Radiology at a Glance E-Book

Rajat Chowdhury

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: At a Glance
• Sprache: Englisch

Seitenzahl: 283

Veröffentlichungsjahr: 2017

Beschreibung

Radiology at a Glance

The market-leading at a Glance series is popular among healthcare students, and newly qualified practitioners for its concise and simple approach and excellent illustrations.

Each bite-sized chapter is covered in a double-page spread with clear, easy-to-follow diagrams, supported by succinct explanatory text.

Covering a wide range of topics, books in the at a Glance series are ideal as introductory texts for teaching, learning and revision, and are useful throughout university and beyond.

Everything you need to know about Radiology… at a Glance!

Addressing the basic concepts of radiological physics and radiation protection, together with a structured approach to image interpretation, Radiology at a Glance is the perfect guide for medical students, junior doctors and radiologists.

Covering the radiology of plain films, fluoroscopy, CT, MRI, intervention, nuclear medicine and mammography, this edition has been fully updated to reflect advances in the field and now contains new spreads on cardiac, breast and bowel imaging, as well as further information on interventional radiology.

Radiology at a Glance:

• Assumes no prior knowledge of radiology
• Addresses both theory and clinical practice through theoretical and case-based chapters
• Provides structured help in assessing which radiological procedures are most appropriate for specific clinical problems
• Includes increased image clarity

Supported by ‘classic cases’ chapters in each section, and presented in a clear and concise format, Radiology at a Glance is easily accessible whether on the ward or as a quick revision guide.

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Radiology at a Glance

Second Edition

Rajat Chowdhury

MA (Oxon), BM BCh, MRCS, FRCR, FBIR Consultant Musculoskeletal Radiologist Oxford University Hospitals, UK

Iain D. C. Wilson

MEng (Oxon), BMedSci, BM BS, MRCS, FRCR Consultant Interventional Radiologist Southampton General Hospital, UK

Christopher J. Rofe

BSc (Hons), MB BCh, MRCP, FRCR Consultant Radiologist Borders General Hospital, Melrose, UK

Graham Lloyd-Jones

BA, MB BS, MRCP, FRCR Consultant Radiologist Salisbury District Hospital, UK

This edition first published 2018 © 2018 by John Wiley & Sons Ltd.

Edition HistoryFirst edition published 2010 © 2010 by Blackwell Publishing Ltd.

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The right of Rajat Chowdhury, Iain D. C. Wilson, Christopher J. Rofe and Graham Lloyd-Jones to be identified as the authors of this work has been asserted in accordance with law.

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Library of Congress Cataloging-in-Publication Data

Names: Chowdhury, Rajat, author. | Wilson, Iain D. C. (Iain David Cooper),  1975- author. | Rofe, Christopher J. (Christopher James), 1977- author. |  Lloyd-Jones, Graham, author.

Title: Radiology at a glance / by Rajat Chowdhury, Iain D.C. Wilson,  Christopher J. Rofe, Graham Lloyd-Jones.

Description: Second edition. | Hoboken, NJ : Wiley, 2017. | Series: At a  glance series | Preceded by Radiology at a glance / Rajat Chowdhury ...  [et al.]. 2010. | Includes index. |

Identifiers: LCCN 2017017189 (print) | LCCN 2017018823 (ebook) | ISBN  9781118914793 (pdf) | ISBN 9781118914786 (epub) | ISBN 9781118914779 (pbk.)

