The added value of quantitative ultrasound to shear wave elastography for assessment of steatohepatitis in a rat model

Abstract

Non-alcoholic fatty liver disease is a highly prevalent condition, which may progress to non-alcoholic steatohepatitis (NASH), an advanced form found in 3 to 5% of the population. As liver biopsy is invasive, there is a need for a non-invasive technique for the assessment of NASH. Due to promising results of shear-wave elastography (SWE) in staging this disease, there is a high interest in developing a multi-parametric approach for assessment of liver steatosis within the same ultrasound (US) examination. The goal of this study was to assess the added value of quantitative US (QUS) parameters to SWE, based on random forest classifiers and area under the ROC curve (AUC). Sixty male Sprague-Dawley rats were either fed a standard chow or a methionine-and choline-deficient diet. Using a research US system (model V1, Verasonics Inc.), SWE measurements were performed while rats were under anesthesia. To generate shear wavefronts within the liver, a linear array US transducer (ATL L7-4, Philips) was used to induce three 40-V 125-μs long radiation force pushes 4 mm apart. For SW tracking, the same transducer was used to acquire plane wave radiofrequency data at a frame rate of 4 kHz; images were reconstructed using the f-k migration algorithm. QUS acquisitions were performed using the same system and transducer. One hundred frames were acquired, migrated, and the echo envelope was obtained with Hilbert transforms. The image post-processing yielded 4 homodyned-K parametric maps within the region-of-interest (ROI), from which 8 features were extracted. The local attenuation coefficient slope within the ROI was also computed using the spectral shift method. QUS parameters improved the classification accuracy of steatohepatitis, liver steatosis, inflammation, and fibrosis compared to SWE alone. For detection of liver steatosis grades 0 vs ≥ 1, ≤ 1 vs ≥ 2, ≤ 2 vs 3, respectively, AUCs increased from 0.70, 0.65, and 0.69 to 0.78, 0.78, and 0.75 (p < 0.001).