Attenuation correction improves the detection of viable myocardium by thallium-201 cardiac tomography in patients with previous myocardial infarctionand left ventricular dysfunction

The aim of this study was to determine the influence of attenuation-correct ed thallium-201 stress/redistribution/reinjection single-photon emission to mography (SPET) on the number of viable segments in patients with previous myocardial infarction and dysfunctional myocardium. Fifty-one patients with previous myocardial infarction and left ventricular dysfunction were inclu ded in the study. In all patients, Tl-201 non-corrected (NC) and attenuatio n-corrected (AC) SPET was performed using a stress/redistribution/reinjecti on protocol followed by coronary angiography, A semiquantitative analysis w as performed using polar maps for NC and AC stress, redistribution and rein jection short-axis and vertical long-axis (apex) slices. Severe (perfusion defect below 50%/maximal count rate: PD<50), mild and moderate persistent d efects for redistribution and reinjection were evaluated for both NC and AC studies. A total of 1581 segments were evaluated by semiquantitative segme ntal analysis for both NC and AC studies for each redistribution and reinje ction map. In the redistribution maps, NC revealed a total of 352 segments and AC a total of 222 segments with impaired perfusion below 50% of the max imal count rate (PD<50). The mean number of affected segments was 6.9 +/- 5 .5 in the case of NC and 4.4 +/- 4.8 in the case of AC (P < 0.001), In the reinjection maps, NC revealed a total of 263 non-viable segments (PD<50) an d AC a total of 169 non-viable segments. The mean number of affected segmen ts was 5.2 +/- 5.3 in the case of NC and 3.3 +/- 4.2 in the case of AC (P < 0.001), Recovery of function was better predicted by AC than by NC in 20% of patients in the follow-up group. Therefore, the use of attenuation corre ction influences the extent of viable segments by showing more viable segme nts in either redistribution or reinjection maps. Tl-201 imaging without at tenuation correction may underestimate the extent of tissue viability, whic h may contribute to the lower sensitivity compared to fluorine-18-fluorodeo xyglucose positron emission tomography, where attenuation correction is a r outinely performed procedure.