A bone scan is an imaging test used to help diagnose problems with your bones. It safely uses a very small amount of a radioactive drug called a radiopharmaceutical. It has also been referred to as a “dye,” but it doesn't stain the tissue. Specifically, a bone scan is done to reveal problems with bone metabolism. A bone scan or bone scintigraphy is a nuclear medicine imaging technique of the bone. It can help diagnose a number of bone conditions, including cancer of the bone or metastasis, location of bone inflammation and fractures (that may not be visible in traditional X-ray images), and bone infection (osteomyelitis) Nuclear medicine provides functional imaging and allows visualisation of bone metabolism or bone remodeling, which most other imaging techniques (such as X-ray computed tomography, CT) cannot. Bone scintigraphy competes with positron emission tomography (PET) for imaging of abnormal metabolism in bones, but is considerably less expensive. Bone scintigraphy has higher sensitivity but lower specificity than CT or MRI for diagnosis of scaphoid fractures following negative plain radiography. The most common radiopharmaceutical for bone scintigraphy is 99mTc with methylene diphosphonate (MDP). Other bone radiopharmaceuticals include 99mTc with HDP, HMDP and DPD. MDP adsorbs onto the crystalline hydroxyapatite mineral of bone. Mineralisation occurs at osteoblasts, representing sites of bone growth, where MDP (and other diphosphates) "bind to the hydroxyapatite crystals in proportion to local blood flow and osteoblastic activity and are therefore markers of bone turnover and bone perfusion