CARDIAC STRESS-REST SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY WITH TECHNETIUM 99M-LABELED TETROFOSMIN - INFLUENCE OF WASHOUT KINETICS ON REGIONAL MYOCARDIAL UPTAKE VALUES OF THE REST STUDY WITH A 1-DAY PROTOCOL

Background. The purpose of this study was to evaluate (1) the washout kinetics of Tc-99m-labeled tetrofosmin, separately for myocardium with normal and reduced perfusion, and (2) its influence on quantitative a nalysis in a 1-day stress-rest protocol. Methods and Results. Twenty-f ive patients with angiographically proved coronary artery disease unde r-went bicycle exercise stress testing with injection of 200 MBq Tc-99 m-labeled tetrofosmin and first single-photon emission computed tomogr aphic (SPECT) imaging 40 minutes after injection, A second SPECT was a cquired 2.3 +/- 0.4 hours after the first one immediately before rest injection of 800 MBq Tc-99m-labeled tetrofosmin, The rest (third) SPEC T was acquired 15 minutes thereafter, The relative washout fraction pe r time (WOFt) was calculated assuming linear washout kinetics, Thirty- three regional uptake values per study were calculated, normalized to the perfusion maximum (100%) in either the postexercise SPECT and the rest SPECT, for the latter with and without correction of remaining co unts from stress injection, In regions with normal perfusion, WOFt was 11.5% +/- 3.5% per hour, In regions with markedly reduced perfusion ( relative uptake <50%, WOFt was 8.3% +/- 9.9% per hour, The highest var iation of the relative uptake values between rest SPECT with and witho ut correction of remaining counts from stress injection was 5.4% +/- 3 .5% in regions with stress-induced ischemia. Conclusion. To use a 1-da y protocol with a stress-rest radioactivity ratio of 1:4 and an interv al of more than 2 hours between the examinations, a correction for rem aining counts from stress injection seems not to be necessary for the quantitative analysis of rest SPECT.