Relationship between liver tissue stiffness and histopathological findings analyzed by shear wave elastography and compression testing in rats with non-alcoholic steatohepatitis

Purpose The aim of the present study was to investigate two methods of determining liver stiffness in rats with various degrees of non-alcoholic steatohepatitis induced by a methionine- and choline-deficient (MCD) diet by comparing each finding with reference to histopathological liver findings. Methods Twenty male Wister rats were fed an MCD diet for up to 32 weeks, and four were fed a normal diet. Ultrasound-based shear wave elastography (SWE) and mechanical compression testing using an Instron Universal Testing machine were performed on each rat at designated time points. After each examination, liver histopathology was analyzed to evaluate the degrees of steatosis, inflammation, and fibrosis based on non-alcoholic fatty liver disease (NAFLD) activity score, and each finding was compared with reference to liver histopathologic findings. Results Median liver stiffness values measured using SWE showed a stepwise increase with increasing histological inflammation score ( P = 0.002), hepatic fibrosis stage ( P = 0.029), ballooning score ( P = 0.012), and steatosis grade ( P = 0.030). Median liver stiffness measured using an Instron machine showed a stepwise increase only with increasing histological fibrosis stage ( P = 0.033). Conclusions Degree of liver stiffness measured by SWE and the Instron machine differed. SWE reflected mainly inflammation, whereas Instron machine-derived values primarily reflected fibrosis. This is the main source of discrepancies between measurements made with these two modalities.