A radionuclide scan may be done for all sorts of reasons. For example:
A bone scan is a common type. A radionuclide is used which collects in areas where there is a lot of bone activity (where bone cells are breaking down or repairing parts of the bone). So a bone scan is used to detect areas of bone where there is cancer, infection, or damage. These areas of activity are seen as 'hot spots' on the scan picture. See the separate leaflet called Bone Scan for more details.
This is a companion discussion topic for the original article at https://patient.info/treatment-medication/radionuclide-scan-isotope-scan