The material in this volume was prepared and collected over the past four years with the growing realization that a technical revolution was in progress for diagnostic medicine. It became clear that for the wide variety of imaging instruments and methods finding their way into applications for research and clinical medicine, there was a scarcity of reference and text books for the scientist and engineer beginning in the field. Thus what began as a relatively small project for a single volume has grown into certainly two and probably three volumes to adequately cover the field. This first volume is expected to be followed within a few months by a second volume, dealing with diagnostic radiology, and within a year by a third volume, covering most other aspects of medicine that utilize spectra from the ultraviolet through the visible into the near-infrared. The chapters in this book are divided into three groups. The first group deals with nuclear medicine and includes Chapters 1-8. These chapters are arranged to begin with a broad introduction to the subject (Chapter 1) followed by a sequence of four chapters (Chapters 2-5) that provide an in-depth review of the imaging instrumentation developed for the field. Chapter 6 deals with "evaluation" of imaging device per­ formance, while Chapters 7 and 8 discuss two areas of considerable re­ search activity.