Speed of sound evaluation of organelles of NASH livers in rats with 250-MHz ultrasound

Non-invasive diagnosis of non-alcoholic steatohepatitis (NASH) can be achieved by quantitative ultrasound (QUS), which requires a detailed understanding tissue-specific acoustic microstructure at cellular scale (i.e., 10 μm). This study focuses on obtaining speed of sound (c) of organelles (i.e., nucleus, cytoplasm, and fibers) using 250-MHz ultrasound in rat livers. Three different pathological stages were investigated in rat models: normal (control: n = 2), NASH (n = 3), and fibrosis model (n = 6). After animal sacrifice, each liver was fixed in formalin and a 7-μm thin section was affixed to glass slide using a microtome. A scanning acoustic microscopy system equipped with a 250-MHz center-frequency transducer was employed to obtain two-dimensional (2D) maps of c with a spatial resolution of 7-μm. The histological images were used to detect the positions of the nuclei, cytoplasm and fibers, and the corresponding c values from obtained from the co-registered 2D c map. For all organelles, Kruskal-Wallis test reveals a significant difference (p < 0.01) between all paired stages. These results reveals that c is the highest in fibrosis livers for all organelles. Additionally, in NASH livers, c of nuclei and cytoplasm were the lowest, which could be due to intracellular fluid or ballooning of the whole cell. As expected, c in fiber changes with pathologic state. Results reveal that c of the nucleus and cytoplasm also changes with pathologic state and that we were able to carefully assess these differences using 250-MHz ultrasound. These results could prove invaluable to improve in vivo QUS investigations of livers.