TC-99M LABELED HUMAN SERUM-ALBUMIN FOR VENTRICULOGRAPHY - A COMPARATIVE-EVALUATION OF 6 LABELING KITS

In this study we have compared the characteristics of six labelling ki ts for the preparation of technetium-99m labelled human serum albumin (Tc-99m-HSA) and evaluated the usefulness of the various Tc-99m-HSA pr eparations as blood pool tracer agents. The amount of the principal in gredients, i.e. HSA and stannous ions, varies largely between the stud ied kits and this is probably a reason for the observed differences in the labelling rate. Analysis of the reaction mixtures after labelling of the respective kits with Tc-99m showed in each preparation the pre sence of four to five radioactive components in variable relative amou nts. The retention time of the main component on size-exclusion high-p erformance liquid chromatography (SEC-HPLC) was identical for all prep arations. Biodistribution of the HPLC-isolated fractions was studied i n mice. The components with the shortest and longest retention times o n HPLC show poor retention in the plasma. The three intermediate fract ions, including the principal peak, are initially retained relatively well in the blood (60%-70% of the injected dose after 10 min), but cle arly to a lower degree than iodine-125 labelled HSA. Moreover, they di ffuse out of the vascular compartment at a much higher rate than I-125 -HSA. The biological behaviour of the main component of the various pr eparations was clearly different, despite the identical retention time on SEC-HPLC. Study of the total preparations in mice and a rabbit sho wed that two of them are cleared rapidly from the blood and cannot be considered valuable blood pool tracers. Diffusion of the other prepara tions out of the blood is slower but also considerable and compromises their use for ventriculography.