Subjects: | MESH: Diagnostic Imaging | Handbooks

Classification: LCC RC78.7.D53 (ebook) | LCC RC78.7.D53 (print) | NLM WN 39 |  DDC 616.07/54–dc23

LC record available at https://lccn.loc.gov/2017017189

Cover image: © arnitorfason/Gettyimages

CONTENTS

Contributors

Foreword

Preface

Abbreviations

Terminology

About the companion website

Part 1: Radiology physics

1: Plain X-ray imaging

Plain X-ray physics

The X-ray machine (tube)

Applying physics to practice

Image quality

Contrast

2: Fluoroscopy

Principles of fluoroscopy

The fluoroscopy machine

Applying physics to practice

Contrast fluoroscopy

Applications of fluoroscopy

3: Ultrasound

Ultrasound physics

The ultrasound scanner

Applications of ultrasound

Contrast ultrasound

4: Computed tomography

Computed tomography physics

Hounsfield units (HU)

The CT scanner

Applications of CT

Contrast agents

5: Magnetic resonance imaging

Magnetic resonance physics

Sequences

The MR scanner

Applications of MR

Contrast agents

Part 2: Radiology principles

6: Radiation protection and contrast agent precautions

Radiation exposure

Radiation protection

Radiation legislation

Iodinated contrast agent precautions

Contrast-induced nephropathy

MR contrast agent precautions

7: Making a radiology referral

Optimising the referral request

The radiology referral request

Notes

8: Which investigation?: classic cases

Trauma scenarios

Cardiovascular and respiratory scenarios

Head and neurological scenarios

Gastrointestinal scenarios

ENT scenarios

Musculoskeletal scenarios

Cancer scenarios

Genitourinary and gynaecological scenarios

Notes

Part 3: Plain X-ray imaging

9: Chest X-ray checklist and approach

Chest X-ray referral checklist (see Chapter 7)

Approach to CXR interpretation

10: Chest X-ray anatomy

Chest anatomy seen on PA CXR

Important anatomical landmarks and structures on the normal CXR

11: Chest X-ray classic cases I

Consolidation

Atelectasis

COPD

Lung/pulmonary fibrosis

12: Chest X-ray classic cases II

Cardiomegaly

Pulmonary oedema

Pleural effusion

Prosthetic heart valves

Pleural plaques

13: Chest X-ray classic cases III

Pneumothorax

Haemothorax

Lobar collapse

Tubes, lines and prostheses

14: Chest X-ray classic cases IV

Lung cancer

Mediastinal lymph node enlargement

Tuberculosis

Coin and cavitating lesions

Thoracic aortic aneurysm

15: Abdominal X-ray checklist and approach

Abdominal X-ray referral checklist (see Chapter 7)

Approach to AXR interpretation

16: Abdominal X-ray anatomy

Abdominal anatomy seen on AXR

Important anatomical landmarks and structures on AXR

17: Abdominal X-ray classic cases I

Bowel obstruction

Volvulus

Bowel perforation

18: Abdominal X-ray classic cases II

Inflammatory bowel disease

Calculi

Foreign body

Pneumobilia

19: Extremity X-ray checklist and approach

Extremity X-ray referral checklist (see Chapter 7)

