Nuclear medicine is the bridge between a particular clinical problem and a relevant test using radionuclides. It began as a minor technical tool used in a few branches of medicine, notably endocrinology and nephrology. However, throughout the world it has now become established as a clinical discipline in its own right, with specific training programmes, special skills and a particular approach to patient management. Although the practising nuclear medicine physician must necessarily learn a great deal of basic science and technology, a sound medical training and a clinical approach to the subject remains of fundamental importance. It is for this reason that we have attempted in this book to approach the subject from a clinical standpoint, including where necessary relevant physiological material. There exist many excellent texts which cover the basic science and technology of nuclear medicine. We have, therefore, severely limited our coverage of these aspects of the subject to matters which we felt to be essential, particularly those which have been less well covered in other texts - for example, the contents of Chapter 21 on Quantitation by Royal and McNeil. Similarly, we have included at the end of some chapters descriptions of particular techniques where we and the authors felt that it would be helpful. In order to emphasize the clinical approach of this book we have inverted the traditional sequence of material in chapters, presenting the clinical problems first in each instance.