Mechanism of accumulation of 99mTc-MDP to bone: correlation of in vivo data with in vitro data.

The uptake of 99mTc-methylene diphosphonate (99mTc-MDP) to bone was studied in two types of bone diseases using the tibial bone of rats. One was a planned, specific bone injury, and the other was an osteomyelitis model. Both models were evaluated with scintigraphy (for scintigram and uptake ratio) and 31P-magnetic resonance spectroscopy [for pH, mineral (inorganic) phosphate to creatine phosphate (Pi/PCr) ratio and ATP/PCr ratio] over a period of three weeks. Results in the scintigram of the injured bone model demonstrated a distinct uptake spot, while that in the scintigram of the osteomyelitis model showed a diffuse uptake. The scintigraphy demonstrated an increase in the 99mTc-MDP uptake ratio in the both models with a peak approximately one week after treatment, after which the uptake ratio gradually decreased. The uptake ratio of the injured bone model was greater than that of the osteomyelitis model. There was no significant change in pH, Pi/PCr or ATP/PCr in the injured bone model during that period. There was a significant change in pH and ATP/PCr, but not in Pi/PCr, in the osteomyelitis model during that period. Further, in the osteomyelitis model, an increased 99mTc-MDP uptake ratio reach a peak at about one week, while the pH and the ATP/PCr were at their lowest values at about two weeks. These results suggest that the accumulation of 99mTc-MDP to the bone will be affected by the type of disease or environmental factors such as pH and concentration of phosphates.