Nuclear Medicine Physics The Basics 6th Edition 2004 Lippincott Williams & Wilkins Philadelphia 530 Walnut Street, Philadelphia, PA 19106 USA 978-0-7817-4753-0 0-7817-4753-8 Acquisitions Editor: Lisa McAllister Developmental Editor: Kathryn Stadel Production Editor: Jeffrey Somers Manufacturing Manager: Colin Warnock Cover Designer: Karen Quigley Compositor: TechBooks Printer: Maple-Press © 2004 by LIPPINCOTT WILLIAMS & WILKINS 530 Walnut Street Philadelphia, PA 19106 USA LWW.com All rights reserved. This book is protected by copyright. No part of this book may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotations embodied in critical articles and reviews. Materials appearing in this book prepared by individuals as part of their official duties as U.S. government employees are not covered by the above-mentioned copyright. Printed in the USA Fifth Edition, 1998 Library of Congress Cataloging-in-Publication Data Chandra, Ramesh, 1938- Nuclear medicine physics: the basics/Ramesh Chandra.—6th ed. p. ; cm. Includes bibliographical references and index. ISBN 0-7817-4753-8 (pbk.) 1. Medical physics. 2. Nuclear medicine. 3. Radioisotopes. I. Title. [DNLM: 1. Health physics. 2. Nuclear medicine. 3. Radioisotopes. WN 110 C457n 2004] R895.C47 2004 616.07′575—dc22 2002043075 Care has been taken to confirm the accuracy of the information presented and to describe generally accepted practices. However, the authors, editors and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication. Application of this information in a particular situation remains the professional responsibility of the practitioner. The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new or infrequently employed drug. Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice. 10 9 8 7 6 5 4 3 2 1 iv Dedication To my wife, Mithilesh, my son, Anurag, and my daughter, Ritu v AUTHORS Ramesh Chandra PhD Professor Department of Radiology New York University Medical Center New York, New York vi Preface The purpose and the audience for this new edition of this book and the subject matter remains the same as in previous editions. I quote, “This book is primarily addressed to resident physicians in nuclear medicine as well as residents in radiology, pathology, and internal medicine who wish to acquire knowledge of nuclear medicine. Nuclear medicine technologists wishing to advance in their field should also find this book useful. I have tried to write in a simple and concise manner, including not only essential details but also many examples and problems taken from the routine practice of nuclear medicine. Basic principles and underlying concepts are explained. Mathematical equations or in some cases their derivations have been included only when it was felt their inclusion will help the reader and when it was essential for the proper development of the subject matter. However, the reader is warned that this is not an introductory book of physics, and, therefore, familiarity on his or her part with the elementary concepts of physics, such as units, energy, force, electricity, and light, is assumed by the author.” However, since the publication of earlier editions, PET has emerged from being a valuable research tool to being an important clinical tool in the diagnosis of a variety of diseases. As a result, PET is no longer limited to a few specialized laboratories, but has spread to most clinical nuclear departments. Therefore, I have now added new material to cover this area of nuclear medicine. In particular, the following additions have been made:  In Chapter 2, decay scheme of 18F, the most common radionuclide used in PET, has been added.  In Chapter 5, a section on the common radiopharmaceuticals for PET has been added.  In Chapter 8, a section on detectors used in PET devices has been added.  In Chapter 14, the section on PET instrument has been enlarged and sections on PET-CT and SPECT/CT have also been included.  In Chapter 16, aspects related to protection from PET radiopharmaceuticals are discussed. Other significant changes are:  Since there was a good response to the problems at the end of each chapter, these have been enlarged.  The number of figures has been increased and now for the first time the book includes pictures of the important instruments.  Chapter 15 has been augmented with a new section on Contrast/details curves and ROC. Again, I thank all the readers and teachers who wrote to me or emailed with their commendations and/or criticism, or who brought the errors to my attention. I would also like to thank Martha Helmers for all her help in vii preparation of figures. Last, but not the least, I thank the publisher and his staff for their help and cooperation in bringing my labor to fruition. Ramesh Chandra New York, New York viii Contents Authors Dedication Preface 1 - Basic Review 2 - Nuclides and Radioactive Processes 3 - Radioactivity: Law of Decay, Half-Life, and Statistics 4 - Production of Radionuclides 5 - Radiopharmaceuticals 6 - Interaction of High-Energy Radiation With Matter 7 - Radiation Dosimetry 8 - Detection of High-Energy Radiation 9 - In Vitro Radiation Detection 10 - In Vivo Radiation Detection: Basic Problems, Probes, and Rectilinear Scanners 11 - In Vivo Radiation Detection: Scintillation Camera 12 - Operational Characteristics and Quality Control of a Scintillation Camera 13 - Detectability or Final Contrast in an Image 14 - Emission Computed Tomography 15 - Biological Effects of Radiation and Risk Evaluation from Radiation Exposure 16 - Methods of Safe Handling of Radionuclides and Pertaining Rules and Regulations Appendix A Appendix B Appendix C Appendix D Appendix E Answers Suggestions for Further Reading Index 1 1 Basic Review From a physicist's point of view, nature consists mainly of matter and the forces governing the behavior of matter. This chapter reviews briefly some aspects of the atomic structure of matter that are essential for the understanding of subsequent subject matter. Matter, Elements, and Atoms All matter is composed of a limited number of elements (105 or so) that in turn are made of atoms. An atom is the smallest part of an element that retains all its chemical properties. In general, atoms are electrically neutral; that is, they do not show any electric charge. However, atoms are not indivisible as once was thought but are composed of three elementary particles: electrons, protons, and neutrons. An electron is a tiny particle that possesses a negative charge of 1.6022 × 10−19coulomb (unit of charge) and a mass of 9.109 × 10−31 kg. A proton is a particle with a positive charge equal in amount to that of an electron. A neutron does not have any electric charge and weighs slightly more than a proton. Protons and neutrons have masses of 1.6726 × 10−27 and 1.6749 × 10−27 kg, respectively; hence, they are about 2000 times heavier than an electron. Simplified Structure of an Atom An atom is generally neutral because it contains the same number of electrons and protons. The number of protons in an atom is also known as the atomic number Z. It specifies the position of that element in the periodic table and therefore specifies its chemical identity. The electrons, protons, and neutrons in an atom are arranged in a planetary structure in which the protons and neutrons (the sun) are located at the center and the electrons (planets) are revolving over the surface of spherical shells (or orbits) of different radii. The center in which the protons and neutrons are located is known as the nucleus and is similar to a packed sphere. The size of atoms of different elements varies greatly but is in the range of 1 to 2 × 10−10 m. The nucleus is really small in comparison to the atom (about 105 times smaller or 10−15m in size). The attractive coulomb (electrical) force between the positively charged nucleus (due to the protons) and the negatively charged electrons provides stability to the electrons revolving in the spherical shells. The first shell (having the smallest radius) is known as the K shell, the second shell as L, the third shell as M, and so on. There is a limit to the number of electrons that can occupy a given shell. The K shell can be occupied by a maximum of 2 electrons, the L shell by a maximum of 8 electrons, the M shell by a maximum of 18 electrons, and the N shell by a maximum of 32 electrons. However, the outermost shell in a given atom cannot be occupied by more than eight electrons. In a simple atom like hydrogen, there is only one electron that under normal circumstances occupies the K shell. In a complex atom like iodine, there are 53 electrons that are arranged in the K, L, M, N, and O orbits in numbers of 2, 8, 18, 18, and 7, respectively. The arrangement of electrons in various shells for hydrogen and three other typical atoms is shown in Fig. 1.1. This is a simplified description of the atomic structure that, in reality, is more complex as each shell is further divided into sub-shells. For our purpose, however, it is more than sufficient. 2 Fig. 1.1. Simplified atomic structure of four elements in their ground state. Molecules Molecules are formed by the combination of two or more atoms (e.g., a molecule of water, HO, is formed by the 2 combination of two hydrogen atoms and one oxygen atom). The combination of atoms is accomplished through the interaction of electrons (also known as valent electrons) in the outermost orbits of the atom. Valent electrons participate in the formation of the molecules in several ways—for example, in ionic binding, covalent binding, and hydrogen binding. In theory, most chemical reactions and chemical properties of atoms or molecules can be explained on the basis of the interaction of the valent electrons. Binding Energy, Ionization, and Excitation Each electron in a given shell is bound to the nucleus with a fixed amount of energy. Therefore, if one wishes to remove an electron from a particular shell to make it free and no longer associated with that atom, energy will have to be provided to the electron from outside the atom. The minimum amount of energy necessary to free an electron from an atom is known as the binding energy of the electron in that atom. The unit in which energy is measured on the atomic scale is known as an electron volt (eV), which is the energy acquired by an electron accelerated through 1 volt of potential difference. The electrons in the K shell are the most tightly bound electrons in an atom and therefore require the most energy to be removed from the atom. Electrons in the outermost shell, on the other hand, are the least tightly bound electrons and therefore require the least amount of energy for their removal from the atom. The binding energy of electrons in various shells increases rapidly with the atomic number Z. Table 1.1 lists the K- and L-shell average binding energies of electrons in the atoms of various elements.