There has been a great deal of interest in recent years in the development of improved systems for displaying the distribution of radioactive tracers inside the human body. There are a number of diagnostic radioisotope studies that depend on accurate imaging, and physicians have come to rely on some of these studies as a necessary part of a routine workup for certain disorders. Some of the most creative activity has been in the field of dynamic flow studies, i.e. imaging the rapid passage of a bolus of radioisotope through an organ of interest. Dynamic flow studies are of especial interest in studies of highly vascular organs such as the heart, lungs, brain, and kidneys.