COMPARISON OF MODIFIED TC-99M ALBUMIN AND TC-99M RED-BLOOD-CELLS FOR EQUILIBRIUM VENTRICULOGRAPHY

A newly developed modified form of Tc-99m-labeled human serum albumin reconstituted from a kit (Tc-99m-dimercaptopropionyl-human serum album in; Tc-99m-DMP-HSA) was prospectively compared to Tc-99m-labeled red b lood cells (RBC) in patients referred for equilibrium radionuclide ven triculography at rest to evaluate its potential use as a blood-pool im aging agent. Methods: A Paired comparison between Tc-99m-DMP-HSA and e ither in vitro or in vivo Tc-99m-labeled RBC was performed within 2 da ys in 20 patients. For each study, two sets of images were acquired, s tarting at 15 min and 180 min postinjection, respectively, Each set co nsisted of a gated blood-pool cardiac study and a planar static image centered on the patient's thorax, All data were processed by two indep endent observers, Early and late postinjection parameters were calcula ted: ejection fraction (EF) value, activity within the main organs sur rounding the left ventricle (LV), ratio of activity between the LV and these surrounding organs for each study separately, and temporal (lat e/early) evolution of the intraorgan activities and of the LV/organ ra tios after decay correction. Results: The images and the visual wall-m otion analysis were of good quality with both agents in most patients, without significant image degradation at 180 min postinjection. Calcu lated EF values were highly comparable with the two tracers. Interobse rver variability was 0.17% (RBC) and 1.08% (DMP-HSA) for the early EF value (EF1), and 0.62% (RBC) and 0.27% (DMP-HSA) for the late EF (EF2) , Mean difference between EF2 and EF1 was 0.74% (Observer 1) and 0.28% (Observer 2) for Tc-99m-RBC, and -2.88% (Observer 1) and -2.07% (Obse rver 2) for Tc-99m-DMP-HSA. When comparing Tc-99m-DMP-HSA to Tc-99m-RB C the mean difference was 1.27% (Observer 1) and 0.36% (Observer 2) fo r EF1, and -2.35% (Observer 1) and -1.99% (Observer 2) for EF2. Also, the biodistribution and temporal evolution of the organ repartition of both compounds were stable and similar, with values of late/early act ivity ratios very close to one for all the studied organs [mean intrao rgan ratio: 0.946 for Tc-99m-RBC (range: 0.881-1.086) and 0.979 for Tc -99m-DMP-HSA (range: 0.914-1.141); mean late/early LV/organ ratio: 0.9 64 for Tc-99m-RBC (range: 0.919-1.016) and 0.967 for Tc-99m-DMP-HSA (r ange: 0.912-1.035)]. Conclusion: Paired comparison of kit-prepared Tc- 99m-DMP-HSA to Tc-99m-labeled RBC demonstrated that both agents were v ery closely related regarding as well the calculated EF value as the i n vivo stability up to more than 3 hr postinjection. Technetium-99m-DM P-HSA may constitute a practical and useful replacement for Tc-99m-lab eled RBC.