Objective To compare the low- and standard-dose protocols in the evaluation of coronary artery calcification (CAC) scores and in image quality,and to assess the accuracy of low-dose prospective ECG-gated helical CT in CAC measurements.Methods Forty-three patients with CAC were scanned twice using a tube current setting of 100 and 55 mA retrospectively.CAC scores (Agatston) of different branches of coronary artery were recorded.The mean and SD of the CT attenuation values in regions of interest in the aorta were measured,and the value (mean + 2 × SD) were obtained.Results Calcification plaques were found in 105 of the 172 vessels in the 43 subjects.The radiation dose of the 50 mAs group was (0.72 ± 0.04) mSy,significantly lower by 0.6 mSv than that of the 100 mAs group [(1.32 ± 0.08) mSv,P ＜ 0.05].The total calcification score of the 55 mAs group was significantly positively correlated with the routine dose group after performing the square root transformation (r =0.998).A signficant correlation existed in vessel-based calcification between these 2 groups (r= 0.997).Conclusions Low-dose prospective ECG-gated 64-slice CT yields high accuracy on CAC scoring while maintaining the image quality needed to measure CAC.