肾及肾透明细胞癌多b值扩散成像的单双指数拟合比较

Comparison of fi tting degree in monoexponential and biexponential model used to assess multi b-value DWI of renal parenchyma and CCRCC

目的探讨一种更适合描述肾实质和肾透明细胞癌(clear cell renal cell carcinoma,CCRCC)的DWI信号强度随b值变化的数学函数模型。材料与方法通过回顾性分析32例CCRCC患者的影像学资料。参考常规图像,分别测量肾实质和CCRCC实质区的DWI信号强度,分别采用单、双指数函数的数学模型对DWI信号拟合。两种拟合方法间的比较采用Wilcoxon检验;两种组织间的比较采用Mann-Whitney检验。结果两种组织的DWI信号强度均随着b值的增大而减小。肿瘤实质区的单、双指数拟合度参数R2的中位数(75%区间)分别为0.97(0.96,1.00)和1.00(1.00,1.00),组间存在统计学差异(W=-253,P=0.00);肾脏实质的单、双指数拟合度参数R2的中位数(75%区间)分别为0.98(0.98,0.99)和1.00(1.00,1.00),组间存在统计学差异(W=-528,P=0.00)。两种组织间的R2都无统计学差异(U=301.5,P=0.26;U=253.0,P=0.05)。结论双指数函数模型比单指数函数更适合于描述肾实质和CCRCC的DWI信号强度随b值的变化规律。

Objective：To explore a more suitable mathematical model describing the signal change of renal parenchyma and clear cell renal cell carcinoma （CCRCC） induced from DWI with several b values. Materials and Methods： The images of 32 cases with CCRCC was analyzed retrospectively. Base on the conventional sequences, the signal intensity of renal parenchyma and CCRCC were measured, and the trends of signal intensity with several b values were fitted using two methods respectively, including monoexponential model （Group 1） and biexponential model （Group 2）, and the quantitative index R2 was calculated. The R2 was compared between two groups using Wilcoxon test and between two tissues using Mann-Whitney test. Results： The signal intensity of two tissues declined with increased b values. The R2 was shown as median （75% CI）. In tumor, the R2 is 0.97 （0.96, 1.00） in Group 1 and 1.00 （1.00, 1.00） in Group 2, and a significant difference was found （W=-253, P=0.00）. In renal parenchyma, the R2 is 0.98 （0.98, 0.99） in Group 1 and 1.00 （1.00, 1.00） in Group 2, and there is a statistical difference （W=-528, P=0.00）. And there are no differences between two tissues using each exponential modal （U=301.5, P=0.26, U=253.0, P=0.05, respectively）. Conclusion： The biexponential function is a more suitable mathematical model for describing the signal change of renal parenchyma and CCRCC on DW imaging with several b values.