A bone scan involves injecting a radioactive chemical, called a tracer, into your blood. A technician takes pictures using special imaging equipment that detects the tracer as it circulates through your blood stream. Accumulations of the tracer show up as dark areas in the bone scan. The tracer builds up in bone "hot spots." Hot spots are areas of bone cells that are rapidly turning over. This occurs in such situations as compression fractures, osteoporosis, overuse, and bone tumors. Locating hot spots helps your doctor make a diagnosis and develop a treatment plan.