No abstract

The residue and extraction of technetium-labelled methylene diphosphonate (99mTc-MDP), a substance used in bone scanning, was examined in the canine tibia and found to be low. Examination of washout curves suggested that there were four compartments in cortical bone, a vascular, a perivascular, a bone fluid and a bone compartment. After an osteotomy in the canine tibia the residue of 99mTc-MDP increased. This was believed to be due to an increase in the blood supply to the bone and to an associated increase in new bone available for exchange. Bone scanning in a fracture is therefore a reflection of the vascular status of the bone being examined and of the uptake by bone. This is dependent on there being an adequate blood supply to the bone and an increased number of mineral-binding sites.

A technique is described which will allow a study of the microcirculation to a long bone such as the femur. It involves use of a silicone rubber compound (Microfil) in combination with the Spalteholz clearing technique. Preliminary results in the normal rabbit skeleton suggest that this technique can be used to study the changes in vascularity which occur under various pathological conditions.

Summary A method is described for the preparation of a freeze‐dried stannous methylene diphosphonate kit* (Sn‐MDP) suitable for use in bone scanning after complexing with 99mTc. Several combinations of the reagents were used, and these resulted in different levels of bone and soft tissue localization. Two of such combinations produced a kit which localized predominantly in bone, and of these only one showed consistent batch to batch reproducibility. The biological distribution of the labelled compound has been tested in animals, and the results obtained at 2 h post‐injection are presented. The shelf‐life has been found to be in excess of 3 months, and quality control using thin layer chromatography has shown a labelling yield >95%.

An experimental technique is described to measure the accumulation of 99Tcm-stannous-ethane-1-hydroxy-1, 1-diphosphonate (99Tcm-EHDP) in the canine tibia. The method involves infusion at a constant rate of known amounts of 99Tcm-EHDP into the nutrient artery supplying the tibial bone. The accumulation of the diphosphonate in bone is measured by an external sodium iodide, Nal (T1), scintillation detector. Results are presented showing that for small amounts of 99Tcm-EHDP (0.004-0.300 mg per hour) the accumulation is a nearly linear function with time for 60 minutes, after which the uptake may become variable with either a plateau formation or considerable fluctuation of activity.