A Comprehensive Guide to Radiographic Sciences and Technology E-Book

Euclid Seeram

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 436

Veröffentlichungsjahr: 2021

Beschreibung

A Comprehensive Guide to Radiographic Sciences and Technology is a concise review of radiographic physics and imaging, perfect for students preparing for certification examinations such as the American Registry for Radiologic Technologists (ARRT). Aligned with the core radiographic science components of the current American Society of Radiologic Technologists (ASRT) curriculum, this up-to-date resource covers topics including radiation production and characteristics, imaging equipment, digital image acquisition and display, radiation protection, basic principles of computed tomography, and quality control. The guide begins with an overview of the radiographic sciences and technology, followed by detailed descriptions of the major components of digital radiographic imaging systems. Subsequent sections discuss the essential aspects of diagnostic radiography and computed tomography, including basic physics, imaging modalities, digital image processing, quality control, imaging informatics, and basic concepts of radiobiology and radiation protection. Throughout the book, concise chapters summarise the critical knowledge required for effective and efficient imaging of the patient while emphasising the important, yet commonly misunderstood, relationship between radiation dose and image quality. Written by an internationally recognised expert in the field, this invaluable reference and guide: * Provides easy access to basic physics, techniques, equipment, and safety guidelines for radiographic imaging * Reflects the educational requirements of the American Society of Radiologic Technologists (ASRT), the Canadian Association of Medical Radiation Technologists (CAMRT), the College of Radiographers(CoR), and other radiography societies and associations worldwide * Offers a range of pedagogical tools such as chapter outlines, key term definitions, bulleted lists, practical examples, and links to current references and additional resources * Includes charts, diagrams, photographs, and x-ray images A Comprehensive Guide to Radiographic Sciences and Technology is required reading for students in programs using ionizing radiation, those preparing for the ARRT and other global radiography certification exams, and practising technologists wanting to refresh their knowledge.

Leseprobe

A Comprehensive Guide to Radiographic Sciences and Technology

Euclid Seeram, PhD, MSc, BSc, FCAMRT

Full Member – Health Physics Society

ACADEMIC APPOINTMENTSAdjunct Associate Professor; Medical Imaging and Radiation Sciences; Monash University, Melbourne, Australia | Adjunct Professor; Faculty of Science; Charles Sturt University, Bathurst, Australia | Adjunct Professor; Medical Radiation Sciences, Faculty of Health; University of Canberra, Canberra, Australia

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Library of Congress Cataloging‐in‐Publication Data

Names: Seeram, Euclid, author.Title: A comprehensive guide to radiographic sciences and technology / Euclid Seeram.Description: First edition. | Hoboken, NJ : Wiley‐Blackwell, 2021. | Includes bibliographical references and index.Identifiers: LCCN 2020050277 (print) | LCCN 2020050278 (ebook) | ISBN 9781119581840 (paperback) | ISBN 9781119581833 (adobe pdf) | ISBN 9781119581857 (epub)Subjects: MESH: Radiography–methods | Radiography–instrumentation | Image Processing, Computer‐Assisted | Technology, Radiologic | Radiation ProtectionClassification: LCC RC78.2 (print) | LCC RC78.2 (ebook) | NLM WN 200 | DDC 616.07/572–dc23LC record available at https://lccn.loc.gov/2020050277LC ebook record available at https://lccn.loc.gov/2020050278

Cover Design: WileyCover Image: © Cybrain/iStock/Getty Images

Dedication

This book is dedicated with love to my Family; my lovely wife, Trish; our son David and daughter-in-law Priscilla; and our two very smart, cute, and witty granddaughters, Claire and Charlotte

Foreword

Dr Euclid Seeram is a recognized educator in the field of radiographic sciences, including computed tomography (CT) physics and instrumentation for radiologic technologists/radiographers. He has published over 22 textbooks on various topics related to these two subjects. His textbooks can be found in universities and colleges around the world that offer medical imaging and radiographic science programs. He has a very well‐developed approach in all his textbooks that allows the reader to understand complex topics.

