A bone scan uses radiation to make images showing areas of bone where cells are unusually active. Unusually active cells can indicate cancer, bone trauma, infection or other disorders.
First, a radioactive chemical called an isotope is injected into a vein. The isotope enters the bloodstream and travels to the bones, where it emits gamma rays, which are similar to X-rays. A gamma camera can detect gamma rays. A computer analyzes the rays and forms an image (or scan) of the bones. Areas with potential problems send out more intense rays and appear as bright spots on the scan.
A bone scan is painless, except for a mild skin prick to inject the isotope. It takes about three hours for the isotope to travel to the bones. During this time, you usually can leave the facility and return for the scan later, which generally takes about an hour.