| Objective:Computed tomography (CT) coronary angiography has been widely used since the introduction of multi-slice scanners technology, but high radiation doses have been reported. Prospective ECG-gating using'step- and- shoot'axial scanning protocol has been shown to reduce radiation exposure effectively while maintaining diagnostic accuracy. 256-slice scanners with 80 mm detector coverage have been currently introduced into practice, but their impact on radiation exposure has not been adequately studied. The aim of this study was to assess radiation doses associated with CT coronary angiography using a 256-slice CT scanner. radiation doses were estimated for 60 patients scanned with either prospective or retrospective ECG-gating.Methods:Our initial study cohort included 60 patients who were referred for CTCA at our department . Radiation dose estimates were expressed in the volume CT dose index (CTDIvol), dose–length product (DLP) and effective dose (ED).The CTDIvol was provided by the CT scanner.The dose–length product is defined as the CTDIvol multiplied by scan length.To obtain the effective dose, dose–length product was multiplied by an appropriate gender and body habitus averaged conversion coefficient for the adult thorax (k =0.014 mSv mGy?1 cm?1).Image quality was assessed objectively in terms of mean CT attenuation at selected regions of interest on axial coronary images and subjectively by coronary segment quality scoring.Results:It was found that radiation doses associated with prospective ECG-gating were significantly lower than retrospective ECGgating (3.7±0.9 mSv versus 18.0±6.5 mSv),reducing radiation dose by 79%. No statistically significant differences in image quality were observed between the two scanning protocols for both objective and subjective quality assessments.Conclusion:With the use of PT CTCA , radiation dose is markedly reduced and optimal image quality is maintained.
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