A newly developed modified form of 99mTc-labeled human serum albumin reconstituted from a kit (99mTc-dimercaptopropionyl-human serum albumin; 99mTc-DMP-HSA) was prospectively compared to 99mTc-labeled red blood cells (RBC) in patients referred for equilibrium radionuclide ventriculography at rest to evaluate its potential use as a blood-pool imaging agent.
Methods: A Paired comparison between 99mTc-DMP-HSA and either in vitro or in vivo 99mTc-labeled RBC was performed within 2 days in 20 patients'. For each study, two sets of images were acquired, starting at 15 min and 180 min postinjection, respectively. Each set consisted of a gated blood-pool cardiac study and a planar static image centered on the patient's thorax. All data were processed by two independent observers. Early and late postinjection parameters were calculated: ejection fraction (EF) value, activity within the main organs surrounding the left ventricle (LV), ratio of activity between the LV and these surrounding organs for each study separately, and temporal (late/early) evolution of the intraorgan activities and of the LV/organ ratios after decay correction.
Results: The images and the visual wall-motion analysis were of good quality with both agents in most patients, without significant image degradation at 180 min postinjection. Calculated EF values were highly comparable with the two tracers. Interobserver 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 99mTc-RBC, and -2.88% (Observer 1) and -2.07% (Observer 2) for 99mTc-DMP-HSA. When comparing 99mTc-DMP-HSA to 99mTc-RBC the mean difference was 1.27% (Observer 1) and 0.36% (Observer 2) for 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 activity ratios very close to one for all the studied organs [mean intraorgan ratio: 0.946 for 99mTc-RBC (range: 0.881-1.086) and 0.979 for 99mTc-DMP-HSA (range: 0.914-1.141); mean late/early LV/organ ratio: 0.964 for 99mTc-RBC (range: 0.919-1.016) and 0.967 for 99mTc-DMP-HSA (range: 0.912-1.035)].
Conclusion: Paired comparison of kit-prepared 99mTc-DMP-HSA to 99mTc-labeled RBC demonstrated that both agents were very closely related regarding as well the calculated EF value as the in vivo stability up to more than 3 hr postinjection. Technetium-99m-DMP-HSA may constitute a practical and useful replacement for 99mTc-labeled RBC.