DISCUSSION
coronary artery stenosis
CORONARY ARTERY STENOSIS
In this study, we refined the currently used weight grouped protocol for CCTA in terms of the radiation and contrast medium dose through clinical evaluation. Given that no significant difference was found in objective image quality between subgroups, the optimal setting for each weight group was determined by the subjective image quality in combination with the applied radiation dose, where the subjective image quality was compared in terms of the percentage of cases being graded excellent, that is, receiving a score of 4. The detailed and comprehensive optimal scanning protocol was obtained by using the tentative approach in each body weight group, which provided diagnostically sufficient image quality for clinical diagnosis while reducing radiation dose and iodine intake.The patients < 55  or > 85 kg was additionally carried out with a small number of cases. Two scanning protocols, one routine protocol (In this study, the applied radiation dose was represented by the planned volume CT dose index (CTDIBody mass index (BMI) has been used in prior studies as the grouping factor for patients. Yuan et al. explored the feasibility of low tube voltage and IDR determined by patients’ BMI in CCTA.The present study had several limitations. First, the left circumflex artery was not considered in the objective image quality evaluation since the individual difference on circumflex artery is naturally quite large, which might complicate the evaluation of image quality. Second, while focused on image quality, the coronary artery stenosis found on CCTA images was not used, either as an extra grouping factor for image quality analysis or as a task for detectability test. This was in part due to the lack of gold standard of the diagnostic results. Third, this study considered only the hybrid iterative reconstruction that has been widely available with current commercial CT systems. It is of interest to investigate the same topic with emerging CT algorithms, such as deep‐learning based reconstruction, where the findings might be surprisingly different. Fourth, the automated exposure control (AEC) technique was not considered in this study, which would also be a reasonable starting point for optimization and worth comparing with the obtained parameter settings. Finally, the CCTA protocol refined in this study was only one scanner‐specific implementation. Care must be taken when translating the findings in this study to other CT models. The most determining factors are tube output, scanning geometry, and the image reconstruction method. Direct translation or scaling without a separate investigation is hardly reliable, even for those with similar wide detectors allowing volumetric CCTA in axial mode. However, the demonstrated investigative strategy for determining the optimal setting should be directly applicable to other scenarios, which is more essential than the exact value of the parameters.