This book explores the mathematics and biology of the biodistribution of radiopharmaceuticals following their introduction into the body, but does so primarily from a clinical perspective - from the point of view of image interpretation and any associated image-derived quantification. All of the equations included in the book relate directly to the biodistribution of radiopharmaceuticals and are clinically useful, either conceptually or because of their value in quantifying a biological parameter, e.g., renal clearance. In particular, the more complex equations are not meant to be solved but instead are intended to provide a conceptual basis for the analysis of clinical images, especially those that are unusual and/or difficult to interpret. The efficacy of every diagnostic and therapeutic nuclear medicine procedure is critically dependent on the biodistribution of the radiopharmaceutical in question over time. This book will enable the reader to gain a sound understanding of the relevant mathematics and biology, and the clinical orientation ensures that it will be of value in enhancing clinical practice.