Dr Seeram has decades of experience in the teaching radiographic sciences and CT. Euclid is also a highly regarded researcher in this field, gaining a PhD in digital radiography and radiation dose management strategies. He has continued to work and research in this area. Euclid is also a highly sought‐after speaker and provides highly engaging talks and presentations on radiographic sciences and CT. The impact of Euclid's texts, journal articles, and presentations has had on radiologic technologists/radiographers, other related individuals, and medical physicists in their understanding of radiographic sciences and CT, cannot be understated.

The development of the technologies that underpin radiological science continues to grow rapidly and at an increasing rate. Students need to understand these technologies and the implications of these technologies in clinical practice. The approach undertaken by Dr Seeram in this text, A Comprehensive Guide to Radiographic Sciences and Technology, is to provide readers with clearly defined chapters on several related topics. The chapters and sections of this book are logically structured so the readers/learners can progress their understanding. Of growing importance in radiographic sciences, and often misunderstood, is the understanding of the radiation dose/image quality relationship of digital radiography. This area has a strong focus in this textbook. Furthermore, the knowledge gained from studying the subject matter covered in this book will benefit technologists/radiographers in clinical practice in order to provide tangible benefits to their patients.

I have been fortunate to know Dr Seeram for over 20 years, initially as his PhD supervisor, and now as a coresearcher, colleague, and friend/mate. Euclid continues to amaze me on his dedication and passion to educate radiologic technologists/radiographers and his drive to continue writing. Euclid must be commended for his continued efforts in making radiographic sciences, and CT knowledge easy to understand by students and practitioners.

Dr Robert Davidson, PhD, MAppSc (MI), BBus, FASMIRTProfessor of Medical Imaging, Faculty of Health, University of Canberra, ACT, Australia

Preface

Radiographic sciences and technology include a wide range of topics essential for radiography/radiological technology curriculum offered by educational institutions (colleges, universities, and institutes of technology) around the world. Additionally, radiography/radiological technology/medical imaging professional organizations for radiographer/technologist education and training, such as, for example, the American Association of Radiologic Technologists (ASRT) and the Canadian Association of Medical Radiation Technologists (CAMRT) offer curriculum guidelines for educational institutions to use as guiding principles for core clinical competencies. More details of related activities are highlighted in Chapter 1.

This book includes 13 chapters organized into 6 sections as follows:

Section 1

:

Chapters 1

and

2

Section 2

: Basic Radiographic Sciences and Technology

Section 3

: Computed Tomography: Basic Physics and Technology

Section 4

: Continuous Quality Improvement

Section 5

: Picture Archiving and Communications Systems (PACS) and Imaging Informatics

Section 6

: Radiation Protection

PURPOSE

The purpose of this book, A Comprehensive Guide to Radiographic Sciences and Technology, is to provide an essential and practical guide for students and technologists engaged in the study and practice of radiography/radiological technology. One of its primary goals is to provide a resource that is brief, clear, and a concise coverage of the subject in preparation for final examinations as well as professional certification examinations. This book is not a textbook as such, and it is not intended to replace the vast resources on radiographic sciences and technology. Rather, it provides a précis of the extensive coverage of radiographic sciences and technical system components for students and technologists.

CORE OBJECTIVES

On the successful completion of the chapters in this book, the reader will be able to:

Outline the core subject matter content of radiographic imaging modalities.

Identify and describe briefly the major technical components of digital radiographic imaging systems.

Outline the basic physics necessary for understanding essential concepts and principles for x‐ray generation, production, x‐ray emission, x‐ray interaction with matter, and radiation attenuation in the production of diagnostic images in clinical practice.

Describe the major components of the x‐ray generator and x‐ray tube including heat capacity and heat dissipation and x‐ray beam filtration and collimation.

Explain the core principles of digital image processing, including the characteristics of the digital image and common image processing operations applied in practice.

Identify and explain the fundamental physics principles and technology of the following digital imaging modalities: computed radiography (CR), flat‐panel digital radiography (FPDR), and digital fluoroscopy.

