This book is not intended as a general text on MRI. It is written as an intro duction to the field, for nonexperts. We present here a simple exposition of certain aspects of MRI that are important to understand to use this valuable diagnostic tool intelligently in a clinical setting. The basic principles are presented nonmathematically, using no equations and a minimum of symbols and abbreviations. For those requiring a deeper understanding of MRI, this book will help facilitate the transition to standard texts. Chapters 1 through 4 provide a general introduction to the phenomenon of nuclear magnetic resonance and how it is used in imaging. Chapter 1 discus ses magnetic resonance, using a compass needle as an example. In Chapter 2, the transition to the magnetic resonance of the atomic nucleus is made. Chapter 3 describes the principles of imaging. In Chapter 4, the terms T 1 and T 2 are described and their relationship to tissue characterization; the fun damental role of thermal magnetic noise in T 1 and T 2 is discussed.

An Advanced Study Institute on Ultrasonics in Medical Diagnosis was held in Milan, Italy, from 10 to 15 June 1974. This ASI was of a short five-day duration and limited to cardiac diagnosis by ultra sound only. Since that time, the field of diagnostic imaging in medicine has literally exploded with new and improved means of medical diagnosis such as computed tomography, microwaves, nuclear magnetic resonance and other sophisticated techniques. These developments have enabled medical practitioners to make diagnoses with a minimum of danger to the patient, and a maximum of accuracy never before possible, and represent a multi-quantum advance over the early state-of-the-art presented at the 1974 ASI. Since then, several meetings have taken place on these individual topics to bring together experts who presented their latest research results, but none have discussed the entire field of diagnostic imaging in medicine in one meeting nor have they had the teaching character of an Advanced Study Institute. The art and science of medicine have been altered repeatedly during the eight year interval since the last ASI. Today's clinician must be part technologist and must be enough of an investigator to understand and appreciate the scientific method. The current complex advances in instrumentation and pharmacology have had a marked effect on how medicine is practiced. There was, therefore, an urgent need to bring the entire field of imaging in medicine to one teaching podium where the many advances of the last six or seven years could be reviewed.

This atlas is a selection of roentgenograms of patients who visited the radiology departments at the University Hospital in Leiden between 1970 and 1978, the Free University Hospital in Amsterdam in 1979, and the radiology department at the Indiana University Medical School in Indianapolis in 1977. The most common radiological abnormalities of the small intestine are illustrated clearly, unhindered by flocculation or segmentation of the contrast fluid. The authors believe this book is a definite contribution to the goal of precise early small bowel diagnosis. However, the key to good diagnosis is not only a superb examination technique, but also the knowledge, the character, and the personal perfectionism of the physician. If these factors are optimal, then the best possible roentgenographic series will be obtained - at least as far as the technique is concerned. All patients illustrated here were examined by using the enteroclysis technique. With this method of small bowel examination, the contrast fluid is administered via an infusion directly into the duodenum instead of orally. The infusion method has added a new dimension to the usual radiological examination of the small intestine. This method is also especially suited for the comparative evaluation of motility, and the study of disturbed motility. Throughout the course of the examination, the technique can be adapted to special situations at any given moment and can be modified to produce precise diagnostic roentgenograms and diagnosis.

There are two important reasons for publishing this new series entitled "Advances and Technical Standards in Neurosurgery": 1. the lack of any organized common European postgraduate training system for young neurosurgeons and 2. the language barriers, which impede the exchange of neurosurgical findings in Europe more than in other parts of the world. The fact that the English language is well on the way to becoming the international medium at European scientific conferences is a great asset in terms of mutual understanding. Therefore the Editors have decided to publish all contributions III English, regardless of the native language of the authors. All contributions are submitted to the entire editorial board before publication of any volume. Our series is not intended to compete with the publications of original scientific papers in other neurosurgical journals. Our intention is, rather, to present fields of neurosurgery and related areas in which important recent advances have been made. The contributions are written by specialists in the given fields and constitute the first part of each volume. In the second part of each volume, we publish detailed descriptions of standard operative procedures, furnished by experienced clinicians; in these articles the authors describe the techniques they employ and explain the advantages, difficulties and risks involved in the various procedures. This part is intended primarily to assist young neurosurgeons in their postgraduate training. However, we are convinced that it will also be useful to experienced, fully trained neurosurgeons.

