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Myocardial Tracking, A New Method to Calculate Ejection Fraction with Gated SPECT: Validation with ²⁰¹Tl Versus Planar Angiography

Department of Nuclear Medicine, Henri Mondor Hospital, Paris XII University, Créteil; HealthCenter Internet Services, Sophia-Antipolis, France; and Department of Nuclear Medicine, Military Hospital of Tunis, Tunisia

Left ventricular ejection fraction (LVEF) and viability are essential variables for the prognosis of myocardial infarction and can be measured simultaneously by ²⁰¹Tl gated SPECT; however, most algorithms tend to underestimate LVEF. This study aimed to evaluate a new myocardial tracking algorithm, MyoTrack (MTK), for automatic LVEF calculation. Methods: A rest/redistribution (20 min/4 h) ²⁰¹Tl gated SPECT protocol followed immediately by a ^99mTc equilibrium radionuclide angiography (ERNA) was performed in 75 patients with history of myocardial infarction. Quality of myocardial uptake was evaluated from count statistics and automatic quantification of defect sizes and severities (CardioMatch). LVEFs were calculated both with Germano’s quantitative gated SPECT (QGS) algorithm and with MTK. Briefly, the originality of this algorithm resides in the unique end-diastole segmentation, matching to a template and motion field tracking throughout the cardiac cycle. Results: ERNA LVEF averaged 33% ± 14%. QGS significantly underestimated this value at 20 min (30% ± 13%, P < 0.001) and at 4 h (30% ± 13%, P < 0.0001). By contrast, MTK did not miscalculate LVEF at 20 min (34% ± 14%, probability value was not significant) though a similar underestimation occurred at 4 h (31% ± 13%, P < 0.02). Individual differences between early and late gated SPECT values and differences between gated SPECT and ERNA values did not correlate with the extension of perfusion defects, count statistics, or heart rate. Conclusion: The MTK algorithm calculates LVEF on early/high-count images more accurately than ERNA, even in patients with severe perfusion defects, but tends to underestimate LVEF on delayed/low-contrast images, as other algorithms do.

Key Words: ²⁰¹Tl • gated SPECT • ejection fraction • accuracy • precision