Identify image quality metrics and explain each of them with a focus on how dose is linked to image quality.

Describe the basic physics of computed tomography (CT) and explain the major technological considerations of multislice CT (MSCT), including image post processing, image quality metrics, and radiation protection considerations in CT.

Identify the essential elements of quality control (QC), including the principles of a repeat analysis, and describe the performance criteria for common QC tests for radiography, fluoroscopy, and CT.

Describe the core technical components of PACS, and explain briefly the general subject matter comprising imaging informatics, including artificial intelligence and its subsets: machine learning and deep learning.

Outline the major principles of radiobiology, with a specific focus on relevant physical processes, dose–response models, stochastic and deterministic effects, as well as radiation effects on the conceptus.

Explain the technical factors affecting the dose in radiography, fluoroscopy, and CT.

Identify and discuss the major components of radiation protection including radiation protection philosophy of the International Commission on Radiological Protection (ICRP), radiation quantities and units, personnel dosimetry, optimization of radiation protection, and the current state of gonadal shielding.

USE OF THESE OBJECTIVES AND CONTENT

These objectives and content covered in this book may be used in the following subjects covered in standard radiography/radiological technology programs:

Physics of Radiography

Digital Radiography Equipment Including Digital Fluoroscopy

Image Quality

PACS and Imaging Informatics

Quality Control in Radiography and Fluoroscopy

Computed Tomography Physics and Instrumentation for Entry to Practice

Radiobiology for Diagnostic Radiography

Radiation Protection in Diagnostic Radiography

Chapter 1 introduces the nature and scope of radiographic sciences and technology and sets the general framework for the remaining chapters. Whereas Chapter 2 presents a description of the major technical components of digital radiographic imaging modalities, such as computed radiography (CR), FPDR, digital fluoroscopy, and digital mammography, Chapter 3 describes the essential physics of radiography, including principles for x‐ray generation, production, x‐ray emission, x‐ray interaction with matter, and radiation attenuation in the production of diagnostic images in clinical practice. Chapter 4 examines the major technical components of the x‐ray generator and x‐ray tube, describing core technologies such as the x‐ray circuit, x‐ray generators, the structure and function of the x‐ray tube, heat capacity and dissipation, as well as the nature of x‐ray beam filtration and collimation. Chapter 5 reviews the fundamental elements of digital image processing beginning with a definition, followed by a review of image formation and representation, processing operations, characteristics of digital images, and gray‐scale processing, most notably the nature of windowing. Chapters 6 and 7 address the principles and technology of digital radiographic imaging modalities, identified in Chapter 2, and image quality and dose, respectively. Chapter 8 covers the essential technical aspects of CT, at a depth needed for entry‐to‐practice, including the basic physics and technology of CT. Specifically, the major technical system components of MSCT are described. Furthermore, image processing, image quality, and radiation dose and radiation protection are described. Chapter 9 provides a discussion of quality control and focusses on the performance criteria/tolerance limits for common QC tests for radiography, fluoroscopy, and CT tests that are in the domain of the technologist. Finally, the chapter reviews the elements of repeat image analysis. The nature of imaging informatics including major topics as picture archiving and communication systems (PACS), and specific imaging topics such as enterprise imaging, cloud computing, Big Data, and artificial intelligence, and its subsets, machine learning and deep learning, are reviewed in Chapter 10. Finally, Section 6 covers topics in radiation protection. In particular, while Chapter 11 provides a discussion of basic concepts of radiobiology, Chapter 12 deals with the technical dose factors in radiography, fluoroscopy, and CT. Finally, the book concludes with Chapter 13, which addresses the essential principles of radiation protection, focusing on topics such as a rationale for radiation protection, objectives of radiation protection, radiation protection philosophy of the International Commission on Radiological Protection (ICRP), radiation quantities and units, personnel dosimetry, optimization of radiation protection, and the current state of gonadal shielding.

Enjoy the pages that follow and remember – your patients will benefit from your wisdom.

