Abstract: Objective: To optimize the scan protocol,and reduce the radiation dose in coronary angiography with 64-MSCT.Methods: 60 patients were randomly divided into two groups,30 included in each group.Calcium score images were scanned by tube current of 430 mA and 80 mA;delayed time was detected by timing bolus and Smart Prep,respectively;Coronary angiography was performed using ECG-gated protocol without tube current modulation and that with tube current modulation.In all groups,the mean effective dose and signal noise of ratio were calculated and compared.Results: Mean ED of calcium score scan obviously decreased from 2.35 ±0.42 of 430 mA to 0.42 ±0.03 of 80 mA;that of the delayed time detection reduce increasingly from 1.39 ±0.14 by timing bolus to 0.13 ±0.04 by Smart Prep;and that of coronary angiography protocol reduced from 28.22 ±4.90 without tube current modulation to 21.14 ±1.54 with tube current modulation.There were significant differences between mean SNR by 430 mA with that by 80 mA in calcium score scans,but there were no significant differences between mean SNR without tube current modulation with that with tube current modulation.Conclusion: Using the scan protocol with tube current of 80 mA in calcium score,delayed time detection of Smart Prep,and ECG-gated tube current modulation,the radiation dose of coronary angiography with 64 MSCT could be reduced increasingly,and image quality achieves the diagnostic desire.