Imaging Techniques of the CNS of the Neonates PDF
Preview Imaging Techniques of the CNS of the Neonates
1. Haddad D. Christmann 1. Messer (Eds.) Imaging Techniques of the eNS of the Neonates With Contributions by D. I. Altmann, B. Brunot, G. M. Bydder, E. B. Cady, A. Calame, D. Christmann, A. Constantinesco, D. T. Delpy, C. L. Fawer, 1. Haddad, 1. Hennig, E. Martin, 1. Messer, 1. 1. Volpe, 1. S. Wyatt With 251 Figures Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Budapest JOSEPH HADDAD, M. D. Service de Medecine et Reanimation du Nouveau-Ne Centre Hospitalier Universitaire de Hautepierre ~ Strasbourg Avenue Moliere 67098 Strasbourg Cedex, France DOMINIQUE CHRISTMANN, M. D. Radiopediatrie ~ Service de Radiologie II Centre Hospitalier Universitaire de Hautepierre ~ Strasbourg Avenue Moliere 67098 Strasbourg Cedex, France JEAN MESSER, Prof. Service de Neonatologie Service de Medecine et Reanimation du Nouveau-Ne Centre Hospitalier Universitaire de Hautepierre ~ Strasbourg Avenue Moliere 67098 Strasbourg Cedex, France Library of Congress Cataloging-in-Publication Data. Imaging techniques of the CNS of the neonates / 1. Haddad, D. Christmann, 1. Messer (eds.). p. cm. Includes bibliographical referen ces and index. ISBN-13: 978-3-642-76490-5 e-ISBN-13: 978-3-642-76488-2 DOl: 10.1007/ 978-3-642-76488-2 1. Central nervous system-Imaging. 2. Infants (Newborn)-Diseases-Diagnosis. 3. Central Nervous System-Diseases-Diagnosis. I. Haddad, 1. (Joseph) II. Christmann, D. III. Messer, 1. RJ290.I42 1991 618.92'80754-dc20 91-20738 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplica tion of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its current version and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law. © Springer-Verlag Berlin Heidelberg 1991 Softcover reprint of the hardcover 1st edition 1991 The use of general descriptive names, registered names, trademarks, etc. in this publication does not irnply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Product liability: The publishers can give no guarantee for information about drug dosage and application thereof contained in this book. In every individual case the respective user must check its accuracy by consulting other pharmaceutical literature. Reproduction of the figures: Gustav Dreher GmbH, 0-7000 Stuttgart Typesetting: Konrad Triltsch, Graphischer Betrieb, Wiirzburg 21/3130-543210 - Printed on acid-free paper Preface There has been increasing interest in neonatal neurology, especially since imaging techniques were introduced in the neonatal ward. Looking at the natural history of imaging techniques, we can identify three main axes of its development. Logically, it was first essential to image the brain morphologically. For this purpose, computed tomography was initially used, followed by ultra sound. However, to improve the quality of the images, magnetic resonance imaging was introduced. Major features of ultrasound and magnetic reso nance imaging are their safety and lack of ionization. Morphological imaging techniques have proved to be insufficient to ex plain the mechanisms underlying CNS injuries. Thus, it was essential to develop functional techniques to assess cerebral hemodynamics and oxy genation. The use of Doppler ultrasound, PET scanning, SPECT scanning and, more recently, NIRS have widened our knowledge of general neurolog ical problems. Finally, to achieve our goal of attaining a better understanding of CNS injuries, it is important to assess cerebral cellular metabolism. Magnetic resonance spectroscopy was introduced to achieve this goal. We hope that this book links these different techniques in order to widen our horizon. The future is promising and bound to provide further develop ments, which however can only be understood if we grasp the present level of development. JOSEPH HADDAD Contents 1 Principles of Magnetic Resonance Imaging G. M. BYDDER. . . . . . . . . . . . . 1 2 Magnetic Resonance Imaging: Application to the Neonatal Period D. CHRISTMANN and 1. HADDAD . . . . . . . . . . . . . .. 17 3 Ultrasound C. L. FA WER and A. CALAME 79 4 Cerebral Doppler in the Neonate 1. MESSER . . . . . . . . . . . . . . . . . . . . . . . . . 107 5 Magnetic Resonance Spectroscopy E. B. CADY, 1. HENNIG, and E. MARTIN . . . . . . . . . . . . 117 6 Near Infrared Spectroscopy 1. S. WYATT and D. T. DELPY . . 147 7 Single Photon Emission Computed Tomography of the Brain Perfusion in Neonates 1. HADDAD, A. CONSTANTINESCO, and B. BRUNOT. . . . .. . 161 8 Positron Emission Tomography in the Study of Neonatal Brain D. I. ALTMAN and 1. 1. VOLPE 171 Subject Index . . . . . . . . 