J.J. Broerse, Radiobiological Institute TNO, Rijswijk, The Netherlands, and T .J. MacVittie, Armed Forces Radiobiology Research Institute, Bethesda, MD, USA. During the past decade, relatively few new studies have been initiated on the response of different species to high-dose, total-body irradia- tion. For information on the LDSO/30d (the dose which produces 50 percent lethality within 30 days), one is generally referred to the older literature (e. g., Bond, Fliedner and Archambeau, 1965). Compari- son of experimental data reveals considerable variations in LDSD values even after total-body irradiation with conventional X rays, ranging from 4 to 6 Gy in the monkey, 7.1 to 9 Gy in the rat and from 6.4 to 9 Gy in the mouse (see also Hall, 1978). Part of the discrepancy in the LDso values can possibly be attributed to inadequacies in the dosimetry procedures and exposure arrangements employed. As far as clinical experience is concerned, there is now an appreciable amount of information available about the effect of total- body irradiation as a conditioning treatment for bone marrow transplan- tation in patients suffering from leukaemia or aplastic anaemia. The results from different centres, including the incidence of complications such as radiation pneumonitis, are considerably different. This can part I y be connected with the application of different radiation sched- ules: large single dose versus fractionated or protracted irradiation.

As an addition to the European postgraduate training system for young neurosurgeons we began to publish in 1974 this series devoted to Advances and Technical Standards in Neurosurgery which was later sponsored by the European Association of Neurosurgical Societies. The fact that the English language is well on the way to becoming the international medium at European scientific conferences is a great asset in terms of mutual understanding. Therefore we have decided to publish all contributions in English, regardless of the native language of the authors. All contributions are submitted to the entire editorial board before publication of any volume. is not intended to compete with the publications of original Our series scientific papers in other neurosurgical journals. Our intention is, rather, to present fields of neurosurgery and related areas in which important recent advances have been made. The contributions are written by specialists in the given fields and constitute the first part of each volume. In the second part of each volume, we publish detailed descriptions of standard operative procedures, furnished by experienced clinicians; in these articles the authors describe the techniques they employ and explain the advantages, difficulties and risks involved in the various procedures. This part is intended primarily to assist young neurosurgeons in their post graduate training. However, we are convinced that it will also be useful to experienced, fully trained neurosurgeons."

This book is not meant to be a textbook or a handbook of phlebography of the lower limbs. It is an atlas aimed only at teaching one how to read an interpret phlebograms, and is of considerable importance as it represents the standard investigatory method used to check the reliability of other diagnostic methods concerning venous circulation. Regarding diagnosis, nothing is more certain than the phlebographic demonstration of a thrombus; moreover, even if the thrombus is not demonstrable, as in certain phlebites. it is still possible to establish the diagnosis with adequate knowledge of the radio anatomy of the non-opacified veins and the demonstration of marked collateral circulation. Therefore this investigation must be carried out very carefully with particular attention to interpretation. The technique was first used in man in 1923 and is now employed world wide; better tolerated contrast materials render it almost innocuous; the occurrence of very few incidences of non-tolerance does not diminish the value of this method. We have purposely reduced the text to legends of the illustration and withheld the bibliography in so far as it is meant to be a teaching program by way of pictures without any reference to past or present publications.

There are two important reasons for commencing this new series of publi cations entitled "Advances and Technical Standards in Neurosurgery" 1. the lack of any organized common European postgraduate training system for young neurosurgeons and 2. the language barriers, which impede the exchange of neuro surgical findings in Europe more than in other parts of the world. The fact that the English language is well on the way to becoming the international medium at European scientific conferences is a great asset in terms of mutual understanding. Therefore the Editors have decided to publish all contributions in English, regardless of the native language of the authors. All contributions are submitted to the entire editorial board before publi cation of any volume. Our series is not intended to compete with the publications of original scientific papers in other neurosurgical journals. Our intention is, rather, to present fields of neurosurgery and related areas in which important recent advances have been made. The contributions will be written by specialists in the given fields and will constitute the first part of each volume."

