An automated software program (e-soft, 2.5, QGS/QPS, Cedars-Sinai Medical Center, Los Angeles, CA) was used to calculate the scores incorporating both the extent and severity of perfusion defects, using standardized segmentation of 17 myocardial regions [16]. The summed stress score (SSS), representing the total abnormal myocardium (i.e., necrotic and ischemic tissue), was obtained by adding the scores of the 17 segments of the stress images. A SSS > 3 was considered abnormal [17]. A similar procedure was applied to the resting images to calculate the summed rest score and the summed difference score. Total perfusion defect reflecting a combination of both severity and extent of myocardial defect was also calculated and categorized according to the presence of ≥ 10% of abnormal myocardium.