Size-Specific Dose Estimates Based on Water-Equivalent Diameter and Effective Diameter in Computed Tomography Coronary Angiography

BACKGROUND: To determine the difference in size-specific dose estimates (SSDEs), separately based on effective diameter (deff) and water equivalent diameter (dw) of the central slice of the scan range in computed tomography coronary angiography (CTCA). MATERIAL/METHODS: There were 134 patients who underwent CTCA examination, were electronically retrieved. SSDEs (SSDE(deff) and SSDE(dw)) were calculated using 2 approaches: deff and dw. The median SSDEs and mean absolute relative difference of SSDEs were calculated. Linear regression model was used to assess the absolute relative difference of SSDEs based on the ratio of deff to dw. RESULTS: The median values of SSDE(deff) and SSDE(dw) were 18.26 mGy and 20.56 mGy, respectively (P<0.01). The former was about 10.08% smaller than the latter. The mean absolute relative difference of SSDEs was 10.48%, ranging from 0.33% to 24.16%. A considerably positive correlation was found between the absolute relative difference of SSDEs and the ratio of deff to dw (R(2)=0.9561, r=0.979, P<0.01). CONCLUSIONS: The value of SSDE(deff) was smaller by an average of about 10.08% than SSDE(dw) in CTCA, and the absolute relative difference increased linearly with the ratio of effective diameter to water equivalent diameter.