Euclid Seeram, PhD., MSc., BSc., FCAMRTBritish Columbia, Canada

Acknowledgments

It is always a pleasure to acknowledge the contributions of experts in the field of radiographic sciences including radiologic physics, equipment, image quality, quality control, radiobiology and radiation protection from whom I have learned a great deal that allows me to write this book.

First, I am indeed grateful to all those who have dedicated their energies in providing several comprehensive volumes on radiologic physics and instrumentation for the radiologic community. I would like to acknowledge the notable medical physicist, Dr. Stewart Bushong ScD, FAAPM, FACR and experimental radiobiologist, Dr. Elizabeth Travis, PhD. I have learned a great deal on radiologic science from the works of Dr. Bushong, a professor of radiologic science in the Department of Radiology, Baylor College of Medicine, Houston, TX. In addition, I have gained further insight into the nature, scope, and depth of radiobiology and particularly its significance in radiology, from Dr. Travis, a researcher in the Department of Experimental Radiotherapy, University of Texas, MD Anderson Cancer Center, Houston, TX.

Secondly, I am grateful to physicist, Dr. Hans Swan, PhD and digital radiography expert, Dr. Rob Davidson, PhD, who served as my primary supervisors for my PhD dissertation entitled Optimization of the Exposure Indicator of a Computed Radiography Imaging System as a Radiation Dose Management Strategy. Furthermore, Dr. Stewart Bushong served as an external examiner for my PhD dissertation. Additionally, two other notable medical physicists from whom I have learned my digital radiography imaging physics and technology are Dr. Charles Willis, PhD (University of Texas; MD Anderson Cancer Center‐Retired) and Dr. Anthony Seibert, PhD (University of California at Davis). Dr. Seibert's notable textbook on The Essential Physics of Medical Imaging has educated me in the core principles of medical imaging physics. Thanks to you all.

I must acknowledge all others, such as the authors whose papers I have cited and referenced in this book, thank you for your significant contributions to radiographic sciences knowledge base. Additionally, I would like to express my sincere thanks to Dr. Perry Sprawls, PhD, FACR, FAAPM, FIOMP, Distinguished Emeritus Professor, Emory University, Director, Sprawls Educational Foundation, http://www.sprawls.org, Co‐Director, College on Medical Physics, ICTP, Trieste, Italy, and Co‐Editor, Medical Physics International, http://www.mpijournal.org/.

Dr. Sprawls has always supported my writing and I appreciate his free resources on the World Wide Web (www) from which students, technologists, and educators alike can benefit. I must also mention Dr. Anthony Wolbarst, PhD, Medical Physics Department, University of Kentucky (Retired).

Another individual to whom I owe a good deal of thanks is Valentina Al Hamouche, MRT(R), MSc, who is the CEO/Founder VCA Education Solutions for Health Professionals http://www.VCAeducation.ca. Valentina has provided me with opportunities to provide radiographic sciences and CT physics and Instrumentation in‐house lectures and webinars to further educate technologists and students across Canada and internationally. Thanks Valentina.

I must acknowledge James Watson, Commissioning Editor, Wiley, Oxford, UK, who understood and evaluated the need for this book. Additionally, I am grateful to Anupama Sreekanth, former project editor and current managing editor Anne Hunt at Wiley, for the advice and support you both provided to me during the writing stage of this book. Furthermore, I appreciate the work of Sandeep Kumar, Content Refinement Specialist at Wiley, who has done an excellent job in bringing this manuscript to fruition.

Finally, I am very grateful for the warm and wonderful support of my family: my lovely wife, Trish, a very wise and caring person; and my very smart son, David, a very special young man and the best Dad in the universe. Thank you both for your unending love, support, and encouragement.

Last, but not least, I want to express my gratitude to all the students in my radiographic sciences classes – your questions have provided me with a further insight into teaching this important subject. Thank you.

