Effect of temporal sampling on evaluation of left ventricular ejection fraction by means of thallium-201 gated SPET: comparison of 16-and 8-interval gating, with reference to equilibrium radionuclide angiography

Gated myocardial single-photon emission tomography (SPET) allows the evalua tion of left ventricular ejection fraction (LVEF), but temporal undersampli ng may lead to systolic truncation and ejection fraction underestimation. T he aim of this study was to evaluate the impact of temporal sampling on tha llium gated SPET LVEF measurements. Fifty-five consecutive patients (46 men , mean age 62+/-12 years) with a history of myocardial infarction (anterior 31, inferior 24) were studied. All patients underwent equilibrium radionuc lide angiography (ERNA) and gated SPET 4 h after a rest injection of 185 MB q (5 mCi) of thallium-201 using either 8-interval (group 1, n=25) or 16-int erval gating (group 2, n=30). In group 2, gated SPET acquisitions were auto matically resampled to an 8-interval data set. Projection data were reconst ructed using filtered back-projection (Butterworth filter, order 5, cut-off 0.20). LVEF was then calculated using commercially available software (QGS ). A higher correlation between gated SPET and ERNA was obtained with 16-in terval gating (r=0.94) compared with the resampled data set (r=0.84) and 8- interval gating (r=0.71). Bland-Altman plots showed a dramatic improvement in the agreement between gated SPET and ERNA with 16-interval gating (mean difference: -0.10%+/-5%). Using multiple ANOVA, temporal sampling was the o nly parameter to influence the difference between the two methods. When usi ng 8-interval gating, gated SPET LVEF was overestimated in women and undere stimated in men (ERNA minus gated SPET -4.0%+/-9.6% in women and 3.6%+/-7.6 % in men, P=0.01). In conclusion, 16-interval thallium gated SPET offered t he best correlation and agreement with ERNA, and should be preferred to 8-i nterval gated acquisition for LVEF measurement.