To explore the feasibility of viscoelastic parameters based on the indentation relaxation test in evaluating liver fibrosis, so as to provide valuable parameters and methods for elastography in diagnosing liver fibrosis.

Fifty male SD rats with an average body mass of (180±20) g were selected and divided into two groups: a liver fibrosis group (n=40) and a control group (n=10). Finally, 43 SD rats were included, including 36 in the hepatic fibrosis group and 7 in the control group. Liver fibrosis was induced in rats with carbon tetrachloride, while the control group was fed olive oil solution alone. The indentation relaxation test was performed to determine the viscoelastic parameters of the liver after liver isolation. Liver fibrosis staging (stages S1~S4) was performed on isolated liver pathological specimens. The viscoelastic parameters of different liver fibrosis stages in rats were compared and the correlation between viscoelastic parameters and the degree of liver fibrosis in rats was analyzed.

Viscoelastic parameters τ₁, τ₂, and g₁ were statistically significant different between the groups (F=23.598, 2.836, and 2.506, respectively, all P<0.05). In further pairwise comparisons, τ₁ was statistically different between the control group and group S1, S2, S3, or S4 (t=2.367, 1.689, 2.887, and 3.195, respectively, all P<0.05). τ₂ was statistically different between groups S1 and S3 (t=2.048, P<0.05), and g₁ was statistically different between groups S2 and S3 (t=3.211, P<0.05). Spearman correlation analysis showed that viscoelastic parameters g₁ and g₁+ g₂ were positively correlated with the degree of liver fibrosis (r=0.513 and 0.439, respectively, both P<0.001), while τ₁ was negatively correlated with the degree of liver fibrosis (r=-0.509, P<0.001).

Viscoelastic parameters correlate with liver fibrosis stages, so it is feasible to use viscoelastic parameters to evaluate liver fibrosis stage in rats, which provides reliable experimental evidence for the application of viscoelastic parameters in shear wave elastography to evaluate liver fibrosis.