Technetium-99m DTPA uptake and transit in bone: effect on blood clearance in rabbits

The purpose of this study is to explain the initial "plateau" distribution of [99mTc]DTPA in the forearm found when using serial external counting for kidney clearance measurements. A study by a MIRD task group, McAfee et al. 1979 (1), measured the biologic distribution of [99mTc]DTPA(Sn) in most body tissues but omitted bone, which we believe is a major contributor to this initial "plateau". Using MIRD criteria, measurements were carried out on rabbit humeri and these were compared with results obtained from human subjects. It would appear that initial accumulation of the compound by interstitial bone is the reason for the "plateau" and explains why blood sampling for GFR studies should not be undertaken over the first 2 hr. In addition, the results of this study provide valuable information relevant to bone perfusion studies and the biologic distribution and concentration of i.v. administered drugs during the first 2 hr postinjection.