Objective To explore the application of high-pitch late artery scanning by dual-source CT in evaluating the filling defect and morphological measurement of left atrial appendage(LAA).Methods A total of 80 patients requiring LAA CT angiography(CTA)scanning due to atrial fibrillation(AF)admitted in our hospital from July to October 2022 were enrolled,and their clinical data were collected.The second-generation dual-source CT high-pitch FLASH scanning was adopted to all the patients who were randomly divided into group A(arterial phase scanning,40 cases)and group(late arterial phase scanning B,40 cases).All patients underwent dual-phase scanning and the time interval was 30 s.According to the filling defects of LAA in the first phase,the patients were divided into LAA filling group(n=59)and non-filling group(n=21).The radi-ation dose the patients received was recorded.The CT values of LAA,ascending aorta(AA)at the same slice and left atrium(LA)at its largest slice were calculated,and the short diameter,long di-ameter,area of LAA opening and depth of LAA were also measured.Results The radiation dose received in patients in phase 1 was 2.2(2.0,3.9)mSv,and that in phase 1+delayed was 2.7(2.4,4.8)mSv,with significant difference between the first and the first+delayed scanning period(P＜0.01).The ratios of CT values(LAAHU/AAHU and LAAHU/LAHU)and of LAA filling defect in the first phase were significantly higher in the group B than the group A(P＜0.05,P＜0.01).The long diameter,short diameter,area of LAA opening and depth of LAA were obviously lower in the LAA filling group than the non-filling group(26.6±3.1 mm vs 30.1±2.8 mm,P＜0.01;20.8±2.9 mm vs 22.8±2.1 mm,P＜0.01;454.6±92.1 mm2 vs 561.9±85.9 mm2,P＜0.01;35.8±4.8 mm vs 40.7±5.4 mm,P＜0.01).Conclusion High-pitch Flash late arterial phase scanning by dual source CT can significantly elevate the LAA filling defects,shorten the examination time and reduce the radiation dose in patients.It is worthy of clinical application and promotion.