Influence of the radioactive concentration of the in vitro stability of Tc-99m(Sn)-pyrophosphate
The in vitro stability of Tc-99m(Sn)-pyrophosphate solution was examined in dependence on the preparation conditions of the samples, the radioactive concentration of Tc-99m in the kit and the time elapsed after labeling. The samples without any protection are highly unstable. The formation of Tc-99m-pertechnetate does not depend on the radioactive concentration. Nitrogen purging provides protection in the case of low radioactive concentrations (37 MBq Tc-99m/ml) but exhibits no effect at higher concentrations. The best stabilization was achieved by using ascorbic acid. A concentration of 60 mu g/ml keeps the content of Tc-99m-pertechnetate below 1% during six hours after labeling, even in solutions of high radioactive concentrations (740-814 MBq/ml). Gentisic acid is less effective. Concentrations about ten times higher than required using ascorbic acid are needed to keep the content of Tc-99m-pertechnetate below 5% during six hours.