Abstract： Objective To compare radiation dose and image quality between prospective electrocardiograph(ECG)-triggered axial seau and retrospective ECG-gated helical scan in coronary 64-slice CT angiography(CTA).Methods Seventy-seven consecutive patients[group A.Average body mass index (BMI):24.6,heart rate＜70 bpm]underwent 64-slice CTA using prospective ECG-triggered axial scan protocol(120 kV,mA tailored to BMI).For each patient,the simulated radiation dose using retrospective ECG-gated scan protocol without ECG-driven X-ray current modulation technology was calculated and recorded at sanle kV and mA.Retrospective ECG-gated scan protocol was performed on 30 consecutive patients in another group(group B.Average BMI:23.9,heart rate＜70 bpm).The image quality was blindly evaluated between group A and B(paired t-test was used and P＜0.05 as a significant difference).Results There Was a significant difference(t=18.50,P＜0.01)between radiation dose of group A (3.37 mSv)and that of group B(18.13 mSv),decreased by 81.4%.The image quality of group A could fulfill clinical diagnostic needs.The average radiation dose of using simulated helical scan without optimization was 17.29 mSv,which wag similar to that of group B(18.13 mSv)(t=0.87,P＞0.05).Condusion Prospective ECG-triggered axial scan in 64-slice coronary CTA Call significantly reduce radiation exposure and the image quality can fulfill clinical diagnostic needs.