Preparation and Biodistribution of ⁹⁹Tc^m-DTPA-Gd

To observe the biologic characteristics of Gd-DTPA labeled with ⁹⁹Tc^m , the labeled compounds were prepared by reducing ⁹⁹Tc^m in the presence of Gd-DTPA with stannous chloride. The labeling efficiency was measured by TLC（>98%, and stable at room temperature within 6 h）. The plasma protein binding rate measured by the trichloroacetic acid method is (3.80±0.25)%. The bio-distribution in mice was observed by the blood sampling and other major organs that were taken out from mice at 1, 5, 10, 15, 30, and 60 min after intravenous injection of labeled compounds. The percentage of the injected dose per gram of tissues（%ID/g) of the blood and kidney are the highest level at 1 min after injection of ⁹⁹Tc^m-DTPA-Gd. They are （14.79±9.77）%ID/g and （26.02±8.50）%ID/g, respectively. Heart, liver, spleen and lung have a little distribution of radiopharmaceuticals, and brain has the lowest level uptake less than 1%. The deposition of ⁹⁹Tc^m-DTPA-Gd in other major organs was less than 1% at 30-60min after injection. Renal dynamic scintigraphy in rabbits are administrated, and show that ⁹⁹Tc^m-DTPA-Gd is quickly excreted by kidney, and the time to peak is about 5-10 min, the half time of clearance is about 10-20 min. The animal experiments in vivo and in vitro show that ⁹⁹Tc^m-DTPA-Gd and ⁹⁹Tc^m-DTPA have the qualitatively similar biodistribution and excretion. ⁹⁹Tc^m labeled Gd-DTPA may be a significant way not only to study its bio-distribution but also to directly observe its distribution and excretion by renal dynamic scintigraphy.