183 List of Contributors D. I. ALTMAN, M. B., B. Ch., A. CONSTANTINESCO, M. D., Ph. D., Assistant Professor, Washington Prof. University School of Medicine Service de Medicine Nuc1eaire St. Louis Children's Hospital Hospital University of Strasbourg 400 S. Kingshighway Blvd. Hopital de Hautepierre St. Louis, MO 63110, USA 67098 Strasbourg Cedex, France B. BRUNOT, M. D. D. T. DELPY, Ph. D. Service de Medecine Nuc1eaire Departments of Paediatrics Hospital University of Strasbourg and Medical Physics Hopital de Hautepierre and Bioengineering 67098 Strasbourg Cedex, France University College & Middlesex School of Medicine G. M. BYDDER, Prof. Rayne Institute N.M.R. Department University Street Hammersmith Hospital London WCIE 6JJ, Du Cane Road United Kingdom London W12 OHS, C. L. FAWER, M.D., Ph.D. United Kingdom Division de Neonatologie E. B. CADY, Ph. D. Service de Pediatrie Department of Medical Physics Centre Hospitalier Universitaire and Bio-Engineering Vaudois University College London 1011 Lausanne, Switzerland 1st Floor Shropshire House J. HADDAD, M. D. 11-20 Capper Street Hospices Civils de Strasbourg London WCIE 6AJ, Service de Pediatrie II United Kingdom Medecine et Reanimation du Nouveau-Ne A. CALAME, M. D., Prof. Avenue Moliere Division de Neonatologie 67098 Strasbourg Cedex, France Service de Pediatrie Centre Hospitalier Universitaire J. HENNIG, Ph. D. Vaudois Radio logische U ni versi ta tsklinik 1011 Lausanne, Switzerland ChirurgiejKernspintomographie Hugstetter Str. 55 D. CHRISTMANN, M. D. W-7800 Freiburg i.Br., FRG Hospices Civils de Strasbourg Radiopediatrie - Service de E. MARTIN, M. D. Radiologie II Magnetresonanz Centre Hospitalier Universitaire de Kinderspital Zurich Hautepierre - Strasbourg Steinwiesstr. 75 67098 Strasbourg Cedex, France 8032 Zurich, Switzerland x List of Contributors 1. MESSER, M. D., Prof. 1. S. WYATT, M.D. Service de Neonatologie, Medecine Departments of Paediatrics et Reanimation du Nouveau-Ne and Medical Physics Pediatrie II and Bioengineering Centre Hospitalier Universitaire de University College & Middlesex Hautepierre - Strasbourg School of Medicine Avenue Moliere Rayne Institute 67098 Strasbourg Cedex, France University Street London WCIE 6JJ, 1. 1. VOLPE, M.D. United Kingdom Bronson Crothers Professor of Neurology Harvard Medical School Neurologist-in-Chief Children's Hospital Boston, MA 02115, USA 1 Principles of Magnetic Resonance Imaging G. M. BYDDER CONTENTS were first published in 1980 by Hawkes et al. The subject has evolved rapidly and 1.1 Introduction 1 there is now a large text devoted solely to 1.2 Principles of MRI . 1 MRI in children (Cohen and Edwards t .2.1 Basic Physics . . . t 1990). 1.2.2 Localization of the MRI Signal . 3 1.2.3 Instrumentation. . . . . . . 4 t .2.4 Image Parameters . . . . . . 4 1.2.5 The Principal Pulse Sequences 10 1.2 Principles of MRI 1.3 Contrast Agents 15 1.4 Hazards and Safety 15 1.2.1 Basic Physics References 16 MR describes the phenomenon whereby the nuclei of certain atoms, when placed in a magnetic field, absorb and emit rf energy of a specific frequency. The spec 1.1 Introduction trum of absorbed or emitted rf energy depends upon the nucleus under observa Magnetic resonance imaging (MRI) is a tion and its chemical environment. new noninvasive method of mapping the Nuclei suitable for MRI are those internal structure of the body which com which have an odd number of protons or pletely avoids the use of ionizing radia neutrons and therefore possess a net tion and appears to be without hazard. It charge and have angular momentum. As employs radio frequency (rf) radiation in a result of the combination of charge and the presence of carefully controlled mag angular momentum, these nuclei behave netic fields in order to produce high qual as magnetic dipoles. Almost all images ity images of the body in any plane. It produced to date have been of the nucle usually displays the distribution of hy ar magnetism of the hydrogen nucleus drogen nuclei and parameters relating to (or proton), which is a particularly fa their motion in water and lipids. vourable nucleus from the MRI stand The phenomenon of MR was de point and is present in virtually all bio scribed independently by Bloch and Pur logical materials. Other naturally occur cell in 1946 and for their discovery they ring magnetic nuclei whiceh are of interest were jointly awarded the nobel prize for ienclude phosphorus 1 P), sodium physics in 1952. Since its discovery, MR e3Na), carbon (13C) and potassium has been used extensively as a laboratory 9K). method for studying the properties of The proton can be regarded as a small, matter at the molecular level. freely suspended bar magnet spinning The use of MR for imaging required a rapidly about its magnetic axis. When a method for spatial localization. In 1973 group of protons are placed in a uniform Lauterbur showed that this could be magnetic field, their magnetic moments done by applying a linearly varying mag experience a couple tending to turn them netic field to the body. Clinical images parallel to the direction of the field. In a 2 G. M. Bydder Fig. 1.1. MRI scanner based on a cryogenic field; for protons in a field of 1 T, it is magnet. The x, y and z axes are labelled 42.6 MHz. This relationship is expressed as the Larmor equation: /= yB (1.1) strong magnetic field, many more of these nuclear magnetic dipoles align with where/is the resonant frequency, y is the the applied static magnetic field in the gyro magnetic ratio and B is the applied direction of the field rather than against field. it. This produces a net magnetization in If a pulse of oscillating rf from a coil is the direction of the field and convention imposed on a group of protons in a mag ally defines the z axis, which is