A bone scan is a specialized radiology procedure used to examine the various bones of the skeleton. It is done to identify areas of physical and chemical changes in bone. A bone scan may also be used to follow the progress of treatment of certain conditions. A bone scan is a type of nuclear radiology procedure. This means that a tiny amount of a radioactive substance is used during the procedure to assist in the examination of the bones. The radioactive substance, called a radionuclide, or tracer, will collect within the bone tissue at spots of abnormal physical and chemical change.The radionuclide emits a type of radiation, called gamma radiation. The gamma radiation is detected by a scanner, which processes the information into a picture of the bones. The areas where the radionuclide collects are called "hot spots," and may indicate the presence of conditions such as arthritis , malignant (cancerous) bone tumors , metastatic bone cancer (cancer which has spread from another site, such as the lungs), bone infections , bone trauma not seen on ordinary X-rays, and other conditions of the bone. Bone scans are used primarily to detect the spread of metastatic cancer. Because cancer cells multiply rapidly, they will appear as a hot spot on a bone scan. This is due to the increased bone metabolism and bone repair in the area of the cancer cells. Bone scans may also be used to stage the cancer before and after treatment in order to assess the effectiveness of the treatment.