Objective:To investigate the predictive value for major adverse cardiovascular events (MACE) occurring within 1 year in patients with old myocardial infarction(OMI) using characteristics of myocardial scar derive from dual-energy CT (DECT) post-processing technique.Methods:OMI patients who received coronary CT angiography following dual-energy CT with late iodine enhancement (LIE-DECT) in the Second Affiliated Hospital of Nantong University from November 2019 to October 2022 were continuously included, and the images of all enrolled patients were reconstructed using 40 keV monoenergetic plus (Mono+) map, LIE (representing myocardial scar) was quantified on left ventricular short-axis images, including the LIE segments, the LIE score, and the LIE degree. All enrolled patients were followed up for MACE, defined as hospitalization for heart failure, malignant arrhythmia, and cardiac death. Regression analysis was used to investigate the relationship between the quantified value of myocardial scar and the occurrence of MACE, and receiver operating characteristic curve (ROC) was used to evaluate the efficacy of quantified value of myocardial scar in predicting MACE. The area under the curve (AUC) was compared using the DeLong test.Results:Finally, 231 patients with OMI were included, and MACE occurred in 37 cases (16.0%) within 1 year after LIE-DECT examination. The LIE segments 5 (4, 7), the LIE score 27 (13, 49) and the LIE degree 9.4%(7.5%, 15.5%) in the MACE group were higher than those in the non-MACE group 3 (2, 5), 9 (6, 15) and 6.7%(6.3%, 7.9%) (all P<0.001). Multivariable logistic regression analysis showed that after adjusting for confounders, the LIE segments ( OR=2.118, P<0.001), the LIE score ( OR=3.168, P<0.001), and the LIE degree ( OR=3.092, P<0.001) remained risk factors for the development of MACE. On ROC analysis, AUC of LIE segments, LIE score and LIE degree were 0.715, 0.822 and 0.806 (all P<0.001), with sensitivities of 81.1%, 86.5%, and 91.9%, and specificities of 53.6%, 69.6%, and 60.8%, respectively. DeLong′s test showed that the predictive efficacy of LIE score and LIE degree was higher than that of LIE segments ( Z=2.63, P=0.008; Z=1.96, P=0.049), and there were no significant differences in the predictive efficacy of LIE score and LIE degree ( Z=0.60, P=0.551). Conclusion:The LIE segments, the LIE score and the LIE degree detected by LIE-DECT 40 keV Mono+maps are risk factors for the occurrence of MACE in patients with OMI and have good efficacy in predicting the occurrence of MACE, which can be used as important indicators for assessing the clinical prognosis of OMI.