A bone scan is a test that uses nuclear imaging to helps diagnose and track several types of bone disease. Nuclear imaging involves using small amounts of radioactive substances (radiotracers), a special camera that can detect the radioactivity and a computer to see structures such as bones inside the body. The tracer is absorbed more by cells and tissues that are changing. As a result, a bone scan can be used to find the source of unexplained skeletal pain, a bone infection or a bone injury that can't be seen on a standard X-ray. A bone scan can also be an important tool for detecting cancer that has spread (metastasized) to the bone from the tumor's original location, such as the breast or prostate. A three phase bone scan is used to diagnose a fracture when it cannot be seen on an Xray. It is also used to diagnose bone infection, bone pain, osteomyelitis, as well as other bone diseases.