This book is written as both a text and a reference book. It contains numerous images from the biological sciences and clinical practice, tables, graphs, and fig­ ures, as well as exercises that are worked out to aid the reader in understanding principles or solving problems. In some cases, derivations are placed in appen­ dices so as not to break up the flow of the subject matter in the text. The book is intended for a broad audience interested in molecular imaging with positron emission tomography (PET). It is expected that the readers will range from undergraduate, graduate, and medical students to residents, physi­ cians, and scientists with backgrounds from various physical, biological, and medical specialty areas. Each chapter presents material in a straightforward man­ ner that is well illustrated and explained. Because of the diverse audience for the book, certain chapters or sections of chapters will be of more interest than oth­ ers to certain segments of the readership. Chapter 1 introduces the fundamental physics upon which PET imaging sys­ tems is based and discusses in detail the technologies and methods used to pro­ duce PET images. The chapter starts out by reviewing the physics of positron emission and annihilation and explains how positron range and photon non­ colinearity in coincidence detection place certain limits on spatial resolution.