Rational arrangement of measuring shear wave speed in the liver

BACKGROUND: Shear wave speed has been widely applied to quantify a degree of liver fibrosis. However, there is no standardized procedure, which makes it difficult to utilize the speed universally. AIM: To provide procedural standardization of shear wave speed measurement. METHODS: Point shear wave elastography (pSWE) was measured in 781 patients, and two-dimensional shear wave elastography (2dSWE) was measured on the same day in 18 cases. Regions-of-interest were placed at 12 sites, and the median and robust coefficient-of-variation (CVR) were calculated. A residual sum-of-square (Σdi(2)) was computed for bootstrap values of 1000 iterations in 18 cases with each assumption of 1 to 12 measurements. The proportion of the Σdi(2) (%Σdi(2)) was calculated as the ratio of Σdi(2) to pSWE after converting it based on the correlation between pSWE and 2dSWE. RESULTS: The CVR showed a significantly broader distribution in the left lobe (P < 0.0001), and the smallest CVR in the right anterior segment that covered 95% cases was 40.4%. pSWE was significantly higher in the left lobe than in the right lobe (1.63 ± 0.78 m/s vs 1.61 ± 0.78 m/s, P = 0.0004), and the difference between the lobes became further discrete when the subjects were limited to the cases with a CVR less than 40.4% in any segment (1.76 ± 0.80 m/s vs 1.70 ± 0.82 m/s, P < 0.0001). The highest values of the CVR in every 0.1 m/s interval were plotted in convex upward along pSWE and peaked at 1.93 m/s. pSWE and 2dSWE were significantly correlated (P < 0.0001, r = 0.95). In 216000 resamples from 18 cases, the %Σdi(2) of 12 sites was 8.0% and gradually increased as the acquisition sites decreased to reach a significant difference with a %Σdi(2) of 7 sites (P = 0.027). CONCLUSION: These data suggest that shear wave speed should be measured at 8 or more sites of spreading in both lobes.