Skeletal uptake of pyrophosphate labeled with technetium-95m and technetium-96, as evaluated by autoradiography.

For animal experimentation, the 95m and 96 technetium isotopes offer many advantages over technetium-99m. Their long physical half-lives and the emission of extranuclear electrons of low penetrating power make it possible to obtain autoradiograms of a great precision. The uptake of technetium stannous pyrophosphate by the epiphyseal plate was studied using liquid-emulsion microautoradiography, 3 hr after i.v. injection into 10-week-old rabbits. Microautoradiograms showed a well-defined and rather specific pattern of localization with intense uptake beneath the epiphyseal disk on the extremities of the vascular buds and a lack of accumulation in the cartilage, whether calcified or uncalcified. In the metaphysis, the label was located where new bone was being laid down and also over the cytoplasm of osteoclasts. We deduce from these results that in normal bone the general distribution of this tracer reflects mainly the arrangement of the blood supply, but the specific sites of accumulation are the bone-forming surfaces and the active resorbing osteoclasts.