Radionuclide-mediated scanning studies, known as an "in vivo" diagnostic method, are performed to measure the amount of a specific radionuclide distributed in the body or specific organs by scanning and imaging. The studies are named for the organ or region of the body to be examined or imaged. The radiopharmaceutical and route used, as well as the time involved to perform the study, are specific to the organ studied. Commonly used radiopharmaceuticals and their tissue sites are listed in Table 20-1. The scanning procedure provides a picture of the location, shape, size, and functional disturbances of an organ. Almost all organs can be scanned for diagnostic information related to the presence of tumors or other abnormalities.