Relative distribution of diphosphonate between bone and soft tissue at 4 and 24 hours: concise communication.

Digital bone scintigrams were obtained in 19 patients using Tc-99m hydroxyethylidene diphosphonate (HEDP). These were quantitated for skeletal, soft-tissue and renal uptake of tracer using a contrast-enhancement technique to define the regions of interest. Twenty-four hr whole-body retention (WBR) of HEDP was also measured. It was found that approximately 70% of retained diphosphonate was localized in the skeleton at 24 hr, with 26% in soft tissue and 4% in kidneys. However, we have shown that over a wide spectrum of whole-body retention measurements (18 to 70%) the 24-hr soft-tissue component, as a percentage of administered dose, remained relatively constant whereas skeletal tracer accumulation mirrored WBR (r = 0.98, p less than 0.001). The present study indicates that, despite a significant but essentially stable soft-tissue component, measurement of 24-hr WBR of HEDP accurately reflects skeletal metabolism.