Nuclear medicine communications
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We report a study of the renal and whole-blood kinetics of (18)F-fluoride and (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) and their effect on the evaluation of the skeletal kinetics of the two bone tracers. Data were obtained during an investigation of postmenopausal women taking hormone replacement therapy who were compared with untreated, age-matched controls. After intravenous injection of 18F-fluoride (1 MBq), (99m)Tc-MDP (1 MBq), (51)Cr-ethylenediaminetetraacetic acid (51Cr-EDTA) (3 MBq) and (125)I-human serum albumin ((125)I-HSA) (0.25 MBq), multiple blood samples and urine collections were taken between 0 and 4 h after injection. (51)Cr-EDTA data were used to evaluate the glomerular filtration rate (GFR) and the completeness of each timed urine collection. (125)I-HSA data were used to evaluate the plasma volume and the red cell uptake of the other three tracers. ⋯ Between 0 and 4 h after injection, the fractional protein binding of MDP increased linearly with time, changing from 21+/-5% immediately after injection to 58+/-5% at 4 h. Although red cell uptake of (99m)Tc-MDP was negligible, for (18)F-fluoride around 30% of circulating tracer was transported in red cells. In view of the data showing the rapid transport of (18)F-fluoride across the red cell membrane, bone kinetic data for (18)F are more accurately reported as whole-blood clearance rather than plasma clearance.