基于水当量直径体型特异性剂量估计在儿童头部CT检查中的价值

The value of SSDE based on effective diameter and water equivalent diameter in pediatric head CT

目的探讨基于水当量直径(Dw)体型特异性剂量估计(SSDE)在评价儿童头部CT辐射剂量的价值。方法回顾性分析首都儿科研究所附属儿童医院头颅CT平扫患儿187例, 按年龄分为3组, 1组(<1月)、2组(≥1月~6岁)、3组(≥6 ~14岁)。记录剂量报告容积CT剂量指数(CTDIvol)值。扫描范围中心层面选取CT轴位图像, 勾画包含所有解剖结构(包括皮肤)的感兴趣区(ROI), 测量ROI面积(AROI), 头围以及平均CT值(CTROI)。计算Dw、转换因子(fH16)以及SSDE。组间比较CTDIvol、SSDE值及其变化率(Δ值), 建立CTDIvol与SSDE关系的回归模型。结果各组Dw分别为(11.24±0.51)、(14.48±1.47)、(16.69±0.90)mm;CTDIvol分别为(15.36±2.78)、(18.83±4.60)、(23.24±4.13)mGy;SSDE分别为(27.92±4.91)、(29.16±6.64)、(32.38±5.35)mGy。Dw、CTDIvol以及SSDE组间差异有统计学意义(F=207.69、38.48、8.15, P<0.001)。随年龄增加, Dw、CTDIvol以及SSDE值均逐渐增加。Δ值逐渐减低, 随着年龄增加, 差异度逐渐减小。建立CTDIvol与SSDE线性回归方程为SSDE=7.252+1.137×CTDIvol。结论基于Dw联合头部转换因子fH16进行体型特异性剂量估算SSDE, 可精确评估患儿头部CT扫描辐射剂量。CTDIvol低估了儿童头部CT辐射剂量, 年龄越小, 辐射剂量被低估的程度越大。

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 CTDIvol 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(CTROI)were measured.The Dw,conversion factor fH16 and SSDE were calculated.The CTDIvol,SSDE and the rate of change(Δvalue)were compared among groups.The regression model between CTDIvol 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 CTDIvol 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,CTDIvol and SSDE groups were all statistically significant(F=207.69、38.48、8.15,P<0.001).The values of Dw,CTDIvol and SSDE were gradually increasing while the age was increasing.However,theΔvalue gradually was decreasing with increasing age.The linear regression equation of CTDIvol and SSDE was established as SSDE=7.252+1.137×CTDIvol.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.