Effect of attenuation correction on wall motion quantification in Tl-201 ECG-gated myocardial SPECT

Abstract

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Objectives: Influence of attenuation correction (AC) on Quantitative Gated SPECT (QGS) has not been clarified yet. The purpose of this study was to estimate the effect of AC on wall motion (WM) measurement of QGS. Methods: The normal group consisted of 13 subjects (age 68±10 yrs) in whom ischemic heart disease (IHD) was ruled out by ultrasonography, angiography, and/or clinical courses. IHD pts with history of myocardial infarction were divided on the basis of coronary angiography into groups of LAD: 6 pts, LCX: 2 pts, RCA: 7 pts. ECG gated SPECT was obtained at 10 min (early) and 3 hr (delayed) after exercise and injection of 74 MBq of Tl-201. Data were acquired using a 2-head gamma camera (FORTE, ADAC, CA, USA) with 180 degrees arc, 60 sec × 32 projections, 64×64 matrix with 8 frames per R-R interval. Transmission data was obtained using the system Vantage equipped with gadolinium-153 scanning line sources. The original software for AC was improved so that both emission and transmission data could be reconstructed for gating. Gated images without and with AC were then analyzed by QGS. Results: In normal subjects, AC-to-non AC ratio of accumulated counts was 1.12, 1.14, 1.15, 1.23, 1.03 for the apex, anterior, septum, inferior, lateral, respectively. In WM measurement for normal subjects, WM (mm) with AC was significantly larger than that without AC: septum 6.1±1.3 with AC vs 5.5±1.6 without AC (P=0.003) at early, and septum 6.2±2.5 vs 5.5±1.8 (P=0.05), inferior 7.8±1.9 vs 7.0±1.4 (P=0.04) at delayed. In IHD group, myocardial segments having higher viability showed significantly larger WM values when applied to AC. Such increased WM in AC was not observed in non-viable myocardium. Thus, WM measurement with AC contrasted the difference in WM between viable and non-viable myocardium. Conclusions: Application of AC raised WM values in normal myocardium and slightly ischemic myocardium, but not in non-viable myocardium. AC is useful for detection of WM abnormality in non-viable myocardium by enhancing magnitude of WM decrease in comparison with viable myocardium.