Comparative analysis of size-specific dose estimates in coronary computed tomography angiography

Objective To investigate the difference of size-specific dose estimates (SSDEs) based on effective diameter (deff) and water equivalent diameter (dw) in coronary computed tomography angiography (CCTA) and explore the causes. Methods A total of 99 patients undergoing CCTA were enrolled in this retrospective study. SSDEs (SSDEdeff and SSDEdw) were calculated in two approaches using deff and dw, respectively. Mean absolute relative difference (MARD) was computed as an index to quantify the consistency of SSDEdeff and SSDEdw. Multivariate stepwise regression analysis was performed to study the factors influencing MARD. Results The values deff and dw were positively correlated with body mass index (BMI) (r=0.869, 0.823, P 0.05), however, positive correlation was shown between MARD and deff (r=0.251, P<0.05), but negative correlation for MARD and dw (r=-0.379, P<0.05). With respect to the factors influencing MARD, four variables were included into the regression equation. MARD was positively correlated with the area of both air-filled lungs (Arealow) and soft tissues (Areasoft) (β=0.634, 0.102, P<0.05), and negatively correlated with the area of bone, enhanced cardiac chambers and aorta (Areahigh) and the CT value of air-filled lungs (SIlow) (β=-0.234, -0.343, P<0.05). Conclusions SSDEdeff was approximately 10.45% lower than SSDEdw, which was predominantly influenced by the area of air-filled lungs due to the characteristics of low X-ray attenuation in CCTA. Key words: Coronary vessels; Tomography, X-ray; Size-specific; Dose estimation