A bone scan is a test that identifies new areas of bone growth or breakdown. It can be done to evaluate damage to the bones, detect cancer that has spread (metastasized) to the bones, and monitor conditions that can affect the bones (including infection and trauma).
During a bone scan, a small amount of radioactive substance (radionuclide) is injected into the bloodstream. A camera takes pictures of the location of the radioactive substance in the bone. Areas that absorb little or no amount of tracer appear as dark or "cold" spots. This could show a lack of blood supply to the bone or certain types of cancer. Areas of abnormal bone collect a lot of the radioactive substance and show up as "hot" spots on the picture. Hot spots may mean problems such as arthritis, a tumor, a fracture, or an infection. A bone scan can often detect a problem days to months earlier than a regular X-ray test.