Proceedings of the 9th Conference, Washington D.C., 10-14 June 1985 Sponsored by the Clinical Center and the Fogarty International Center of the National Institutes of Health, Bethesda, Maryland, USA

As an addition to the European postgraduate training system for young neurosurgeons we began to publish in 1974 this series devoted to Advances and Technical Standards in Neurosurgery which was later sponsored by the European Association of Neurosurgical Societies. The fact that the English language is well on the way to becoming the international medium at European scientific conferences is a great asset in terms of mutual understanding. Therefore we have decided to publish all contributions in English, regardless of the native language of the authors. All contributions are submitted to the entire editorial board before publication of any volume. Our series is not intended to compete with the publications of original scientific papers in other neurosurgical journals. Our intention is, rather, to present fields of neurosurgery and related areas in which important recent advances have been made. The contributions are written by specialists in the given fields and constitute the first part of each volume. In the second part of each volume, we publish detailed descriptions Of standard operative procedures, furnished by experienced clinicians; in these articles the authors describe the techniques they employ and explain the advantages, difficulties and risks involved in the various procedures. This part is intended primarily to assist young neurosurgeons in their post graduate training. However, we are convinced that it will also be useful to experienced, fully trained neurosurgeons."

Master of all endocrine activity and executive organ of one's quality of life, the pituitary gland is tightly lodged in the" turkish saddle. " As a bony container, the sella turcica is to the hypophysis what the skull is to the brain; it can therefore be looked upon as a little vault within the cranial vault. Just as the cranium is moulded by the growth of the brain, so is the sella fashioned by its content. It becomes locally enlarged in response to expanding intrasellar lesions, and it tends to return to its original size and shape upon their removal or destruction. Pituitary adenomas have in the past been diagnosed upon enlargement of the sella turcica. In the past decade, as a direct result of interdisciplinary coopera- tion, we have learned that tiny adenomas, the immediate cause of some cases of acromegaly, amenorrhea-galactorrhea syndrome, or Cushing's disease, can exist with minimal or no observable effect on the size of the sella. The break- through started when radioimmunoassay, as a new method of accurately measur- ing specific hormonal output, indicated selective pituitary oversecretions in pa- tients with normal-sized sellae. Neurosurgeons highly skilled in the transsphenoi- dal approach with the surgical microscope were obliged to operate on some of these patients and confirmed the presence of tiny oversecreting adenomas in their pituitary glands.

In this age when we are witnessing a veritable explosion in new modalities in diagnos tic imaging we continue to have a great need for detailed studies of the vascularity of the brain in patients who have all types of cerebral vascular disease. Much of the understanding of cerebral vascular occlusive lesions which we developed in the last two decades was based on our ability to demonstrate the vessels that were affected. Much experimental work in animals had been done where major cerebral vessels were obstructed and the effects of these obstructions on the brain observed pathologically. However, it was not until cerebral angiography could be performed with the detail that became possible in the decades of the '60 's and subsequently that we could begin to understand the relationship of the obstructed vessels observed angiographically to the clinical findings. In addition, much physiologic information was obtained. For instance, the concept ofluxury perfusion which is used to describe non-nutritional flow through the tissues was observed first angiographically although the term was not used until LASSEN described it as a pathophysiological phenomenon observed during cerebral blood flow studies with radioactive isotopes. The concept of embolic occlusions of the cerebral vessels as against thrombosis was clarified and the relative frequency of thrombosis versus embolism was better understood. The concept of collateral circulation of the brain through so-called meningeal end-to end arterial anastomoses was vastly better understood when serial angiography in obstructive cerebral vascular disease was carried out with increasing frequency."

In January 1995, 300 participants from Asia, USA, and Europe lively discussed the "State of the Art and Future Aspects of CT" in Peking, China. The workshop was designed to cover all essential aspects of modern CT imaging including the historical development, different techniques, contrast agents, organ systems, and indications. The comparative evaluation of CT versus MRI and ultrasound was a central topic. Additionally, a special session was dedicated to "Angiography Tomorrow." This book summarizes the state of the art in both conventional and spiral CT imaging and provides some suggestions as for the future role of the method.

