Evaluation of 99Tcm-bicisate as a renal imaging agent

Tc-bicisate (Tc-ECD), often used as a brain perfusion agent, is rapidly converted following intravenous injection to the polar monoacid (Tc-ECM) and diacid (Tc-EC) metabolites. Such polar metabolites, which are eliminated principally by renal clearance, are potential renal imaging agents. In this study, Tc-ECD was compared for the first time with Tc-EC, Tc-mercaptoacetyltriglycine (Tc-MAG3) and I-orthoiodohippurate (OIH) as renal imaging agents in rabbits. Whole-body images and renograms were obtained for all three of the Tc agents, and pharmacokinetic parameters including plasma and urinary clearance were studied for all four agents. The plasma clearance of Tc-EC (37 ml min) was slower than that of Tc-ECD (51 ml min), which could be accounted for by the higher liver uptake of Tc-ECD. The urinary clearance of Tc-ECD (35 ml min), Tc-EC (34 ml min) and Tc-MAG3 (39 ml min) was similar. The renal images obtained with Tc-ECD were comparable to those for Tc-MAG3 and Tc-EC. However, liver uptake was more prominent with Tc-ECD than with the other agents. The Tc-ECD renogram curves showed a prolonged decrease in renal activity compared to both Tc-EC and Tc-MAG3. In potential human studies, the relatively high liver uptake of Tc-ECD superimposed on right renal activity may be a limitation. Therefore, we conclude that Tc-ECD is less favourable when compared to existing renal agents due to its high extrarenal uptake and renal kinetics.