Measurement of acoustic impedance for normal, fibrosis and NASH livers by using bio-acoustic microsropy

Early diagnosis for non-alcoholic steatohepatitis (NASH) is desired because it may progress to cirrhosis or finally hepatocellular carcinoma in the severe case. To propose the possible noninvasive diagnosis using ultrasound, we aim to summarize the change of the tissue property. As a basic study, this report demonstrates the acoustic impedance of mouse livers in case of the normal, the liver cirrhosis and the NASH model using bio-acoustic microscopy. To measure the acoustic impedance, a transducer with 80-MHz center frequency, which is incorporated in a bio-acoustic microscopy system, was employed. The value could be calculated based on the analysis of the echo amplitude, and 2D image of acoustic impedance can be obtained by scanning the transducer. The 2D image demonstrated that the tissue structure is homogeneous in normal liver. In contrast, the pattern of random granular texture like lipid droplet was found in NASH liver. Based on statistical analysis, it was found that the acoustic impedance in case of NASH is lowest among all models.