Renal scintigraphy has several uses. It can measure the function of an apparently healthy kidney prior to removing the other diseased kidney. This is necessary to know because if the remaining kidney is not functioning at a livable level, surgery would not be a viable option. A tracer is administered intravenously and images are taken at various times. Bone scans are based on the principal that healthy bones will incorporate certain bone tracers into their structure.
Healthy bones are dynamic.
Calcium, for instance, is constantly being removed from bone and replaced. The distribution of tracers in bones depends on the rate of this bone turnover and bloodflow. The bone scan reveals the changes in the metabolism of the bone more than actual changes in the bone structure. Bone scintigraphy compliments but does not replace survey radiography. The changes in scintigraphy usually proceed the changes noted on the x-rays since the bone's metabolism usually changes before the bone's structure changes.