How the measurement depth influences the liver stiffness assessment using real-time shear wave elastography (SWE)

The purpose of this study was to evaluate the influence of measurement depth on the results of real-time shear wave elastography (SWE) measurements and to find a reliable measurement depth range for liver stiffness assessment using SWE. SWE measurements were performed on an Elasticity Quality Assurance phantom and healthy volunteers' livers. The different depths from probe surface and from liver capsule were studied in 30 and 88 healthy volunteers, separately. The success rate of measurements (SRoM), success rate of subjects (SRoS), and coefficients of variation (CV) of repeated measurements were calculated and compared. In phantom study, the CV at 2-6cm depth (from 0.6 % to 0.9 %) was larger than those at the other depths (from 2.8 % to 9.8 %). For the first group of healthy volunteers, the SRoMs at 3-7cm depths were significantly higher than the others, and the measured results were found to be more reliable at 2-5cm (P<0.001). In the second group of subjects, the SRoSs at 1-4cm depths below liver capsule were all 100 % but at 0-1 cm depth was zero. According to our results, the most reliable depth range of liver stiffness assessment using SWE should be 3-5cm from the probe surface and simultaneously 1-2cm below the liver capsule.