In vivo chemistry of 99mTc-chelates

The structure-activity relationships involved in the in vivo localization and clearance of 99mTc-chelates is reviewed. Most 99mTc-chelates used for renal studies are mixed function agents and their uptake in the kidney is affected by the presence or absence of stannous ions; only a relatively few chelates are almost exclusively cleared from the body by glomerular filtration or tubular excretion. The uptake of 99mTc-phosphates and -phosphonates in metabolically active and metabolically inactive bone and the plasma clearance rate of these complexes depend upon the structure of the complexing ligand. 99mTc-chelates considered optimal for hepatobiliary imaging have a high liver extraction efficiency, are rapidly transported through the liver and have a comparatively slow renal clearance rate. Even though the elucidation of the in vivo behavior of 99mTc-chelates continues, quantitating structure-activity relationships requires that the structure of the chelates be carefully characterized, both before and after injection.