Quantitative Detection Efficiency of UDFF for Nonalcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide characterized by excessive accumulation of triglycerides in hepatocytes and subsequent steatosis, affecting more than 25 % of the population globally. Approximately 20 % - 25 % of NAFLD patients can develop nonalcoholic steatohepatitis (NASH), which leads to more rapid progression from fibrosis to cirrhosis, and even liver failure or hepatocellular carcinoma (HCC). NALFD is strongly associated with metabolic risk factors, such as obesity, cardiovascular disease, and diabetes mellitus. Early detection and treatment may halt or reverse NAFLD progression. However, the occurrence and progression of steatosis and fibrosis had no obvious clinical symptoms, resulting in a difficulty of early diagnose and grade individuals with NAFLD clinically.

Although liver biopsy has been the well-accepted clinical reference standard for both diagnosis and staging of the different histological changes in NAFLD, this procedure is invasive with complications such as bleeding and infection, and is unreliable for quantifying steatosis due to sampling errors. Several imaging modalities have been used to diagnose and grade hepatic steatosis. Magnetic resonance imaging-derived proton density fat fraction (MRI-PDFF) currently has been accepted as the preferred alternative to the histological assessment of hepatic steatosis in patients with NAFLD. Magnetic resonance elastography (MRE) provide additional information of inflammation and fibrotic components of NAFLD. However, important limitations hinder the widespread clinical application of MRI, including high cost, low availability, long scan times and exclusion of patients with metal implants.

Ultrasound (US) has been recommended by several guidelines as the first-line screening tool for patients at risk of NAFLD. The most commonly used noninvasive method that quantifies the amount of fat in the liver is the controlled attenuation parameter, and more than 10% of steatosis can be distinguished. The disadvantages of this technique are that the liver morphological changes cannot be assessed simultaneously and poor performance in patients with higher body mass indices, leading to a failure rate of measurement ranged of 7.7 % - 14.0 %.

The developed ultrasound-derived fat fraction (UDFF) is designed to assess hepatic steatosis by estimating the frequency-dependent attenuation coefficient (AC) and backscatter coefficient (BSC) through processing acoustic radiofrequency (RF) signals returned from the liver tissue as fat vesicles in hepatocytes have a different characteristic impedance compared to normal liver tissue. UDFF is available on the Acuson Sequoia ultrasound system (Simens Healthineers, Mountain View, CA, USA), with reference to integrated phantom data to correct for system impact, and produces a UDFF value presented as a fat fraction (%), which is potentially related to MRI-PDFF and can be directly compared with MRI-PDFF. In addition, automatic point shear wave elastography (auto-pSWE) is available on the Acuson Sequoia ultrasound system to obtain liver stiffness measurement (LSM) for assessing hepatic fibrosis, simultaneously with UDFF measurement. The prospective, multicenter study aims to evaluate the efficiency of UDFF as a quantitative non-invasive alternative for NAFLD.