Mean Transit Time: Proof and Esophageal Example

The transit of radioactive tracers in human systems provides information of physiologic and diagnostic importance. A simple, non-technical proof is offered for the formula for computation of mean transit time as area/height of a time-activity curve. It is specifically applicable to esophageal transit, and may also serve to illuminate other uses in nuclear medicine. The alternative centroid formula for mean transit time differs in meaning but is compatible with the area/height formula. Considerations regarding mean transit time suggest ways to determine the attenuation of radioactivity that affects a compartment under study.