Objective:Triple rule-out (TRO) computed tomographic angiography (CTA) is a protocol which allowsevaluation of coronary arteries, aorta, pulmonary arteries and adjacent intrathoracic structures forpatients with acute chest pain. Retrospective ECG-gated (RGH) is generally used for TRO CTA while thefeasibility of using ECG-gated tube current modulation (ETCM) or prospective ECG-triggering (PGT)protocols have not been fully investigated. The objective of this study is to investigate the potential fordose reduction through the use of ETCM and PGT in TRO CTA examination as compared with routine RGHprotocols.Material and methods:All TRO CTA examinations were performed on a 256-slice CT scanner using ananthropomorphic phantom. To determine equivalent doses for different organs, thermal-luminancedosimeters (TLDs) were placed in different positions in the organs during the scanning and effectivedoses were calculated based on ICRP-103 guidelines. Effective doses calculated from volume CT doseindex (CTDIvol) were also compared with those obtained from TLD measurements.Results:From the study, the mean effective dose for RGH, ETCM and PGT scanning was 21.54 mSv,15.52 mSv and 10.75 mSv respectively. The doses for ETCM and PGT techniques were significantlyreduced by 27% and 50% (p<0.01) as compared to that for RGH. Effective doses calculated from CTDImethod for three protocols were no significantly difference compared with those obtained from TLDmeasurements.Conclusion:Radiation dose could be efficiently reduced by applying the ETCM and PGT protocols in the256-slice TRO CTA examinations.