Approach to extremity X-ray interpretation

20: Extremity X-ray anatomy I: upper limb

Upper limb anatomy seen on X-ray

21: Extremity X-ray anatomy II: pelvis and lower limb

Pelvis and lower limb anatomy seen on X-ray

22: Upper limb X-ray classic cases I: shoulder and elbow

Shoulder dislocation

Pathological fractures

Clavicle fracture

Acromioclavicular joint separation

Radial head fractures

Supracondylar fractures

23: Upper limb X-ray classic cases II: forearm, wrist and hand

Distal radius and ulna wrist fractures

Radius and ulna fractures

Carpal injuries

Osteoarthritis of the hand

Rheumatoid arthritis of the hand

Metacarpal fractures

24: Hip and pelvis X-ray classic cases

Neck of femur fracture

Pelvic ring fracture

Osteoarthritis of the hip

Paget’s disease

Paediatric hip lesions

25: Lower limb X-ray classic cases: knee, ankle and foot

Tibial plateau fractures

Lipohaemarthrosis

Osteoarthritis of the knee

Ankle fractures

Calcaneal fractures

Lisfranc fracture

Gout of the great toe

Calcium pyrophosphate dehydrate

Stress fractures

26: Face X-ray anatomy and classic cases

Face anatomy seen on X-ray

Approach to facial X-ray interpretation

Part 4: Fluoroscopic imaging

27: Fluoroscopy checklist and approach

Fluoroscopy referral checklist

Approach to interpreting fluoroscopic contrast studies

28: Fluoroscopy classic cases

Oesophageal lesions

Small bowel lesions

Part 5: Ultrasound imaging

29: Ultrasound checklist and approach

US referral checklist

Approach to US interpretation

30: Ultrasound classic cases

Liver lesions

Gall bladder lesions

Pancreatic lesions

Kidney lesions

Pleural effusion

Neck lumps

Scrotal lumps

Appendicitis

Part 6: Computed tomography imaging

31: Computed tomography checklist and approach

CT referral checklist

Approach to CT interpretation

32: Chest computed tomography anatomy

Chest anatomy seen on CT

Lungs and airways

33: Chest computed tomography classic cases I

Pneumonia

Pleural effusion

Bronchiectasis

Pneumothorax

COPD

Pulmonary fibrosis

34: Chest computed tomography classic cases II

Lung cancer

Mediastinal lymph node enlargement

Mesothelioma

Aortic dissection

Pulmonary embolism

35: Abdominal computed tomography anatomy

Abdominal anatomy seen on CT

36: Abdominal computed tomography classic cases I

Bowel pathology

Liver lesions

Ascites

Intra-abdominal abscess

37: Abdominal computed tomography classic cases II

Pancreatic lesions

Splenic lesions

Kidney and adrenal gland lesions

Abdominal aortic aneurysm

38: Head computed tomography anatomy

Extracranial structures

Cranium

Intracranial structures

39: Head computed tomography classic cases

Intracranial haemorrhage

Cerebral infarction

Intracranial tumours

Part 7: Specialised imaging and magnetic resonance imaging

40: Intravenous urography and computed tomography of kidneys, ureters and bladder

Urinary tract calculi

IVU

CT KUB

41: Computed tomography colonography

Colorectal cancer

National Health Service Bowel Cancer Screening Programme in England (NHS BCSP)

CT Colonography

42: Computed tomography and magnetic resonance angiography

CT angiography

MR angiography

Common applications of CTA and MRA

43: Magnetic resonance imaging checklist and approach

MRI referral checklist (see Chapter 7)

Approach to MRI interpretation

44: Head magnetic resonance imaging and classic cases

MRI of the head

Intracranial haemorrhage

Cerebral infarction and diffusion-weighted MRI

Intracranial tumours

45: Cervical spine imaging anatomy and approach

Plain X-ray imaging of the C-spine

CT imaging of the C-spine

MRI of the C-spine

46: Cervical spine imaging classic cases

Spondylolisthesis

C-spine degenerative disease/osteoarthritis

Odontoid peg fracture

Hangman’s fracture

Jefferson fracture

Teardrop fracture

47: Spine magnetic resonance imaging classic cases

Intervertebral disc herniation

Nerve root compression (radiculopathy)

Spinal cord and cauda equina compression

Spinal tumours

Ankylosing spondylitis

48: Cardiac computed tomography and classic cases

Coronary Artery Disease

Other applications of cardiac CT

49: Cardiac magnetic resonance imaging and classic cases

Coronary artery disease and myocardial infarction

Cardiomyopathy

50: Breast imaging

Breast cancer

National Health Service Breast Screening Programme (NHS BSP), England, UK

Mammography

Breast imaging in symptomatic patients

Classification of breast lesions

Breast MRI

Screening in high-risk patients

Part 8: Interventional radiology

51: Principles of interventional radiology

Fundamentals of interventional radiology

IR checklist

52: Interventional radiology classic cases

Vascular intervention

Nonvascular intervention

53: Interventional oncology classic cases

Liver intervention

Kidney intervention

Other intervention

Part 9: Nuclear medicine

54: Principles of nuclear medicine

Fundamentals of nuclear medicine

Hazards and precautions

55: Nuclear medicine classic cases

Ventilation/perfusion (V/Q) scanning

Bone scan

PET

Single photon emission computed tomography (SPECT)