SECTION 1Introduction

1Radiographic sciences and technology: an overview

RADIOGRAPHIC IMAGING SYSTEMS: MAJOR MODALITIES AND COMPONENTS

RADIOGRAPHIC PHYSICS AND TECHNOLOGY

Essential physics of diagnostic imaging

Digital radiographic imaging modalities

Radiographic exposure technique

Image quality considerations

Computed tomography – physics and instrumentation

Quality control

Imaging informatics at a glance

RADIATION PROTECTION AND DOSE OPTIMIZATION

Radiobiology

Radiation protection in diagnostic radiography

Technical factors affecting dose in radiographic imaging

Radiation protection regulations

Optimization of radiation protection

Bibliography

Radiographic Science and Technology have evolved through the years, ever since the discovery and use of x‐rays in 1895. This evolution has resulted in the introduction of physical principles and technology with the major goal of improving the care and management of the patient. Furthermore, a significant benefit of these innovations is focused on reducing the radiation dose to the patient without compromising image quality. Radiographic sciences deal with the physics of various diagnostic imaging modalities (radiography, fluoroscopy, mammography, and computed tomography [CT]) and include x‐ray generation, x‐ray production, x‐ray emission, and x‐ray interaction with tissues. Furthermore, radiographic sciences also address radiation risks and radiation protection. Radiographic technology, on the other hand, addresses the equipment components and how they function to produce diagnostic images, image quality characteristics, and quality control (QC) aspects of these imaging modalities.

The workhorse of radiology has been film‐screen radiography which is now obsolete and has been replaced globally with digital imaging. The scope of digital imaging is extremely wide and now involves a basic understanding of computer sciences, to explain how the new digital imaging modalities work. These modalities include computed radiography (CR), flat‐panel digital radiography (FPDR), digital fluoroscopy (DF), digital mammography (DM), digital tomosynthesis, and CT. In addition, the digital imaging environment now demands that operators understand what has been referred to as “imaging informatics,” an area of study that involves picture archiving and communication systems (PACS), enterprise imaging, Big Data, machine learning (ML), deep learning (DL), and artificial intelligence (AI).

With the above in mind, various professional organizations such as the American Society of Radiologic Technologists (ASRT), the Canadian Association of Medical Radiation Technologists (CAMRT), and other professional medical imaging organizations throughout the world have prescribed curricula for diagnostic imaging programs which provide guiding, principles that assist academic program leaders in designing foundational learning outcomes that are intended to meet the professional standards, and more importantly meet the entry requirements for clinical practice. Institutions offering educational programs in diagnostic imaging should be then able to raise the level of these foundational learning outcomes and content to meet the requirements of degree programs, including graduate degree programs in diagnostic imaging.

A good example of the above is offered by the ASRT curriculum content which is organized around the following subject matter [1]: Introduction to Radiologic Science and Health Care; Ethics and Law in the Radiologic Sciences; Human Anatomy and Physiology; Pharmacology and Venipuncture; Imaging Equipment; Radiation Production and Characteristics; Principles of Exposure and Image Production; Digital Image Acquisition and Display; Image Analysis; Radiation Biology; Radiation Protection; Clinical Practice; Patient Care in Radiologic Sciences; Radiographic Procedures; Radiographic Pathology; Additional Modalities and Radiation Therapy; Basic Principles of Computed Tomography and Sectional Anatomy. Similar content is characteristic of other curricula offered by other medical imaging professional organizations around the world.

Keeping the above ideas in mind, this book will address content that are considered radiographic sciences and technology. Specifically, the chapters included present a summary of the critical knowledge base needed for effective and efficient imaging of the patient, and wise use of the technical factors that play a significant role in optimization of the dose to the patient without compromising the image quality necessary for diagnostic interpretation. Furthermore, the summaries of the technical elements of radiographic sciences and technology will assist the student in preparing to write certification examinations. As such, the major and significant principles and concepts will be reviewed in three sections as follows:

Section 1: Radiographic imaging systems: major modalities and components

Section 2: Radiographic physics and technology

Section 3: Radiation protection and dose optimization

RADIOGRAPHIC IMAGING SYSTEMS: MAJOR MODALITIES AND COMPONENTS

In this book, the following radiographic imaging systems will be reviewed. These include x‐ray imaging modalities such as digital radiography (DR) which includes CR and FPDR, DF, DM, digital radiographic and breast tomosynthesis, and CT. Furthermore, these systems include imaging informatics which has become commonplace since radiology and more importantly hospitals are now all operating in the digital environment; that is, all data acquired from the patient are now in digital form and are stored and communicated using digital technologies. Informatics topics of importance include that nature and scope of PACS, enterprise imaging, cloud computing, Big Data, and the more recent of computer applications in medical imaging: AI. More details of these major technologies and how they work will be presented in Chapter 6 on Digital Imaging Modalities and Chapter 10 on Imaging Informatics.

