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.