99mTc-MDP accumulation mechanisms in bone: Basic study on the adsorption onto hydroxyapatite

The accumulation mechanisms of technetium-99m methylene diphosphonate (99mTc-MDP) were investigated using hydroxyapatite powder and various phosphates. After reaction with99mTc-MDP, radioactivity was analyzed using a scintillation counter. The adsorption of99mTc-MDP onto hydroxyapatite occurred within 30 sec, and was not temperature dependent at 0–95°C. There was no change in the adsorption of99mTc-MDP onto hydroxyapatite in 5 or 50mM water-soluble organic compounds (glucose or urea). Anions had a greater effect on adsorption than cations. The only phosphate with adsorption equal to that of hydroxyapatite was calcium pyrophosphate. Adsorption onto calcium hydrogenphosphate was low at a pH of 6.0 in comparison with hydroxyapatite. These findings suggest that the adsorption of99mTc-MDP onto hydroxyapatite is influenced by the concentration of coexisting anions and by the chemical constitution of the phosphate components.