RADIOGRAPHIC PHYSICS AND TECHNOLOGY

Radiographic physics and technology subject matter include basic physics concepts, and more specifically the physics of diagnostic imaging; technical aspects of the modalities; radiographic exposure technique; image quality, quality assurance (QA), and QC; CT physical principles; imaging informatics; radiobiology and radiation protection.

Essential physics of diagnostic imaging

The physics of diagnostic imaging is an important and vital topic that explains the nature of how these imaging modalities work to produce diagnostic images of the patient. Understanding the fundamental physics will provide the user with the tools not only needed to produce optimum image quality but more importantly to protect the patient from unnecessary radiation. As such, it is now a common characteristic of imaging departments to optimize radiation dose and work within the International Commission on Radiological Protection (ICRP) philosophy of as low as reasonably achievable (ALARA) to reduce the dose to the patient but not compromise the diagnostic quality of the images used to make a diagnosis of the patient's medical condition.

In this book, the topics in physics that will emphasize the imaging modalities are the nature of radiation, x‐ray generation, x‐ray production, x‐ray emission, x‐ray attenuation, and x‐ray interaction with matter. Furthermore, other physics topics of significance are radiation quantities and their associated units and measurement concepts. These topics and more fall in the domain of Health Physics. Three radiation quantities that are important to radiation protection of the patient are exposure, absorbed dose, and effective dose (ED). The units associated with each of these include coulombs per kilogram (C/kg), Grays (Gy), and Sieverts (Sv), respectively. In order to measure radiation, it must first be detected.

Digital radiographic imaging modalities

As listed earlier in this chapter, these modalities include CR, FPDR or DR as it is sometimes referred to, DF, DM, digital radiographic tomosynthesis (DRT), digital breast tomosynthesis (DBT), and last but not least CT. Additionally, since all of the above‐mentioned modalities include image processing using computers, the concepts of Digital Image Processing will be reviewed since it has become an essential tool for technologists, radiologists, and medical physicists working in a digital radiology department.

These imaging modalities include specific physics concepts that must be understood for optimum results. For example, CR is based on the use of photostimulable phosphors (PSP) which are based on the physical principle of photostimulable luminescence (PSL). An example of one such phosphor is barium fluoro halide (BaFX) where the halide (X) can be chlorine (Cl), bromine (Br), iodine (I), or a mixture of them. When the PSP imaging plate (IP) is exposed to x‐rays, electrons are moved from the ground state (valence band) to a higher energy level (conducting band) and are trapped there until the PSP plate is exposed to a laser light and subsequently the electrons in the higher energy state return to their ground state, thus emitting a bluish‐purple light referred to as PSL.

The detectors used in FPDR are based on semiconductor physics. Examples of two such common detectors used in DR are indirect digital detectors which use amorphous silicon photoconductor coupled to an x‐ray scintillator (cesium iodide for example) and direct digital detectors which use amorphous selenium photoconductor. While the former detector converts x‐rays to light which falls upon the silicon photoconductor to produce electrical signals, the latter detector converts x‐rays directly into electrical signals. The other digital imaging modality detectors are based on photoconductor physics.

The imaging modalities listed above convert radiation attenuated by the patient and falling on the digital detector to digital data. This is necessary since computers are used to process these data through popular digital image processing operations. These operations have become commonplace and must be fully understood for effective use in clinical practice. One such tool is the concept of windowing, where the image brightness and contrast can be changed by the operator to suit the viewing needs of the human interpreter. Furthermore, other digital image processing tools that are vital in DBT and CT image reconstruction algorithms. These algorithms have evolved from the filtered back projection (FBP) algorithm to more complex algorithms such as iterative reconstruction (IR) algorithms. These algorithms play an important role in building up an image from data collected through 360° around the patient in CT, for example. Today, IR algorithms are now used by all CT vendors.

