2-D Shear Wave Elastography for Focal Lesions in Liver Phantoms: Effects of Background Stiffness, Depth and Size of Focal Lesions on Stiffness Measurement

The aim of this study was to determine the factors influencing stiffness and conspicuity of focal lesions in deep organs by focusing on target properties using 2-D shear wave elastography (SWE). Two normal (4 ± 1 kPa) and cirrhotic (16 ± 2 kPa) liver-mimicking phantoms with spherical inclusions (23 ± 3 kPa) were used. Inclusions of three sizes (20, 15 and 10 mm in diameter) were arranged in a row at depths of 3, 5 and 7 cm. Two observers acquired quantitative stiffness values and a qualitative five-grade morphologic score at each inclusion using SWE. The coefficients of variation (CVs) of stiffness were calculated to assess measurement reliability. The generalized estimating equation was used to identify whether stiffness, CV and morphologic score were independent of background stiffness, depth and size of inclusions and observer. In the quantitative assessment, stiffness of the inclusion and CV were dependent on the type of phantom and depth of inclusion (p < 0.001). There were no significant differences in stiffness and CV according to the observer. Morphologic score differed significantly only in the size of the inclusion (p < 0.001). When the depth of the inclusion was 7 cm, the stiffness was the highest, and the 10 mm-sized inclusions had lower morphologic scores than the other inclusions (all p values < 0.001). In conclusion, 2-D SWE assessment of focal lesions could be affected by background stiffness and depth of focal lesions, and may be limited in evaluating focal hepatic lesions.