A bone scan is a nuclear imaging test that helps diagnose and track several types of bone disease. Your doctor may order a bone scan if you have unexplained skeletal pain, bone infection or a bone injury that can't be seen on a standard X-ray. A bone scan is also 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. 1  Why it's done.