摘要目的 探讨CT冠状动脉成像基于有效直径(effective diameter,def)和水等效直径(water equivalent diameter,dw)的体型特异性剂量估算值(size-specific dose estimate,SSDE)差异,并分析原因.方法 回顾性收集90例因可疑或确诊冠状动脉粥样硬化性心脏病行CT冠状动脉成像的患者.以def和dw对应的体型转换系数(size-dependent conversion factor,f)与容积CT剂量指数(volume CT index,CTDIvol)的乘积计算SSDEdef和SSDEdw,分别记为A组和B组.计算SSDEdef和SSDEdw的平均绝对相对误差(mean absolute relative difference,MARD),并以多元逐步线性回归分析扫描区域不同组织结构对MARD的影响.结果 def和dw均与体质量指数(body mass index,BMI)呈正相关(r=0.869、0.823,P<0.05).SSDEdef、SSDEdw的中位数(四分位数间距)分别为12.34(11.75,12.98)mGy、13.78(13.02,15.04)mGy,SSDEdef较SSDEdw约低10.45％,差异具有统计学意义(Z=-8.186,P<0.05).两者均与BMI和dw呈负相关(r=-0.765、-0.680,-0.701、-0.840,P<0.05).SSDEdef与SSDEdw总体平均MARD为11.39％.MARD与BMI相关性无统计学意义(P>0.05),但与def呈正相关(r=0.251,P<0.05),与dw呈负相关(r=-0.379,P<0.05).影响MARD的因素中,骨骼和强化心腔血管的CT值(SIhigh)、 脂肪面积(Areafat)和CT值(SIfat)、 软组织的CT值(SIsoft)未进入回归方程,MARD与含气肺组织的面积(Arealow)和软组织的面积(Areasoft)独立正相关(β=0.634、0.102,P<0.05),与高衰减结构面积(Areahigh)和含气肺组织的CT值(SIlow)呈独立负相关(β=-0.234、-0.343,P<0.05).结论 CT冠状动脉成像的SSDEdef较SSDEdw约低10.45％,低衰减结构面积占比是影响估算剂量差异的最重要的独立因素.

abstractsObjective To investigate the difference of size-specific dose estimates ( SSDEs ) based on effective diameter ( def ) 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 ( SSDEd ef and SSDEdw ) were calculated in two approaches using def and dw , respectively. Mean absolute relative difference ( MARD) was computed as an index to quantify the consistency of SSDEd ef and SSDEdw . Multivariate stepwise regression analysis was performed to study the factors influencing MARD. Results The values def and dw were positively correlated with body mass index (BMI) (r=0. 869, 0. 823, P<0. 05). The median (interquartile range) of SSDEdef and SSDEdw were 12. 34 ( 11. 75, 12. 98) mGy, 13. 78 ( 13. 02, 15. 04) mGy, respectively. SSDEdef was lower by 10. 45％ than SSDEdw( Z=-8. 186, P<0. 05) . Both SSDEdef and SSDEdw were negatively correlated with BMI and dw(r=-0. 765, -0. 680, -0. 701, -0. 840, P<0. 05). MARD of SSDEdef and SSDEdw was&nbsp;generally at 11. 39％. No statistical significance was found in the correlation of MARD with BMI ( r=0. 031, P>0. 05) , however, positive correlation was shown between MARD and def ( 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 SSDEdef 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.