Free fatty acid-based low-impedance liver image: a characteristic appearance in nonalcoholic steatohepatitis (NASH)

BACKGROUND: To examine in vitro acoustic property of nonalcoholic fatty disease in mouse and human liver to identify nonalcoholic steatohepatitis (NASH). METHODS: The acoustic impedance (× 10(6) kg/m(2)/s) was measured in 35 free fatty acids (FFAs, 500 mmol/L) and histologically-diagnosed liver samples of twelve mice (four control, four simple steatosis [SS], and four NASH) and eight humans (two control, three SS, and three NASH), using 80-MHz acoustic microscopy. The sum of percentage (SP) composition of FFAs (SP-FFAs) was also assessed. RESULTS: Median impedance of all FFAs was 0.7 (5 FFAs with impedance 0.7); 17 FFAs with impedance < 0.7 were classified as low-impedance group; and, 13 FFAs with impedance > 0.7 were classified as high-impedance group. The median impedance of the mouse liver decreased from control (1.715), to SS (1.68), to NASH (1.635) (control versus NASH, p = 0.039 without significant differences for the other comparisons, p ≥ 0.1). Similarly, the median impedance of human liver showed decreased from control (1.825), to SS (1.788), to NASH (1.76) (control versus SS, p = 0.023; control versus NASH, p = 0.003; SS versus NASH, p = 0.050). The ratio of SP-FFAs between the low-impedance and high-impedance groups showed an increase in both mice and humans, with significant differences in mice (control versus SS, p < 0.001; control versus NASH, p < 0.001; SS versus NASH, p = 0.003), without significant differences in humans (p ≥ 0.671). CONCLUSION: Lower acoustic impedance based on the intrahepatic composition of FFAs may be characteristic of NASH.