Liver Fat Droplet Dependency on Ultrasound Backscatter Coefficient in Nonalcoholic Fatty Liver

Quantitative ultrasound (QUS) techniques are diagnostically useful in assessing nonalcoholic fatty liver disease (NAFLD). From previous studies, the backscatter coefficient (BSC) correlates with liver fat fraction, but the mechanisms have not been determined. Understanding the ultrasound scattering mechanisms will lead to better acoustic scattering models and more accurate diagnostics. The purpose of this study is to test the following hypothesis: Fat droplet deposition in hepatocytes alters the locations of hepatocyte nuclei, changing the spatial distribution of the nuclei, which leads to the change in the structure function (SF), a factor of the BSC. The SF, determined by the distribution of the nuclei, is correlated with the fat fraction. To test this hypothesis, hematoxylin and eosin-stained liver histopathological slides from 48 participants were digitized (40×). One to 5 regions (453.6 µm × 453.6 µm) were selected from each participant's slide(s), yielding 218 images in total. For each image, hepatocyte nuclei and fat droplets each were automatically recognized. SF versus frequency was calculated from the nuclear distribution. Liver fat fraction was determined from the fractional surface area of fat droplets. SF was positively correlated with the liver fat fraction (Pearson's r 0.4, p < 10-4) below 30 MHz (including clinically relevant frequencies 3 - 5 MHz). In conclusion, this study shows the fat droplets change the distribution of hepatocyte nuclei, which is a factor contributing to the correlation between fat fraction and BSC.