The value of SSDE based on effective diameter and water equivalent diameter in pediatric head CT / 中华放射医学与防护杂志

ABSTRACT

Objective:To explore the value of size-specific dose estimate (SSDE) based on effective diameter and water equivalent diameter ( Dw) in pediatric head CT. Methods:A retrospective analysis of 187 children underwent unenhanced head CT scanning were reviewed and divided into 3 groups according to the age Group 1 (<1 m), Group 2(≥1 m~6 y), Group 3 (≥6~14 y). All CTDI vol values were recorded. The central axial image in the scanning range was selected. The region of interest (ROI) containing all anatomical structures (including skin) was outlined and the area of ROI ( AROI), head circumference, average CT value (CT ROI) were measured. The Dw, conversion factor fH16 and SSDE were calculated. The CTDI vol, SSDE and the rate of change( &Delta;value)were compared among groups. The regression model between CTDI vol and SSDE was established. Results:The Dw values of groups 1-3 were (11.24±0.51), (14.48±1.47), (16.69±0.90)mm, respectively. The CTDI vol values were(15.36±2.78), (18.83±4.60), (23.24±4.13)mGy, respectively. SSDE values were(27.92±4.91), (29.16±6.64), (32.38±5.35)mGy, respectively. The differences among Dw, CTDI vol and SSDE groups were all statistically significant ( F=207.69、38.48、8.15, P<0.001). The values of Dw, CTDI vol and SSDE were gradually increasing while the age was increasing. However, the &Delta; value gradually was decreasing with increasing age. The linear regression equation of CTDI vol and SSDE was established as SSDE=7.252 + 1.137×CTDI vol. Conclusions:The radiation dose of children′s head CT can be accurately assessed based on Dw combined with head conversion factor fH16 to estimate the body-specific dose SSDE. The radiation dose of children′s head CT was underestimated with the greater degree for smaller age.