Abstract： Objective:To explore the significance of four-dimensional CT angiography(4D CTA) and CT perfusion (CTP) imaging in evaluating collateral circulation grades in patients with moyamoya disease and moyamoya syndrome and their relationship with cerebral hemodynamics.Methods:The clinical and imaging data of 32 patients with moyamoya disease and moyamoya syndrome in Beijing Hospital from January 2017 to January 2022 were retrospectively analyzed. All patients underwent 4D CTA-CTP imaging. Collateral circulation was scored on CTA images by using Alberta stroke program early CT score system, and on digital subtraction angiography (DSA) images by using American society of interventional and therapeutic neuroradiology/Society of interventional radiology score system, respectively. The patients were divided into Ⅰ-Ⅲ circulation compensation grades based on collateral circulation score. Regions of interest were delineated at basal ganglia on perfusion maps and the perfusion parameters were obtained including cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), mean transit time (TTP) and delay time (DLY). The Kruskal-Wallis test was used to compare the perfusion parameters in different collateral circulation grades, and pairwise comparison was performed with Bonferroni correction. Kappa and Spearman tests were used to analyze the consistency and correlation of 4D CTA and DSA in the classification of collateral circulation.Results:4D CTA and DSA had a moderate consistency (Kappa=0.693, P<0.001) and a strong correlation ( r=0.805, P<0.001) in evaluating collateral grades. There were statistically significant differences in CBF, MTT and TTP among collateral compensation grade Ⅰ, grade Ⅱ and grade Ⅲ ( H values were 7.91, 11.69, 8.93; P values were 0.019, 0.003 and 0.012, respectively). Further pairwise comparison showed that the CBF of collateral compensation grade Ⅰ was lower than that of grade Ⅲ ( P=0.015), MTT of grade Ⅱ was higher than that of grade Ⅲ ( P=0.005), and TTP of grade Ⅰ was higher than that of grade Ⅲ ( P=0.015). There was no statistical significance of other indicators in pairwise comparison. There were no significant differences in CBV and DLY among collateral compensation grade Ⅰ, grade Ⅱ and grade Ⅲ ( P>0.05). Conclusions:4D CTA-CTP is equivalent to DSA in evaluating collateral circulation in patients with moyamoya disease and moyamoya syndrome. It can also evaluate the cerebral hemodynamics comprehensively, which has high clinical significance for disease monitoring.