Gated cardiac blood-pool imaging

Renal imaging

Index

EULA

Guide

Cover

Table of Contents

Preface

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Contributors

Madhuchanda Bhattacharyya

MA (Cantab), MBBS, MRCP, FRCR Consultant Breast Radiologist Oxford Breast Imaging Centre Oxford University Hospitals, UK

Dipanjali Mondal

BSc, MBBS, FRCR Consultant Radiologist Oxford University Hospitals, UK

Foreword

‘Radiology at a Glance’ – it won’t take most readers very long to realise that radiological images, like those in this book, deserve more than just a glance – in the old adage, ‘a picture is worth a thousand words’. Over the past 120 years since the discovery of X-rays, medical imaging has assumed an ever more central role in patient management. A familiarity with modern medical imaging techniques is an essential prerequisite for the practice of almost all branches of medicine. The past 40 years in particular have been dubbed the Golden Age of Radiology with the arrival on a regular basis of new techniques and modalities depicting human anatomy and disease processes in previously unthinkable detail. Ultrasound, computed tomography (CT), magnetic resonance imaging (MRI) and most recently positron emission tomography (PET) have all helped to shed light on structures and processes within the living human body which previously could only be imagined. The growth of interventional radiology has allowed the replacement of complex surgical procedures with minimally invasive techniques, often avoiding the need for anaesthesia and even hospital admission.

The authors of this excellent book, Rajat Chowdhury, Iain Wilson, Christopher Rofe and Graham Lloyd-Jones, have revised and expanded the bank of images displayed in this second edition to provide an even more comprehensive overview whilst retaining the clarity of presentation which characterised the first edition. New sections have been included on breast imaging, cardiac MRI and CT, CT colonography, and interventional oncology, representing some of the new frontiers in radiological practice. Further chapters on interventional radiology have also been added as well as new opportunities for self-assessment in the form of OSCE.

Medical students, junior doctors and healthcare practitioners from a wide range of backgrounds will find material here relevant to their learning and their daily practice and my hope is that it will fire their enthusiasm for medical imaging. The story of radiology does not end with the exquisite images of the beating heart which you will find in this volume. Functional imaging is with us already and new modalities are coming along in the near future which will enable us to move from imaging of gross anatomy to imaging at the cellular and molecular level and will support the key role that radiology plays in the era of personalised medicine.

Dr Giles Maskell

President of The Royal College of Radiologists (2013–2016)

Preface

Following the success of the first edition of Radiology at a Glance, we have implemented the feedback, updated and expanded the book, and maintained the classic at a Glance style to help teach the basics of radiology in a simple and clear fashion. We develop the reader from radiological anatomy through to classic pathological conditions that regularly appear in medical school exams. ‘Classic cases’ are found in separate chapters allowing easy access for doctors on the wards. The companion website now includes practice material for exam preparation.

We have written this book not only with medical students and junior doctors in mind, but trust that it will be a useful aid to students of radiography, nursing and physiotherapy, as well as other health professionals. We therefore hope it will be a valuable tool in gaining an understanding of the essentials of clinical radiology.

We would like to express our gratitude to all our colleagues and teachers for their inspiration, meticulous teaching and expert guidance. We extend warm thanks to Dr Giles Maskell for giving the second edition his prestigious seal of approval. We would also like to thank our publishers for all their enthusiasm and support in developing the renewed concept for the second edition. We would like to dedicate this book to our families who continue to support us along the at a Glance journey, and finally, we thank all our readers for taking the time to read this book, and in return we hope you feel it was time well spent.

