A Bone scan or bone scintigraphy is a nuclear scanning test to find certain abnormalities in bone which are triggering the bone's attempts to heal. It is primarily used to help diagnose a number of conditions relating to bones, including: cancer of the bone or cancers that have spread (metastasized) to the bone, locating some sources of bone inflammation (e.g. bone pain such as lower back pain due to a fracture), the diagnosis of fractures that may not be visible in traditional X-ray images, and the detection of damage to bones due to certain infections and other problems.
Nuclear medicine bone scans are one of a number of methods of bone imaging, all of which are used to visually detect bone abnormalities. Such imaging studies include magnetic resonance imaging (MRI), X-ray computed tomography (CT) and in the case of 'bone scans' nuclear medicine. However, a nuclear bone scan is a functional test, which means it measures an aspect of bone metabolism, which most other imaging techniques cannot. The nuclear bone scan competes with the FDG-PET scan in seeing abnormal metabolism in bones, but it is considerably less expensive.
Nuclear bone scans are not to be confused with the completely different test often termed a "bone density scan," DEXA or DXA, which is a low exposure X-ray test measuring bone density to look for osteoporosis and other diseases where bones lose mass, without any bone re-building activity. The nuclear medicine scan technique is sensitive to areas of unusual bone re-building activity because the radiopharmaceutical is taken up by osteoblast cells which build bone. The technique therefore is sensitive to fractures and bone reaction to infections and bone tumors, including tumor metastases to bones, because all these pathologies trigger bone osteoblast activity. The bone scan is not sensitive to osteoporosis or multiple myeloma in bones, and therefore other techniques must be used to assess bone abnormalities from these diseases.