The ocean has entranced mankind for as long as we have gazed upon it, traversed it, dived into it, and studied it. It remains ever changing and seemingly never changing. Each wave that progresses through the. imme diate surf zone on every coast is strikingly different, yet the waves come again and again, as if never to end. The seasons come with essential reg ularity, and. yet each is individual-whatever did happen to that year of the normal rainfall or tidal behavior? This fascination with the currents of the ocean has always had a most immediate practical aspect: shipping, transportation, commerce, and war have depended upon our knowledge, when we had it, and floundered on our surprising ignorance more often than we wish to reflect. These important practical issues have commanded attention from commercial, academic, and military research scientists and engineers from the earliest era of organized scientific investigation. The matter of direct and insistent investigation was from the outset the behavior of ocean currents with long time scales; namely, those varying on annual or at least seasonal cycles. Planning for all the named enterprises depended, as they still do, of course, on the ability to predict with some certainty this class of phenomena. That ability, as with most physical sci ence, is predicated on a firm basis of observational fact to establish what, amorig the myriad of mathematical possibilities, is chosen by Nature as her expression of fact."

In recent decades imaging has proved one of the most rapidly expanding areas of medicine. The present day trainees entering radiology are no longer trained by radiologists who cover and are well informed on most aspects of their specialty as was the case with previous generations. Instead they encounter a confusing array of subspecialists divided both by systems and by techniques. The system specialists include neuroradiologists. vascular radiologists. gastrointestinal radiologists. chest radiologists. and skeletal radiologists. Technique specialists include experts in nuclear medicine. ultrasound. computed tomography and magnetic resonance. and there are subspecialists in both groups. not to mention others like pediatric radiologists who fit into neither classification. It is our experience that this plethora of experts each with his own individual approach is bewildering and intimidating to the novice radiologist. The numerous monographs on individual subjects and tech niques and the large textbooks so valuable to the more advanced radiologist are also confusing and unhelp ful to the new recruit. It was for these reasons that we decided to embark on this new Short Textbook. The aim was to produce a concise and integrated volume which could provide the beginner with a balanced and realistic view of the true place of different imaging techniques in current practice. Details of technique are generally excluded; most will be inevitably absorbed with increasing practical experience. The emphasis throughout is on clinical usage. and the relative and often changing importance of different methods in specific clinical contexts.