Rajat Chowdhury Iain D. C. Wilson Christopher J. Rofe Graham Lloyd-Jones

Abbreviations

#

fracture

AAA

abdominal aortic aneurysm

ACL

anterior cruciate ligament

ADC

apparent diffusion coefficient

AIIS

anterior inferior iliac spine

ALARA

as low as reasonably achievable

AP

anterior to posterior

APTT

activated partial thromboplastin time

ARDS

acute respiratory distress syndrome

ARSAC

Administration of Radioactive Substances Advisory Committee

ASD

atrial septal defect

ASIS

anterior superior iliac spine

ATLS

Advanced Trauma Life Support

AVN

avascular necrosis

AXR

abdominal X-ray

Ba

barium

CAD

coronary artery disease

CAMG

coronary artery bypass grafting

CBD

common bile duct

CC

craniocaudal

CIN

contrast-induced nephropathy

COPD

chronic obstructive pulmonary disease

CPPD

calcium pyrophosphate dehydrate

CR

computed radiography

CSF

cerebrospinal fluid

C-spine

cervical spine

CT

computed tomography

CTA

computed tomographic angiography

CTCA

computed tomographic coronary angiography

CTKUB

computed tomography of kidneys, ureters and bladder

CTPA

computed tomographic pulmonary angiography

CTSI

computed tomography severity index

CXR

chest X-ray

DCS

ductal carcinoma in situ

DDH

developmental dysplasia of the hip

DEXA

dual energy X-ray absorptiometry

DIC

disseminated intravascular coagulation

DIPJ

distal interphalangeal joint

DMSA

dimercaptosuccinic acid

DOB

date of birth

DP

dorsal to plantar

DR

digital radiography

DRUJ

distal radioulnar joint

DTPA

diethylene triamine pentaacetic acid

DVT

deep vein thrombosis

DWI

diffusion-weighted (magnetic resonance) imaging

Echo

echocardiography

EDH

extradural haemorrhage/haematoma

EDV

end diastolic volume

EF

ejection fraction

eGFR

estimated glomerular filtration rate

EndoUS

endoultrasound

ERCP

endoscopic retrograde cholangiopancreatography

ESV

end systolic volume

EVAR

endovascular aneurysm repair

FB

foreign body

FDG

fluorodeoxyglucose

FEV

1

forced expiratory volume in 1st second

FLAIR

fluid attenuated inversion recovery

FNAC

fine-needle aspiration cytology

FOB

faecal occult blood

FVC

forced vital capacity

GI

gastrointestinal

GORD

gastro-oesophageal reflux disease

HIV

human immunodeficiency virus

HOC

hypertrophic obstructive cardiomyopathy

HRCT

high resolution computed tomography

HSE

Health and Safety Executive

IBD

inflammatory bowel disease

ICD

implantable cardioverter defibrillator

ICH

intracerebral haemorrhage

ICP

intracranial pressure

ID

identification details

INR

international normalised ratio

IR

interventional radiology

IR(ME)R 2000

Ionising Radiation (Medical Exposure) Regulations 2000

IRR99

Ionising Radiation Regulations 1999

IV

intravenous

IVC

inferior vena cava

IVU

intravenous urography

KUB

kidneys, ureters, bladder

LBO

large bowel obstruction

LLL

left lower lobe

LOS

lower oesophageal sphincter

LRTI

lower respiratory tract infection

LUL

left upper lobe

LUQ

left upper quadrant

LV

left ventricle

LVF

left ventricular failure

MAA

macroaggregated albumin

MAG3

mercaptoacetyl triglycine

MARS

Medicines (Administration of Radioactive Substances) Regulations

MCPJ

metacarpophalangeal joint

MDP

methylene diphosphonate

MEN

multiple endocrine neoplasia

MLO

mediolateral oblique

MR(I)

magnetic resonance (imaging)