This book reflects the views of an international faculty and provides an authoritative appraisal of modern radiology. It represents the sec ond volume in a planned series of competent overviews, and is mod eled on the successful first volume, Radiology Today, which was enthu siastically received by an international readership. We were encour aged by the comments we received to continue blending the latest ad vances in radiology with comprehensive teaching material concerning modern radiological practice. The Radiology Today 1982 meeting again brought together outstanding radiologists from Europe and North America for the purpose of sharing their experiences and their viewpoints of the current position and opportunities of imaging in medicine. Updating his/her knowledge of advances in medical imaging has be come an integral part of continuing medical education for every radiol ogist. Because all imaging modalities are continuously being refined, new clinical applications develop and frequently replace more com plex or more invasive procedures. Also, the relationship of imaging procedures to each other changes constantly, and with it the configura tion of critical diagnostic pathways for investigation of clinical signs and symptoms. To recognize this trend is important, because it is ex panding the role of the radiologist: our involvement in active guidance to the point of the patient's diagnostic workup has increased signifi cantly where it has become strategic."

The eontinual growth of radiologie information makes it inereas- ingly diffieult for the praetitioner to maintain eurrent clinieal knowledge. Radiologie textbooks eontaining mueh material for the praetieing clinieian are often impossible to review thoroughly. Such radiographie texts deseribing the hand as a window to the understanding of systemie disease are available, but there has been an absence of books whieh present an easily assimilated synopsis of this material. Professor Thijn has elegantly presented all the major and many minor features of diseases and eonditions that affeet the skeleton, using hand roentgenograms as a window. He has also included numerous illustrations of key assoeiated roentgeno- graphie manifestations elsewhere in the body. His organized pre- sentation of eaeh entity, including introductory remarks, radio- graphie findings in the hand and other sites, differential diagno- sis, and key referenees, forms a strueture through whieh an ap- propriate evaluation of a clinieal ease may be made. The eoneise synopsis of eaeh disease entity, weIl illustrated by superb roentgenograms, provides an exeellent strueture for both the student first learning about such eonditions and the praetitioner researehing an explanation for partieular roentgeno- graphie findings. Professor Thijn has attempted, and I believe has sueeeeded admirably, to provide a souree from whieh a student or praeti- tioner of radiology may readily arrive at a differential diagnosis of an observed radiographie feature. LOUIS A. GILULA, M.D.

The purpose of this book is to explain the current state of the art in radiological examination, interpretation, and understanding of colonic disease. The radiologic aspects of colon disease are combined here with clinical information to serve both beginners and advanced students. Major emphasis has been placed on technique for those radiologists, residents, and technologists first undertaking modern gastrointestinal radiographic techniques. The essentials of technique are stressed so that the reader obtains a clear understanding of colon disease based on sound practical information. We believe this book is a thorough and practical text of particular interest to clinical radiologists and gastroenterologists in their everyday practice, and also for teachers, residents and medical students. Digital examination and sigmoidoscopy are the first procedures in examination of the colon. Then, the radiologic examination is the next most important procedure. Endoscopy and biopsy play a compli mentary role to the radiological examination. The barium enema reveals quickly and early the overall status of the colon and it can then guide endoscopy and biopsy together with subsequent treatment. Surely, if the lesion is not detected our clinical, radiologic, endoscopic, and therapeutic skills are of no use."

There have been significant advances in the treatment of sarcomas in the past several years. Further, different clini cal treatment programs are being advocated in different areas including surgery alone, surgery with preoperative or post operative chemotherapy, surgery with different radiotherapy modalities, with each investigator espousing his own treat ment program. On the other side, there is the question of whether these treatment programs are offering better results or whether the natural history of sarcomas has changed. The International Symposium on Sarcomas was held at Innisbrook Resort, Tarpon Springs, Florida, October 8-10, 1987. This was the first international symposium to date involving all of the disciplines treating sarcomas including pathologists, orthopaedic surgeons, general surgeons, medical oncologists, pediatric oncologists, and radiation oncol ogists. The Symposium brought together a number of special ists working in the clinical field of sarcomas for a presen tation of their specific treatment programs and their results. The presentations were followed by panel discussions to stimulate educational debate as to the different forms of treatment for sarcomas and to formulate some conformity in control of disease, control of spread, and ultimate function for the patient. James R. Ryan, M.D."

