Radioimaging of implants in rats using Tc-99m-MDP

Radiopharmaceutical isotopes are widely used clinically to detect tumors of osteogenic origin. One example is Technetium-99m methylene diphosphonate ( Tc-99m-MDP). When viewed with a gamma camera, the concentration of the isot ope (increased gamma activity) indicates an area of increased bone activity . This technology provides an opportunity to measure bone growth around imp lants in vivo. The purpose of this study was to measure Tc-99m-MDP activity around titanium alloy implants placed in the tibiae of rats. Some implant sites were treated with a growth factor; other sites served as controls. Th e hypothesis tested was that implants placed with a growth factor would hav e greater associated Tc-99m-MDP activity. Twelve adult mate Sprague-Dawley rats were anesthetized and surgical access to the medial proximal tibiae wa s obtained. Titanium alloy screw implants were placed in six animals along with 65 mug of acidic fibroblast growth factor (FGF-I); the other six anima ls received implants only and served as controls. After five days, rats wer e injected with 1500 mu Ci of Tc-99m-MDP After 3 hours, rats were imaged wi th a gamma camera. The Tc-99m-MDP intensity associated with each implant wa s quantified and the means for each group were compared using ANOVA. Implan ts treated with FGF-1 demonstrated significantly more Tc-99m-MDP activity t han implants alone. This suggests that Tc-99m-MDP analysis may be a useful tool for determining bone growth around implants in laboratory animals in v ivo.