MRA

magnetic resonance angiography

MRCP

magnetic resonance cholangiopancreatography

MTPJ

metatarsophalangeal joint

MUGA

multi-gated acquisition

NBM

nil by mouth

Neuro

neurological

NGT

nasogastric tube

NHS BSCP

NHS Bowel Cancer Screening Programme

NHS BSP

NHS Breast Screening Programme

NM

nuclear medicine

NOFF

neck of femur fracture

NSAID

non-steroidal anti-inflammatory drug

NSF

nephrogenic systemic fibrosis

N-STEMI

non-ST elevation myocardial infarction

OGD

oesophagogastroduodenoscopy

OM

occipitomental view

OPG

orthopantomogram

OSCE

Objective Structured Clinical Examination

PA

posterior to anterior

PACS

picture archiving and communications system

PCA

percutaneous coronary angioplasty

PCI

percutaneous coronary intervention

PCL

posterior cruciate ligament

PCNL

percutaneous nephrolithotomy

PCS

pelvicalyceal system

PD

proton density

PE

pulmonary embolus

PET

positron emission tomography

PET-CT

combined positron emission tomography with computed tomography

PICC

peripherally inserted central catheter

PIPJ

proximal interphalangeal joint

PT

prothrombin time

PTC

percutaneous transhepatic cholangiography

PUD

peptic ulcer disease

RA

right atrium

RCR

Royal College of Radiologists

RF

radiofrequency

RFA

radiofrequency ablation

RLL

right lower lobe

(R)ML

(right) middle lobe

RUL

right upper lobe

RUQ

right upper quadrant

RV

right ventricle

RWMA

Regional myocardial wall motion

SAH

subarachnoid haemorrhage

SBO

small bowel obstruction

SDH

subdural haemorrhage/haematoma

SIJ

sacroiliac joint

SOL

space occupying lesion

SPECT

single photon emission computed tomography

STEMI

ST elevation myocardial infarction

STIR

short tau inversion recovery

SUFE

slipped upper femoral epiphysis

SV

stroke volume

SVC

superior vena cava

TACE

transcatheter arterial chemoembolisation

TARE

transcatheter arterial radioembolisation

TB

tuberculosis

Tc-99m

metastable technetium-99

TFCC

triangulofibrocartilage complex

TIA

transient ischaemic attack

TIPS

transjugular intrahepatic portosystemic shunt

TNM

tumour, nodes, metastases

UC

ulcerative colitis

UGI

upper gastrointestinal

US

ultrasound

V/Q

ventilation-perfusion

Terminology

Attenuation

Gradual loss in intensity of beams and waves including X-rays and ultrasound waves. May also be used synonymously with ‘density’ to describe appearances on CT imaging (areas of high attenuation are bright whereas areas of low attenuation are dark).

Density

Used synonymously with ‘attenuation’ to describe appearances on CT imaging (areas of high density are bright whereas areas of low density are dark).

Echogenicity

Used synonymously with ‘reflectivity’ to describe appearances on ultrasound imaging (hyperechoic areas are bright whereas hypoechoic areas are dark).

Hotspot/coldspot

Used to describe the uptake of radiopharamaceutical agents by tissues in nuclear medicine imaging (increased uptake results in a hotspot whereas reduced uptake results in a coldspot).

PACS

The ‘picture archiving and communication systems’ are computer networks that store, retrieve, distribute and present medical images electronically. This permits images to be viewed and manipulated digitally on screen with remote and instant access by multiple users simultaneously and has therefore almost replaced the use of hard-copy films in the UK.

Reflectivity

Used synonymously with ‘echogenicity’ to describe appearances on ultrasound imaging (hyperreflective areas are bright whereas hyporeflective areas are dark).

Signal

Used to describe appearances on MRI (areas of high signal are bright whereas areas of low signal are dark).

