Accumulation of technetium-99m methylene diphosphonate. Conditions affecting adsorption to hydroxyapatite

Experiments were carried out to explore the mechanism of technetium-99m methylene diphosphonate (99mTc-MDP) adsorption with various calcium compounds including hydroxyapatite powder. 99mTc-MDP adsorption to hydroxyapatite was markedly inhibited by the addition of either pyrophosphate or methylene diphosphonate (MDP). Moreover, adsorbed 99mTc-MDP was partly removed by rinsing with pyrophosphate solution. Adsorption was pH-dependent and was inhibited by univalent cations, adenosine triphosphate solution, and guanosine triphosphate. Adsorption was most apparent to hydroxyapatite and calcium pyrophosphate and was less marked for the other calcium compounds tested. It is suggested that 99mTc-MDP adsorption is affected by the hydroxyapatite crystalline structure and environmental factors such as pH and the presence of phosphates, calcium compounds, and various cations.