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

Abstract

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.

Fig 1. US elastography image for measurement of liver stiffness.

The trapezoidal colored box shows the distribution of elasticity in liver tissue, and the round ROI (Q-box) is located to measure elasticity. Measured values are displayed on the right side of the screen: Mean is the mean value of elasticity in the ROI; Min is the minimum elasticity; Max is the maximum elasticity; Std Dev is the standard deviation of elasticity in the ROI; and Diam is the diameter of the ROI.

Fig 2. Diagram of subject enrollment.

Fig 3. Correlation of liver stiffness (A) and mean value of standard deviation in the region of interest (B) between examiners 1 and 2.

The ICC values are 0.783 for liver stiffness and 0.521 for SD^M, respectively.

Fig 4. ROC curves for predicting interobserver discrepancies in liver fibrosis determined by 2D-SWE.