This page intentionally left blank S E C O N D E D I T I O N SUZANNE AMADOR KANE Haverford College Pennsylvania, USA Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business A TAYLOR & FRANCIS BOOK CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2009 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-13: 978-1-58488-943-4 (Softcover) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher can- not assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copy- right.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that pro- vides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Amador Kane, Suzanne. Introduction to physics in modern medicine / Suzanne Amador Kane. -- 2nd ed. p. cm. Includes bibliographical references and index. ISBN 978-1-58488-943-4 (pbk. : alk. paper) 1. Medical physics. I. Title. R895.A518 2009 610.1’53--dc22 2009011772 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com To my husband, Charlie This page intentionally left blank Contents Instructor’s preface x i Student preface xiii Preface to the second edition x v Acknowledgments xvii 1 Introduction and overview 1 Suggested reading 8 2 Telescopes for inner space: Fiber optics and endoscopes 1 1 2.1 Introduction 11 2.2 Optics: The science of light 15 2.2.1 How to see around corners 15 2.2.2 Reflecting and bending light 18 2.2.3 Why does light bend? The index of refraction 19 2.2.4 Optional: How lenses form images 23 2.2.5 Making pipes for light 26 2.3 Fiber optics applications in medicine: Endoscopes and laparoscopes 33 2.3.1 Different types of endoscopes and their typical construction 33 2.3.2 Some advantages and disadvantages 42 2.3.3 Laparoscopic gallbladder removals 43 2.4 New and future directions 44 2.4.1 Robotic surgery and virtual reality in the operating room 44 2.4.2 Telemedicine and military applications 46 2.4.3 Innovations on the horizon 48 Resources 49 Questions 50 Problems 50 Reflection and refraction 50 Total internal reflection and fiber optics 50 Advanced problems 53 vii viii Contents 3 Lasers in medicine: Healing with light 5 5 3.1 Introduction 55 3.2 What is a laser? 56 3.3 More on the science of light: Beyond the rainbow 59 3.4 How lasers work 63 3.5 How light interacts with body tissues 70 3.6 Laser beams and spatial coherence 72 3.7 Cooking with light: Photocoagulation 77 3.8 Trade-offs in photocoagulation: Power density and heat flow 78 3.9 Cutting with light: Photovaporization 80 3.10 More power: Pulsed lasers 81 3.11 Lasers and color 84 3.12 The atomic origins of absorption 87 3.13 How selective absorption is used in laser surgery 91 3.14 Lasers in dermatology 95 3.15 Laser surgery on the eye 97 3.16 New directions: Lasers in dentistry 101 3.17 Advantages and drawbacks of lasers for medicine 102 3.18 New directions: Photodynamic therapy—Killing tumors with light 103 3.19 New directions: Diffusive optical imaging 106 Suggested reading 108 Questions 109 Problems 110 4 Seeing with sound: Diagnostic ultrasound imaging 115 4.1 Introduction 115 4.2 Sound waves 118 4.3 What is ultrasound? 121 4.4 Ultrasound and energy 124 4.5 How echoes are formed 125 4.6 How to produce ultrasound 129 4.7 Images from echoes 132 4.8 Ultrasound scanner design 139 4.9 Ultrasound is absorbed by the body 143 4.10 Limitations of ultrasound: Image quality and artifacts 151 4.11 How safe is ultrasound imaging? 157 4.12 Obstetrical ultrasound imaging 161 4.13 Echocardiography: Ultrasound images of the heart 165 4.14 Origins of the Doppler effect 166 4.15 Using the Doppler effect to measure blood flow 171 4.16 Color flow images 173 Contents ix 4.17 Three-dimensional ultrasound 174 4.18 Portable ultrasound—Appropriate technology for the developing world 176 Suggested reading 178 Questions 180 Problems 181 Basic physics of sound waves 181 Echo ranging and echo intensity 181 Absorption of ultrasound 183 Sources of distortion 183 Doppler ultrasound 184 Another useful source of problems on ultrasound imaging 185 5 X-ray vision: Diagnostic X-rays and CT scans 187 5.1 Introduction 187 5.2 Diagnostic x-rays: The body’s x-ray shadow 190 5.3 Types of x-ray interactions with matter 191 5.4 Basic issues in x-ray image formation 198 5.5 Contrast media make soft tissues visible on an x-ray 206 5.6 How x-rays are generated 210 5.7 X-ray detectors 217 5.8 Mammography: X-ray screening for breast cancer 225 5.9 Digital radiography 231 5.10 Computed tomography (CT) 238 5.11 Application: Spotting brittle bones—Bone mineral scans for osteoporosis 249 Suggested reading 252 Questions 253 Problems 255 Interaction of x-rays with matter 255 Contrast, contrast media, and x-ray absorption 255 X-ray sources and detectors 256 6 Images from radioactivity: Radionuclide scans, SPECT, and PET 259 6.1 Introduction: Radioactivity and medicine 259 6.2 Nuclear physics basics 261 6.3 Radioactivity fades with time: The concept of half-lives 264 6.4 Gamma camera imaging 270 6.5 Emission tomography with radionuclides: SPECT and PET 278 6.6 Application: Emission computer tomography studies of the brain 290 6.7 Hybrid scanners 293