generally netic field, there is a strong interaction or along the longitudinal axis of the patient resonant effect, providing that the fre in an MRI machine (Fig. 1.1). quency of the oscillator is equal to the The strong magnetic field, which must precession frequency of the protons. This be homogeneous over a volume large is called magnetic resonance and mani enough to contain the human body in an fests itself in the following way: rf energy MRI machine, is provided by a resistive, is absorbed from the transmitter coil permanent or superconducting magnet. which causes the motion of the elemen Magnetic field strengths used for clinical tary magnets to be disturbed and the di imaging currently range from 0.02 to 4 T. rection of the total nuclear magnetiza Since the nuclei are spinning, they re tion to be altered. The net magnetization spond to the magnetic couple like a gyro along the z axis is deviated through an scope and their axes are tilted so that angle which depends upon the strength they come to rotate at exactly the same and duration of the pulse of the rf mag frequency about the magnetic field direc netic field. So-called 90° and 180° pulses tion in a movement known as precession. are commonly used. These rotate the The frequency of precession is directly magnetization in the z direction through proportional to the applied magnetic 90° and 1800, respectively. After the dis- Principles of Magnetic Resonance Imaging 3 turbance induced by the applied pulse or Variations in the timing of the rf pulses pulses, the magnetization returns to its in these pulse sequences may produce equilibrium position along the z axis in marked differences in image contrast. an exponential manner, and, as it does so, the changing magnetization induces a small voltage in a receiver coil which sur 1.2.2 Localization of the MRI Signal rounds the patient. The electrical signal picked up follow In addition to information at the molecu ing an rf pulse is known as the free in lar level, the MRI signal can also be used duction decay (FID). The magnitude and to provide macroscopic spatial informa length of the FID is determined by the tion. The resonant frequency is propor nuclear relaxation times, which reflect tional to the strength of the magnetic molecular motion. field. If a linearly increasing gradient is The first of these relaxation times, T1, applied in one direction, then the fre or the longitudinal relaxation time, is the quencies of the components of the body time taken by the system of nuclei to re being studied will increase with distance. turn to thermal equilibrium after the rf Each volume element in the body is pulse. The second relaxation time, Tz, or therefore labelled by having a different the transverse relaxation time, is the resonant frequency for the protons with characteristic decay time of the FID and in it. The resulting complicated FID sig is due to the irreversible dephasing of the nal is digitized and frequency analysed in initially coherent precession of individual a computer using a mathematical tech protons which follows the rf pulse. In nique known as Fourier analysis. liquids or systems containing mobile pro If an additional gradient magnetic tons, TzlTl is approximately 1, whereas field is applied prior to the detection of in solids TzlTl is very small. Unlike com the signal, differences in the phase of the puterized tomography (CT) images in local nuclear signals are produced. By us which contrast is determined by differ ing a series of phase encoding gradients ences in one parameter (the linear X-ray of different strengths, the spatial distri attenuation coefficiency /1), multiple bution of signals along a perpendicular parameters influence the MRI signal in gradient direction can also be obtained. cluding proton density, Tl and Tz. In This is the basis of the widely employed addition, flowing material within the im two-dimensional Fourier transform age plane alters contrast. Tl and Tz vari method of imaging. ations between tissues are usually very The rf radiation from the transmitter much greater than variations in proton coil cannot be collimated into a narrow density; thus, images with greater depen beam as can X-rays. There is, therefore, dence on Tl or Tz have greater contrast. a fundamental difference in the method The principal pulse sequences are: of selecting the slice to be imaged. A gra dient field is applied during excitation by 1. Partial saturation (PS) or saturation an rf pulse which contains a predeter recovery (SR) which typically utilizes a mined narrow band of frequencies. Only 90° rf pulse but can use a greater or those regions in which the local resonant smaller pulse. frequency falls within the range of fre 2. Spin echo (SE) which utilizes a 90° quencies determined by the gradient field pulse followed at time TE/2 by an 1800 and corresponding to that of the rf pulse pulse. At a further time, TEI2, an echo are excited. In this way imaging can be of the original signal is detected. restricted to a particular slice of the de 3. Inversion recovery (lR) which utilizes sired thickness. a 180° pulse followed at time TI by a 90° pulse.
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