About the companion website

Don’t forget to visit the companion website for this book:

http://www.ataglanceseries.com/chowdhury/radiology/

There you will find valuable material designed to enhance your learning, including:

Radiology OSCE, case studies and questions

Flash cards

Figures from the book in PowerPoint format, to download

Part 1Radiology physics

Chapters

Plain X-ray imaging

Fluoroscopy

Ultrasound

Computed tomography

Magnetic resonance imaging

1Plain X-ray imaging

Plain X-ray physics

On 8 November 1895, the German physicist Wilhelm Conrad Röentgen discovered the X-ray, a form of electromagnetic radiation which travels in straight lines at approximately the speed of light. X-rays therefore share the same properties as other forms of electromagnetic radiation and demonstrate characteristics of both waves and particles. X-rays are produced by interactions between accelerated electrons and atoms. When an accelerated electron collides with an atom two outcomes are possible:

An accelerated electron displaces an electron from within a shell of the atom. The vacant position left in the shell is filled by an electron from a higher level shell, which results in the release of X-ray photons of uniform energy. This is known as characteristic radiation.

Accelerated electrons passing near the nucleus of the atom may be deviated from their original course by nuclear forces and thereby transfer some energy into X-ray photons of varying energies. This is known as Bremsstrahlung radiation.

The resultant beam of X-ray photons (X-rays) interacts with the body in a number of ways:

Absorption – this prevents the X-rays reaching the X-ray detector plate. Absorption contributes to patient dose and therefore increases the risk of potential harm to the patient.

Scatter – scattering of X-rays is the commonest source of radiation exposure for radiological staff and patients. It also reduces the sharpness of the image.

Transmitted – transmitted X-rays penetrate completely through the body and contribute to the image obtained by causing a uniform blackening of the image.

Attenuation – an X-ray image is composed of transmitted X-rays (black) and X-rays which are attenuated to varying degrees (white to grey). Attenuation can be thought of as a sum of absorption and scatter and is determined by the thickness and density of a structure. In the chest, structures such as the lungs are relatively thick but contain air, making them low in density. The lungs therefore transmit X-rays easily and appear black on the X-ray image. Conversely, bones are not thick but are very dense and therefore appear white. Attenuation can be controlled by varying the power or ‘hardness’ of the X-ray beam.

The X-ray machine (tube)

Most modern radiographic machines use electron guns to generate a stream of high energy electrons, which is achieved by heating a filament. The high energy electrons are accelerated towards a target anode. The electrons hit the anode, thereby generating X-rays as described above. This process is very inefficient with 99% of this energy transferred into heat at 60 kV. The dissipation of heat is therefore a key design feature of these machines to sustain their use and maintain their longevity. The material for the target anode is selected depending on the chosen task and the energy of the X-ray beam can be modified by filtration to produce beams of uniform energy.

Most modern radiology departments now employ digital imaging techniques and there are two principal methods in everyday use: computed radiography (CR) and digital radiography (DR). CR uses an exposure plate to create a latent image, which is read by a laser stimulating luminescence, before being read by a digital detector. DR systems convert the X-ray image into visible light, which is then captured by a photo-voltage sensor that converts the light into electricity, and thus a digital image. The final digital images are stored in medical imaging formats and displayed on computer terminals.

Applying physics to practice

If the subject to be imaged is placed further from the detector, the image created will be magnified. This is based on the principle that X-ray beams travel in diverging straight lines.

Scatter from the patient and other objects degrades the resolution. This will cause the image to be blurred.

Beams of lower energy are absorbed more than beams of higher energy. This affects the difference in clarity between the soft tissue detail and artefact.

Image quality

The clarity of the image can be expressed as ‘unsharpness’. This can be classified into:

Inherent unsharpness – this is caused by the structures involved not having sharp, well-defined edges.

Movement unsharpness – this can be reduced by using short exposures, as with light photography.

Photographic unsharpness – this is dependent on the quality and type of imaging equipment and the method of capturing the image.

Newer digital imaging systems now allow the postprocessing of data to enhance various aspects of the image.

Contrast

The contrast of an image is dependent on the variation of beam attenuation within the subject. There are five principal densities that can be seen on a plain radiographic image.

Plain X-ray densities

Black

Dark grey

Light grey

White

Bright white

Air/gas

Fat

Soft tissue/fluid

Bone and calcified structures

Metal

The contrast may be increased by lowering the energy of the X-ray beam. However, this has negative impact on image quality and increases the dose of radiation.