Over the past decade, techniques have been developed and implemented to observe metabolism noninvasively in localized regions of intact, living experimental animals and humans through the use of magnetic resonance spectroscopy (MRS). At the same time, magnetic resonance imaging (MRI) techniques developed in the 1970s and refined in this decade have been increasingly applied as a powerful clinical tool to probe human anatomy. Because of the unusual metabolic and physiologic characteristics of malignant tissues, oncology has been one of the primary focuses of the application of both MRS and MRI. Although considerable progress has been made in oncologic applications of magnetic resonance (MR), further research is needed to realize the full potential of MR in this area. Consequently, the 21st Annual Detroit Cancer Symposium entitled "Magnetic Resonance in Experimental and Clin ical Oncology" was organized to provide a forum for researchers in the field to report the state of the art of MRS and MRI in oncol ogy, to discuss future goals for MRS and MRI in oncology, and to define the research needed to meet those goals. The major emphasis of the symposium was on MRS due to both the recent widespread availability of clinical MRS instrumentation and the extensive amount of animal MRS research performed over the past half decade.

It Itis is 1984, 1984, a a year year immortalized immortalizedby by George GeorgeOrwell Orwell some some35 35 year year ago. ago. In In 1949, 1949, he he prophesized prophesized a a world worlddominated dominated by by television television images images and andelectronic electronic communica communica tions. Orwell's vision of an incredible technologic revolution is the reality of the tions. Orwell'svisionofanincredibletechnologicrevolutionistherealityofthe 1980's. 1980's. Over Over the the past past three threedecades, decades, this this technical technicalexplosion explosion has has impacted impacted on on all all levels levelsof of society, society, including including the the practice practice of ofMedicine. Medicine. In 1949, the cardiologist had available to him only his stethoscope, the chest In1949, thecardiologisthadavailabletohimonlyhisstethoscope, thechest roentgenogram, roentgenogram, the theelectrocardiogram, electrocardiogram, and and his hisclinical clinical astuteness. astuteness. In In 1984, 1984, the the cardiologist still requires great clinical skills, but also has available to him echo cardiologiststillrequiresgreatclinicalskills, butalsohasavailabletohimecho cardiography, cardiography, radionuclide radionuclideperfusion perfusion and and functional functional tests, tests, digital digital radiography, radiography, computed computed tomography, tomography, positron positronemission emission tomography, tomography, and and nuclear nuclearmagnetic magnetic resonance resonanceimaging. imaging. These These imaging imagingmodalities modalities are are the theresult result of ofthe the development developmentof of the the digital digitalcomputer, computer, and and the theexplosive explosive advances advances in in microelectronics. microelectronics. Cardiac Cardiac imaging imaginghas has rapidly rapidlyevolved evolved into intoa a specialized specialized area area of of interest interestshared shared by by cardiolo cardiolo gists, radiologists, engineers, physicists, and statisticians. Our book, Digital gists, radiologists, engineers, physicists, andstatisticians."

Interest in bone densitometry methods has recently experienced a resurgence within the medical community. Physicians have become more interested than ever before in the diagnosis and treatment of degenerative diseases of bone such as osteoporosis. The public perception of osteoporosis and its prevention has been recently heightened. Because osteoporosis is widespread, especially in women, and leads to an increase in fractures in our population, many re searchers and clinicians are strongly motivated in their search for more sensi tive and accurate methods of diagnosis. This book was written for physicians, scientists, engineers, medical phy sicists, and others desiring an introduction or further understanding of this exciting field. Beginning with the early development of x-ray film methods for assessing bone status, the field has steadily grown throughout the years. Novel and interesting devices have been designed for the measurement of bone mass, bone density, cortical thickness, and other parameters of bone changes. Both qualitative and quantitative bone methods are described. The techniques include imaging devices such as CT and radiography as well as fixed point methods in which bone characteristics of a region of interest are analyzed."

"Progress in Medical Imaging" contains a collection of interdisciplinary reviews of subtopics in medical imaging written by internationally known experts. Topics contained in the book include automatic recognition of cells and tissue types in light microscopy, computerized manipulation and assembly of two-dimensional scans of an organ into images of the three-dimensional organ which can be rotated in space, techniques for reducing the image degradation produced by scattering radiation in chest radiography, recent advances in instrumentation, and principles of positron-emission tomography. The final chapters of this book describe the advantages of pseudo-random codes as transmitted signals for ultrasonic flow measurement, imaging, and medium characterization. The primary audience for "Progress in Medical Imaging" includes engineers, physicists, and students engaged in research, development, or applications of medical imaging.

