Ultrasound Statistical Parametric Imaging in the Assessment of Fatty Liver

Abstract

Hepatitis steatosis may progress to nonalcoholic steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Nonalcoholic fatty liver disease (NAFLD) is the type of hepatic steatosis that most commonly leads to chronic liver disease. NAFLD is also related to metabolic risk factors. How to characterize fatty liver is attracting growing medical and health research interest. Notably, the speckle pattern is formed by ultrasound backscattered echoes, which are typically treated as random signals. Thus, analyzing the statistical distribution of the echo amplitude (i.e., the envelope signal) may provide useful clues associated with fatty liver diseases. Many investigators have began to study the relationship between the probability property of inverse scattering and the characteristics of tissue. Commonly used statistical models include the Rayleigh distribution, Rician distribution, K distribution, homodyned K distribution, Nakagami distribution, and compounding Nakagami distribution. One requisite of using statistical models to fit echo amplitude distributions is that the ultrasound envelope data must conform to the used distribution. To overcome the limitations mentioned above, we need to set a new direction for constructing the images of ultrasound parameters outside the statistical model ultrasonic method. Recall that Shannon established information theory and defined entropy as a measure of information uncertainty. Hughes pioneered using Shannon entropy for analyzing ultrasound signals, indicating that entropy is able to quantitatively describe changes in the microstructures of scattering media. Recently, we also developed the small-window entropy image of ultrasound by using a simple model of histograms and defined the weighted entropy to provide greater sensitivity in diagnosing the changes of the scattering microstructures of tissues. The results showed that fatty infiltration increases the uncertainty of backscattered signals from livers. Ultrasound entropy imaging has potential for the routine examination of fatty liver disease.