Radiographic exposure technique

Radiographic exposure technique refers to the use of exposure factors coupled with other elements on the x‐ray control panel, selected by the technologist to produce diagnostic images. Exposure factors include the kilovoltage (kV), the milliamperes (mA), and exposure time (s) and the selection of the appropriate source‐to‐image receptor distance (SID). Furthermore, the proper positioning of the patient and image receptor, tube alignment with the image receptor, use of appropriate filtration and collimation, and patient instructions, are all the other elements that play an important role during the radiographic examination.

Image quality considerations

Image quality is a significant goal of radiographic imaging modalities. The attenuated radiation data from the patient are used to create images that are used for diagnostic interpretation by a human observer. There are at least five important descriptors of digital image quality and these include spatial resolution, contrast resolution, noise, detective quantum efficiency (DQE), and image artifacts. While spatial resolution addresses the sharpness of images, and is related to the size of the pixels (picture elements) in an image, contrast resolution or density resolution deals with the ability of the imaging system to demonstrate differences in tissue contra, and is linked to the bit depth, that is the range of gray levels per pixel. Noise, on the other hand, depends on the number of x‐ray photons used to create the image. While fewer photons (low exposure technique factors) will result in more noise (grainy appearance), more photons (higher exposure technique factors) will create a better image (less noisy image), but at the expense of dose. Another digital image quality descriptor is the DQE, which is a measure of the efficiency and fidelity with which the detector can convert an input exposure into a useful output image. Finally, digital images are not free of artifacts. These are features seen on the image that are not present in the patient, and can pose challenges for the human observer in detecting fact from artifact.

Computed tomography – physics and instrumentation

This section will present a broad overview of the essential elements of the Physics and Instrumentation of Computed Tomography. One of the major advantages of CT is that it provides improved contrast resolution compared to radiography and for this reason, it has proven to be worthy of further developments in imaging soft tissues of the human body. It is important to note, however, that magnetic resonance imaging (MRI) has superior contrast resolution compared to all other imaging modalities, such as radiography, nuclear medicine, and diagnostic medical sonography.

CT is a sectional imaging technique that produces direct cross‐sectional digital images referred to as transverse axial images which has been referred to as planar sections that are perpendicular to the long axis of the patient. The word “computed” implies that a computer is used to process and reconstruct x‐ray transmission data collected from the patient. The CT scanner has evolved from single‐slice CT scanners (SSCT) to multi‐slice CT scanners (MSCT). State‐of‐the‐art CT scanners are now MSCT scanners capable of a wide range of applications. The increasing use is that CT in clinical practice has led to increasing doses to the patient and a well‐documented fact is that CT delivered the highest collective dose in the United States compared to other medical imaging modalities.

Two individuals shared the Nobel Prize in Medicine and Physiology in 1979 for their development of the CT scanner. These include Godfrey Newbold Hounsfield in the United Kingdom (UK) who invented the first clinically useful scanner, and Allan Cormack, a physicist at Tufts University in Massachusetts.

CT is a multidisciplinary technology and has its roots in physics, mathematics, engineering, and computer science. The CT process consists of at least three major system components that are used to produce the CT image; the data acquisition system; the computer system; and the image display, storage, and communication systems.

Data acquisition means that radiation attenuation data are collected from the patient during the scanning. In this respect, an x‐ray tube coupled to special electronic detectors rotate around the patient to collect and measure attenuation readings as the x‐ray beam passes through the patient.

The attenuation is according to Beer–Lambert's law:

where I is the transmitted x‐ray beam intensity, Io is the original x‐ray beam intensity, e represents Euler's constant, μ is the linear attenuation coefficient, and Δx is the finite thickness of the section. In CT, the system calculates all μs for all structures seen on the image. Special detectors and detector electronics are used to calculate the attenuation data and convert them into integers (0, a positive number, or a negative number) referred to as CT numbers using an image reconstruction algorithm to build up the image in numerical format. The CT numbers (numerical image format) are converted into a gray‐scale image for display on a monitor for the observer to interpret.