Contrast agents are often used to enhance anatomical detail. A desirable contrast agent is one that has high photoelectric absorption at the energy of the X-ray beam. The contrast agents most commonly used in plain X-ray imaging are barium, gastrografin (water soluble) and iodinated compounds. Precautions in the use of iodinated contrast agents are discussed in Chapter 6.

Advantages and disadvantages of plain X-ray imaging

Advantages

Disadvantages

• Inexpensive

• Radiation exposure

• Fast

• Imaging three-dimensional structures in a two-dimensional format

• Simple

• Low tissue contrast

• Readily available

• Overlapping anatomy

• No dynamic or functional information

2Fluoroscopy

Principles of fluoroscopy

Fluoroscopy allows dynamic real-time imaging of the patient, which can provide information regarding the movement of anatomical structures or devices within the patient. Fluoroscopy is based on X-ray imaging and the physical principles are similar to the plain X-ray imaging chain from X-ray beam generation to image display (see Chapter 1). However, the procedure is performed using a specifically designed X-ray machine and uses low dose real-time acquisition techniques and hardware.

The fluoroscopy machine

There are two main types of fluoroscopy machines:

Continuous low energy X-ray production systems.

Pulsed X-ray production systems – these are used more commonly in practice due to the lower radiation dose given to the patient (and to radiological staff).

Fluoroscopy machines are designed specifically to manage the heat generated from the repeated exposure in fluoroscopic imaging. They also use lower beam energies and exposures compared with plain X-ray imaging techniques and thus image intensifiers are employed to enhance the image. These convert the X-rays to electrons to amplify the signal several thousand-fold and then convert the electron beams again into visible light. This light image is then transmitted onto a screen.

Static images, which are similar to plain X-ray images, can be acquired. These provide increased contrast and spatial resolution compared to standard fluoroscopy images, but at the cost of increased patient dose.

Applying physics to practice

When using image intensifiers, several factors must be

considered:

Patient dose

– this is partially dependent on the distance from the patient to the X-ray tube. It is important to maintain the tube-to-screen distance as large as possible and to place the patient as close as possible to the screen. This will help to keep the doses as low as reasonably achievable (ALARA) (see Chapter 6). The dose is also influenced by the total exposure time and the number of spot images acquired.

Image magnification

– the image magnification by the hardware increases the entrance dose to the surface of the patient.

Coning

– this reduces the area exposed to radiation therefore reducing the patient dose, but also improves image quality.

Contrast fluoroscopy

For the majority of fluoroscopic imaging, contrast agent enhancement is used. Fluoroscopy gives the ability to make real-time adjustments to the patient’s position and image orientation, which often reveals invaluable information to help differentiate the diagnosis. This is most evident when using contrast-enhanced imaging of the bowel.

Applications of fluoroscopy

Contrast gastrointestinal imaging

Videofluoroscopy

– this is a study which takes multiple images per second to look at real-time anatomical and functional properties during the oropharyngeal phase of swallowing.

Contrast swallow

– this is a study looking at real-time images of the anatomical and functional properties of the oesophageal phase of swallowing. This can also give information regarding the oropharyngeal phase but it is less detailed than videofluoroscopy.

Barium meal

– this provides a method of imaging the stomach and proximal small bowel. However, it has been largely superseded by endoscopy.

Small bowel meal

– this is a study that provides anatomical and functional information regarding the small bowel. The patient swallows a bolus of contrast agent and then timed interval images are taken as it passes through the small bowel until it reaches the terminal ileum. At this point, focused images are taken to identify diseases of the terminal ileum, e.g. Crohn’s disease.

Small bowel enema

– this study is similar to a small bowel meal but contrast agent is pumped through a nasojejunal tube. The bolus is then followed more carefully with real-time images through the entire small bowel. To achieve double contrast, methylcellulose is also given via the nasojejunal tube.

Double contrast barium enema