Reproducibility and accuracy of gated SPECT for determination of left ventricular volumes and ejection fraction: Experimental validation using MRI

Quantitative gated SPECT (QGS) has been used for computation of left ventri cular volumes and ejection fraction. This study evaluated, first, the effec t of injected dose, time of imaging, and background activity on the reprodu cibility of QGS and, second, the accuracy of QGS, compared with cine MRI, f or determining left ventricular volumes and ejection fractions in dogs with and without perfusion defects. Methods: Sixteen dogs were subjected to eit her chronic occlusion of the circumflex artery (group I, no perfusion defec t) or acute occlusion of the anterior descending coronary artery (group II, perfusion defect). Both groups underwent serial MRI and SPECT. Results: QG S was very reproducible using the automated program (r = 0.99997). Correlat ion between left ventricular ejection fraction (LVEF) at 15 and 45 min was poor after the low-dose injection (r = 0.54; SE = 9%) and only fair after t he high-dose injection (r = 0.77; SE = 5%). Correlation was poor in the pre sence of significant background activity (r = 0.36; SE = 12%), Correlation between QGS left ventricular volumes and MRI was good for group I (end-dias tolic volume, r = 0.86; end-systolic volume, r = 0.81) and only fair for gr oup II (end-diastolic volume, r = 0.66; end-systolic volume, r = 0.69). The overall LVEF correlation between QGS and MRI was poor (r = 0.51). QGS LVEF (mean +/- SD, 42% +/-: 3%) overestimated MRI LVEF (29% +/- 2%). Conclusion : QGS provides a highly reproducible estimate of LVEF, However, QGS is affe cted by changes in background activity, time of imaging, and injected dose. In the presence of perfusion defects, QGS overestimated volume relative to MRI. The correlation between QGS- and MRI-derived LVEF was poor in this ca nine model.