The CT numbers are calculated using the following relationship:

where K represents a scaling factor. In general, K is equal to 1000. When Hounsfield invented the scanner, K was equal to 500.

The technology aspects of CT are complex and are responsible for using the attenuation values collected around the patient for 360° to build up an image of the internal anatomy of the patient, and displays such image for interpretation by radiologists. The technology addressing the collection of these values includes the x‐ray tube which is coupled to special electronic detectors and detector electronics. Another major technology component in CT is the computer system which captures the raw data from the detectors and uses sophisticated image reconstruction algorithms for creating the image from the raw data.

Present‐day CT scanners are MSCT scanners. One characteristic feature of MSCT is the two‐dimensional detector array, compared to a one‐dimensional detector array of SSCT. This means that there will be additional specific technical factors that affect the dose in CT. One such notable factor is the pitch (P), which is defined by the International Electrotechnical Commission (IEC) as the distance the table travels per rotation (D) divided by the total collimation (W). This can be expressed algebraically as:

The increasing use of CT has led to widespread concerns about high patient radiation doses from CT examinations relative to other radiography examinations. The distribution of the dose to the patient in CT is significantly different than the distribution of the dose in radiography. These differences require additional CT‐specific dose metrics. There are essential four CT‐specific dose metrics: the computed tomography dose index (CTDI), the dose length product (DLP), the size‐specific dose estimate (SSDE), and the ED. These and other elements of CT physical principles will be described further in Chapter 7.

Quality control

QC is an essential activity of all medical imaging departments and it is part of a QA program. QA deals with people and includes the administrative aspects of patient care and quality outcomes. QC addresses the technical aspects of equipment performance used to image patients. QA and QC programs have evolved into what is now referred to as Continuous Quality Improvement (CQI) which includes Total Quality Management (TQM). CQI was introduced by the Joint Committee on Accreditation of Healthcare organizations (JCAHO) to stress the importance that all employees play an active role in ensuring a quality product. The purpose of the procedures and techniques of CQI, QA, and QC is threefold: to ensure optimum image quality for the purpose of enhancing diagnosis, to optimize the radiation dose to patients and reduce the dose to personnel, and to reduce costs to the healthcare facility.

An effective QC program consists of at least three major steps, namely acceptance testing, routine performance, and error correction. While acceptance testing is the first major step in a QC program and it ensures that the equipment meets the specifications set by the manufacturers, routine performance involves performing the actual QC test on the equipment with varying degrees of frequencies (annually, semi‐annually, monthly, weekly, or daily). Error correction means that equipment not meeting the performance criteria or tolerance limit established for specific QC tests must be replaced or repaired to meet tolerance limits. These limits include both qualitative and quantitative criteria used to assess image quality. For example, the tolerance for collimation of the x‐ray beam should be ±2% of the SID.

QC for DR has evolved from simple to more complex tests and test tools to assure that the DR equipment is working properly to meet optimum image quality standards and fall within the ALARA philosophy in radiation protection. The American Association of Physicists in Medicine (AAPM) has recommended that several testing procedures for CR QC, using specific tools developed for CR QC. A few examples of these test procedures include physical inspection of IP, dark noise and uniformity, exposure indicator (EI) calibration, laser beam function, spatial accuracy, erasure thoroughness, aliasing/grid response, positioning and collimation errors, to mention a few.

QC is now an essential requirement of CT imaging and requires that users have a clear understanding of the various tests that play a significant role in dose‐image quality optimization.

Imaging informatics at a glance

Imaging Informatics is the current term used by the Society of Imaging Informatics in Medicine (SIIM) to replace the old term medical imaging informatics. SIIM notes that imaging informatics “is the study and application of processes of information and communications technology for the acquisition, manipulation, analysis, and distribution of image data.”