The most common radiopharmaceutical for bone scintigraphy is 99mTc with methylene diphosphonate (MDP).[12] Other bone radiopharmaceuticals include 99mTc with HDP, HMDP and DPD.[13][14] MDP adsorbs onto the crystalline hydroxyapatite mineral of bone.[15] 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".[16][17]