Assessment of ejection fraction with Tl-201 gated SPECT in myocardial infarction: Precision in a rest-redistribution study and accuracy versus planarangiography

Background. Viability and left ventricular ejection fraction (LVEF) are ess ential measures for the assessment of myocardial infarction (MI). These 2 v ariables may be evaluated simultaneously by means of thallium-201 gated sin gle photon emission computed tomography (SPECT); however, the precision and accuracy of LVEF measurements with this isotope remain controversial, part icularly in cases of extended perfusion defects and poor count densities. Methods and Results. Fifty patients with a history of MI underwent a 20-min ute rest and a 4-hour redistribution T1-201 gated SPECT viability protocol, immediately followed by a technetium-99m planar equilibrium radionuclide a ngiography (ERNA). On gated SPECT images, various count statistics were cal culated, and perfusion was automatically quantified by means of CardioMatch , which provided both the size and severity of MI defects. Rest and redistr ibution LVEFs were determined from gated SPECT with Germane's algorithm, wh ereas LVEFs were calculated from ERNA using the manufacturer's software. Me an LVEF values calculated with rest gated SPECT, redistribution gated SPECT , and planar ERNA were 30% +/- 13%, 30% +/- 13% and 33% +/- 13%, respective ly. Significant differences between repeated gated SPECT LVEFs were not sho wn by means of the paired t test. Correlation coefficients were high betwee n 20-minute and 4-hour scans (r = 0.89) and between gated SPECT and ERNA (r = 0.88 and r = 0.92 at 20 minutes and 4 hours, respectively). Additionally , close agreement between gated SPECT and ERNA was shown by means of the Bl and-Altman plot, despite an underestimation of 3 units. Finally, neither th e technical conditions (count density, heart rate, lung uptake, etc) nor th e perfusion alteration (size, severity, redistribution) appeared to interfe re with the precision and accuracy of gated SPECT LVEF measurement. Conclusion. T1-201 gated SPECT is a precise method for assessing LVEF withi n the same patient at 4-hour intervals, even with a substantial count decay , and it gives accurate results compared with planar ERNA, even in the case of large perfusion defects.