2-dimensional shear wave elastography: Interobserver agreement and factors related to interobserver discrepancy

Purpose
To evaluate the interobserver reproducibility of two-dimensional shear wave elastography (2D-SWE) in measuring liver stiffness (LS) and to investigate factors related to liver 2D-SWE.
Materials and methods
A prospective study was conducted between August 2011 and August 2012 in rheumatoid arthritis patients who had been treated with methotrexate. Interobserver reproducibility of 2D-SWE was evaluated, and the relationship between interobserver difference in LS and related factors was analyzed using linear regression analyses. We considered age, sex, alanine transaminase, cholesterol, body mass index (BMI), and waist circumference as clinical factors, and the mean value of standard deviation (SDM), its difference between two examiners, mean diameter of the regions of interest (ROIM), and its difference in the elasticity map as investigation factors. The cut-off value for significant factors to predict interobserver discrepancies in LS-based fibrosis stage was also inspected.
Results
In total, 176 patients were enrolled. The intraclass correlation coefficient between the two examiners was 0.784. In the univariate analysis, SDM and ROIM were independently associated with interobserver differences in LS as well as BMI, waist circumference, and the difference of ROI, but SDM and ROIM were the only ones significantly related in multivariate analysis (p<0.001 and p = 0.021, respectively). The best cut-off value for SDM in predicting interobserver discrepancy in LS-based fibrosis stage was 1.4.
Conclusions
Interobserver reproducibility of 2D-SWE for measuring LS was good and SDM was the most significantly associated factor with interobserver differences in LS and interobserver discordance in LS-based fibrosis stage.

### 研究目的
本研究旨在评估二维剪切波弹性成像（two-dimensional shear wave elastography，2D-SWE）测量肝脏硬度（liver stiffness，LS）的观察者间重复性，并探讨与肝脏二维剪切波弹性成像相关的影响因素。

### 材料与方法
本研究为前瞻性研究，于2011年8月至2012年8月期间纳入接受甲氨蝶呤治疗的类风湿关节炎患者。评估2D-SWE的观察者间重复性，采用线性回归分析肝脏硬度测量值的观察者间差异与相关因素的关联。本研究纳入的临床因素包括年龄、性别、丙氨酸氨基转移酶、胆固醇、体质量指数（body mass index，BMI）及腰围；考察因素包括标准差均值（mean value of standard deviation，SDM）、两名检查者的SDM差值、感兴趣区平均直径（mean diameter of the regions of interest，ROIM）及其在弹性图中的差值。此外，本研究还考察了用于预测基于肝脏硬度的纤维化分期观察者间差异的显著因素的截断值。

### 结果
最终共纳入176例患者。两名检查者的组内相关系数为0.784。单因素分析显示，SDM、ROIM、BMI、腰围以及感兴趣区差值均与肝脏硬度的观察者间差异相关；但多因素分析结果显示，仅SDM与ROIM具有显著统计学相关性（分别为p<0.001和p=0.021）。用于预测基于肝脏硬度的纤维化分期观察者间差异的SDM最佳截断值为1.4。

### 结论
用于测量肝脏硬度的二维剪切波弹性成像（2D-SWE）观察者间重复性良好，且SDM是与肝脏硬度观察者间差异及基于肝脏硬度的纤维化分期观察者间不一致性关联最显著的因素。