, 69f Pyelonephritis, acute 53 Pyogenic arthritis, extra-articular spread of 190f Pyogenic infections 192, 197 Pyogenic meningitis, acute 148

R Radiation 17, 162 beta 3 biological effects of 19, 19f hazards 17 protection 17, 20, 22 actions 20 optimization of 20 safety officer 17 sources of 17 therapy 38, 39 treatment planning 38, 39 total dose of 18 Radiculopathy 121 Radioactive waste 17 Radiofrequency, low-frequency 17 Radiography, digital 5 Radiology basics of 3 modalities 3 Reaction, anaphylactic 11 Rectal computed tomography contrast 13 Rectal contrast 49, 57 Recurrent multifocal osteomyelitis, chronic 197f Renal abscess 53 angiography 97 artery stenosis 54 calculus, right 76f carcinoma 121 cell carcinoma 76, 77

computed tomography 46t failure, end stage 76 hematuria 40 infection 53 mass 53 stone 40, 53 water 49 ureteropelvic junction 54 Respiratory motion artifacts 86 Retroperitoneal hemorrhage 51 Ring artifact 100, 101f

S Salivary 121 Scan duration, shorter 82 Scan method 51-53, 55 Schistosoma japonicum 167 Schistosoma mansoni 167 Schistosomiasis 167 Schwannoma 187 Sclerosis, multiple 121, 150 Seizures 38, 121 Sensorineural hearing loss 39 Sepsis 43 Septic arthritis 193 Shock, anaphylactic 11 Shoulder 112f, 126 joint 175 Shunted hydrocephalus 38 Silicosis 69 acute 69 chronic 69 Sinonasal neoplasm 38 Sinus 39 computed tomography 47, 47t Skeletal interventions 91 Soft neck tissue computed tomography 38 Soft tissue 38 contrast 118 injury 187 Solitary bone cyst 142 Spin echo sequences advantages of 116 disadvantages of 116 Spinal cord astrocytoma 188 Spinal ependymoma 188, 188f Spinal meningioma 187f Spinal tuberculosis 196f Spine 113f, 121 computed tomography 47, 47t degenerative diseases of 185 infections of 195

 Index 227 tuberculosis of 195f, 196f upper dorsal 195f Spleen 164 Splenorenal collaterals 168 Spondylolisthesis 185 Spondylosis 185 Staphylococcus aureus 193, 197 Stoller and Colleagues grading 179 Stroke, time lapse appearance of 66t Sturge-Weber syndrome 121 Subarachnoid hemorrhage 65, 66f, 152 space 153f Subchondral bone attrition 182, 182f Subchondral cyst-like lesions 182 Subclavian angiography 96 Subdural hematoma 39, 65, 65f hemorrhage 152 Subependymal giant cell astrocytoma 155, 155f Subpleural bands 70f Subpleural septal thickening 70f Supraspinatus tear 176f complete full thickness 175, 176f Swelling 39 Sympathetic ganglia tumor 71 Syncope 38 Synovial chondromatosis 142 Synovial enhancement 193f joint effusion 193f Synovioma 142 Synovitis 182 stage of 190, 191 Synovium 121 Syringeless pressure injectors 43

T Taenia solium 66 Tau inversion recovery, short 116

Tears of supraspinatus, partial thickness 177f partial thickness 175, 177f small 128 Temporal bone 40, 47 computed tomography 39 Teratoma 170 Thermoluminescent dosimeter 23, 23f Thoracic procedures 93 Thoracic spine 124, 125, 186, 198f schwannoma 187f Thoracoabdominal aorta 97 Thoracolumbar junction 187 Thorax 51, 68 axial section of 60f Thymoma 70, 170 Thyroid 121 cancer 39 disease 170 ophthalmopathy 40 orbitopathy 38 scan 3 Tissue characterization 82 damage 96 Toxicity 11 Toxins 161 Toxoplasma gondii 150 Transitional cell carcinoma 77 of bladder 77 Trauma 38, 39, 51, 82, 164, 186 Traumatic bone bruise 121 Triphasic liver study 46t Tube arcing 100, 104 Tuberculoma 203 Tuberculosis 68, 190, 195, 196f Tuberculous arthritis 191f Tumor 91, 121, 187 ablation 93 angiogenesis 14 benign 121 malignant 121, 203



originate 164 staging 121 surgical treatment of 38

U Ulcer, nonhealing 96f Ultrasonography, types of 7 Ureteropelvic junction 54 Ureterovesical junction 53 Uric acid 76 Urinary bladder 77 tract calculus 76 Urolithiasis 76

V Vascular malformations 38 Vascular occlusive disease 38 Venography 14 Venous drainage of brain 138f hematogenous 197 Ventricle, lateral 155 Vertebral body involvement, multifocal dorsal 196f lesions, multiple 196f Viscera, abdominal 62f Vomiting 19, 20

W Whole body irradiation 19 Wilson disease 160 Wrist 113f joint 183

X X-ray 3, 4 tube 4f, 31 shielding 21