Non-invasive staging of hepatic steatosis using computer-aided ultrasound diagnosis

In this study, a computer-aided ultrasound (CAUS) diagnostic method for the detection and staging of hepatic steatosis (non-alcoholic fatty liver disease, NAFLD) is investigated using a bovine model (n=151). In humans as well as in cows, hepatic steatosis increases the risk of co morbidity. Assessment of liver fat content is mostly done by taking liver biopsies. The authors' goal was to estimate the liver fat content by using echographic parameters, i.e., non-invasively. Since skin and subcutaneous fat layer influence the characteristics of echographic B-mode liver-images, both transcutaneous and intraoperative images were acquired to study this effect. During image acquisition a fixed preset of the ultrasound equipment controls was used. One liver biopsy was taken from each animal to stage the NAFLD. Apart from the fat percentage, the triglyceride (TG) level was biochemically assessed and used in this study. The software package CAUS was developed to perform objective and unambiguous analysis on echographic B-mode images. Prior to image analysis, certain preprocessing steps were performed in order to achieve the relative echo strength in decibel (dB), rather than image gray level, as a quantitative parameter. Furthermore, corrections were made for ultrasound propagation through skin/fat layer and through an average ldquohealthy liverrdquo (automatic gain control, AGC). After these corrections, the estimated echographic parameters were correlated to the TG level by uni- and multivariate linear regression analysis. The regression formula was then used to predict the TG level in each animal. A retrospective classification was performed and ROC curves were obtained. High correlations with the liver TG score were found for several echographic and image parameters. ROC curve analysis show promising results for sensitivity (0.93), specificity (0.86) and area under the curve (0.93) in distinguishing fatty livers from healthy livers. This study showed the feasibility of computer-aided ultrasound for non-invasively diagnosing, or even screening, of liver steatosis.