MRI: A Conceptual Overview PDF
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MRI A Conceptual Overview Springer Science+Business Media, LLC Sunder S. Rajan M RI A Conceptual Overview With 117 Illustrations Sunder S. Rajan, Ph.D. Library of Congress Cataloging-in-Publication Data Rajan, Sunder S. MRI: a conceptual overview / Sunder S. Rajan. p. cm. Includes bibliographical references and index. ISBN 978-0-387-94911-6 ISBN 978-1-4612-1632-2 (eBook) DOI 10.1007/978-1-4612-1632-2 1. Magnetic resonance imaging. 2. Nuclear magnetic resonance. I. Title RC78.7.N83R35 1997 616.07'548—dc21 96-37408 Printed on acid-free paper. © 1998 Springer Science+Business Media New York Originally published by Springer-Verlag New York., Inc. in 1998 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher Springer Science+Business Media, LLC. except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. While the advice and information in this book are believed to be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Please carefully review the complete prescribing information for any drug product prior to patient administration. Sunder S. Rajan, Ph.D., holds a B.Sc. (Madras Christian College), an M.Sc. (IIT Kampor), and a Ph.D. (University of Chicago), all in Chemistry. He is currently employed by Bracco Diagnostics Inc. in Princeton, NJ, as an Associate Director, Clinical Research. Prior to that, he was employed in the Department of Radiol ogy at Georgetown University Medical Center in Washington, DC. Production coordinated by Chernow Editorial Services, Inc., and managed by Bill Imbornoni; manufacturing supervised by Rhea Talbert. Typeset by Best-set Typesetter Ltd., Hong Kong 9 8 7 6 5 4 3 2 1 ISBN 978-0-387-94911-6 To my parents, Kanaka and Seshadri, with gratitude and respect Thanks for your patience, Sunder Preface Over the course of just a few decades, magnetic resonance (MR) has evolved from an analytical tool to a premier imaging mod ality. The ability of MR to provide cross-sectional images, as well as chemical and physiological information, has attracted students from many disciplines. Because applied MR is multidisciplinary, it is generally taught in an informal setting rather than as structured course work. During my years of teach ing the subject, I felt the need for an appropriate text for students from diverse backgrounds. The materials now available are ei ther basic introductions for the lay person or detailed reference resources providing detailed coverage of one or more aspects of MRI. I wrote this book to supplement informal teaching with a text that will provide a detailed conceptual overview. This approach to presenting the concepts will be useful for graduate students in the physical, chemical, and biological sciences who are making the transition to MRI. In addition, medical residents, fellows, and experienced MRI technologists will benefit from this de scriptive approach to MRI, which is briefly summarized in the next paragraph. Chapter I, an introduction to the magnetic resonance phenom enon, is followed by principles of image formation in Chapter 2. The link between the theoretical concepts introduced in Chapter 2 to the actual operation of an MRI instrument is made in Chap ter 3. Chapter 4 describes the principles of image contrast, which plays a pivotal role in clinical MRI. Chapter 5, on contrast agents, introduces an exciting dimension of MRI that will continue to see progress in the coming decades. Chapter 6 provides clinical ex amples that will serve to inform the reader of the versatility and usefulness of clinical MRI. Chapters 7 and 8 introduce vascular imaging and spectroscopy. MRI is rapidly progressing, and new applications continue to emerge. One of the challenges in writing this text has been to keep abreast of the rapid expansion of applications and viii Preface methodology of MRI. If the book aids in providing a struc tured teaching tool for students of MRI despite the continuing progress in MRI technology, I will have accomplished my mission. SURNDER S. RAJAN Acknowledgments This text was initially conceived as an extracurricular project with my colleagues, Drs. Mark Carvlin and Denis LeBihan, at Georgetown University. Unfortunately, they left Georgetown just after this project began. Mark was kind enough to contribute to the chapter on "Contrast Agents" and Denis to Appendix on "K-space Formalism." I would like to thank them immensely for their support, without which I would not have embarked on this long journey. I would also like to thank my students, especially Kathleen Ward, and my friends at Georgetown, Drs. Susan Ascher, Chin-Shoou Lin, Richard Patt, Craig Platenberg, and David Thomasson, for their insights and assistance. Thanks are also due to Alicia Montgomery for her help with the transcription and to my father-in-law Warren Grinde who was kind enough to proof the manuscript. Last, but not least this text would have not reached completion had it not been for the constant encouragement and support of my wife, Ingrid Grinde. Contents Preface .......................................... vii Acknowledgments ................................ ix 1. Introduction to the Phenomenon of Nuclear Magnetic Resonance. . . . . . . . . . . . . . . . . . . . 1 2. Magnetic Field Gradient Pulses and Spatial Encoding of MR Signal ........................ 12 3. MRI Hardware System Components..... . . . ... . . 25 4. Image Contrasts and Pulse Sequences 40 5. Contrast Agents ............................... 66 6. Clinical Applications ..... . . . . . . . . . . . . . . . . . . . . . . 76 7. Flow Effects and MR Angiography. . . . . . . . . . . . . . . .. 100 8. Spectroscopy ................................. 130 Appendix. k-Space Formalism. . .. . . . . . .... . .. . . . . . 154 Index. . . .... ..... . . . ... . . .... . . . ... ... . .. .. ...... 161 1 Introduction to the Phenomenon of Nuclear Magnetic Resonance Historical Magnetic resonance imaging (MRI) has emerged as one of the most powerful diagnostic tools in the radiology clinic. The chief strengths of MRI are its ability to provide cross-sectional images of anatomical regions in any arbitrary plane and its excellent soft-tissue contrast. MRI has the ability to provide functional as well as anatomical information. The nuclear energy states of certain atoms interact with incident radio frequency photons in the presence of a static magnetic field. The radio frequency emis sion by tissue that follows the absorption of photons can be exploited to generate images. The phenomenon responsible for this, called the nuclear magnetic resonance (NMR) effect, was discovered almost simultaneously by Purcell and Bloch in 1946. It was recognized from the start that the nuclear magnetic reso nance effect could be used to probe the electronic structure of molecules. NMR has since emerged as an invaluable analytical tool for molecular structure determination. It was only in the early 1980s that the nuclear magnetic resonance effect was ex ploited for imaging. In this chapter we will lay a foundation for an understanding of MRI by examining the basis of the reso nance effect. The Resonance Effect Magnetic resonance is a phenomenon that has its origin in the magnetic properties of atomic particles such as electrons, pro tons, and neutrons, which form the building blocks of atoms and molecules. For reasons beyond the scope of this book, nuclei of
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