The management of ankle injuries has long been a stumbling block for orthopae dists in training. As a first year resident, I was fortunate to encounter the series of articles by N. Lauge-Hansen and T. Baek Kristensen that classified ankle injuries according to their mechanism. I found this information quite helpful throughout my residency and early years of practice. Several years ago, an attempt was made to summarize this material for the benefit of the orthopaedic house staff of Thomas Jefferson University. It quickly become obvious that such a "manual" would require a great deal of professional illustration and editorial assistance in order to be effective. Almost simulta neously, a fortuitous encounter with Ms. Marie Low (at that time Medical Editor of Springer-Verlag New York Incorporated) provided both the stimulus and the means to present this information in the manner and detail which it deserved. Contributors were carefully selected for their knowledge and experience in particular areas and for their willingness to cooperate in providing a smooth flowing manuscript. This text contains little new material. Rather, it represents an attempt to bring together, under one cover, the wealth of extant information on this subject. Wherever a consensus could not be perceived, conflicting views have been sum marized as objectively as possible. Unfortunately, there are still many aspects of ankle injury for which we have more questions than answers."

This book has been written for radiologists, ophthalmologists, neurologists, neurosur geons, plastic surgeons, and others interested in the evaluation of disorders with ophthalmologic signs and symptoms. It is designed to provide recent knowledge in this area derived from ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). In the past decade, the advent of ultrasonography, computed tomography, and more recently magnetic resonance imaging has provided diagnostic images of the eye, orbit, and brain in a fashion that had been a dream of many prior to the develop ment of these techniques. These newer modes of diagnosis have replaced some previous techniques, such as nuclear medicine imaging and, to some degree, vascular studies and orbitography. There are three sections to this book. The first section is a discussion of the imaging techniques. The second is devoted to the role of these imaging methods in the evaluation of ophthalmic disorders. The last section, dealing with radiotherapy for ophthalmologic tumors, is included because the current imaging techniques are needed for treatment planning. We wish to thank the many people who have assisted us in preparing this manuscript. Among these are many librarians, secretaries, trainees, and photographers. Weare especially indebted to artist Peter Clark for his illustrations and to Mr. Martin Leibo vici, Associate Curator of New York University Medical School and Director of Health Sciences Library of Goldwater Memorial Hospital, New York City. Also, we wish to thank our families for their help and patience."

This book is intended as a short guide to the visualization of the anatomy of the normal brain by means of the NMR tomogram. The first section comprises a brief introduction to the physical and technical aspects of NMR. This is followed by the atlas section, which pursues a number of objectives. On the basis of two important NMR imaging techniques, the spin-echo technique and the inversion-recovery technique, those experi enced in CT are given the opportunity to familiarize themselves with the differences in tissue contrast that exist in NMR scans despite their appar ent similarity to conventional CT scans. The mode of action of the two NMR imaging techniques is explained in the technical introduction. An additional innovation is the possibility of producing sections that are not, as in CT scanning, limited by the body of the patient. The sagittal and frontal sections parallel to the plane of the face can show an unfamiliar, but particularly clear, image of the anatomy of the head and brain com pared with conventional horizontal sections. An anatomical description accompanying every section is provided by way of clarification. A particular advantage of NMR imaging, namely, the absence of ionizing radiation and, thus, an injurious effect on biological systems (Budinger 1981), makes it possible to provide a systematic visualization of a healthy human brain in a living person in three planes, arranged at right angles to one another."

7 Les Houches The purpose of this workshop was to bring together, for the first time, active scientists from very different fields, such as physics, chemistry, physiology and the behavioural sciences, all having a common interest: The interac tion of static magnetic fields with biological and macromolecular matter. As physicists, biologists and medical scientists naturally have different scientific competences, attitudes and abilities, this appeared to be an enterprise of un certain issue. However, it turned out that all participants tried to find (and many succeeded in reaching) a mutual basis of understanding. Thanks to a fair number of outstanding, comprehensive talks and to very active discus sions, most of us, we believe, have substantially enlarged our insight into the actual hard facts within a research area that was considered for a long time - and still remains in many aspects - somewhat controversial. The perhaps most striking and useful reaction to magnetic fields at the supermolecular level is the alignment of biopolymers, proteins, viruses, large assemblies such as retinal rods and membranes when suspended in a solvent, usually water. The ease of alignment depends on the anisotropy of the dia magnetic susceptibility of the constituent groups and bonds and, in addition, on the extent of their mutual orientational order inside a macromolecular assembly. Here very strong fields above I-lOT appear to be necessary, in general, to achieve measurable alignment."