Tissue stiffness has long been known to be a biomarker of tissue pathology. Ultrasound elastography measures tissue mechanical properties by monitoring the response of tissue to acoustic energy. Different elastographic techniques have been applied to many different tissues and diseases. Depending on the pathology, patient-based factors, and ultrasound operator-based factors, these techniques vary in accuracy and reliability. In this review, we discuss the physical principles of ultrasound elastography, discuss differences between different ultrasound elastographic techniques, and review the advantages and disadvantages of these techniques in clinical practice.

).q RSNA, 2014 Purpose:To evaluate the accuracy of shear-wave elastography (SWE) for staging liver fibrosis in patients with diffuse liver disease (including patients with hepatitis C virus [HCV]) and to determine the relative accuracy of SWE measurements obtained from different hepatic acquisition sites for staging liver fibrosis. Materials and Methods:The institutional review board approved this single-institution prospective study, which was performed between January 2010 and March 2013 in 136 consecutive patients who underwent SWE before their scheduled liver biopsy (age range, 18-76 years; mean age, 49 years; 70 men, 66 women). Informed consent was obtained from all patients. SWE measurements were obtained at four sites in the liver. Biopsy specimens were reviewed in a blinded manner by a pathologist using METAVIR criteria. SWE measurements and biopsy results were compared by using the Spearman correlation and receiver operating characteristic (ROC) curve analysis. Results:SWE values obtained at the upper right lobe showed the highest correlation with estimation of fibrosis (r = 0.41, P , .001). Inflammation and steatosis did not show any correlation with SWE values except for values from the left lobe, which showed correlation with steatosis (r = 0.24, P = .004). Abbreviations: AUC = area under the ROC curve CI = confidence interval CLD = chronic liver disease DANA = difference between the mean fibrosis stage of advanced fibrosis and the mean fibrosis stage of nonadvanced fibrosis HCV = hepatitis C virus ROC = receiver operating characteristic SWE = shear-wave elastography Author contributions:Guarantors of integrity of entire study, A.E.S., M.D.; study concepts/study design or data acquisition or data analysis/ interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; agrees to ensure any questions related to the work are appropriately resolved, all authors; literature research, A.E.S., M.D., A.V., J.M.N., K.E.C.; clinical studies, A.E.S., A.V., A.K.B., J.M.N., K.E.C., R.T.C.; statistical analysis, M.D., E.F.H.; and manuscript editing, A.E.S., M.D., A.V., R.T.C. Funding:R.T.C. supported by the National Institutes of Health (grant DK078772).Conflicts of interest are listed at the end of this article. (1), with as many as 150 000 new cases diagnosed each year (2)-20% of which had cirrhosis at presentation. The multiple causes of CLD follow a common pathway of progressive liver fibrosis, ultimately culminating in cirrhosis. These include hepatitis C virus (HCV), hepatitis B virus, nonalcoholic fatty liver disease, and alcoholic liver disease (3). Although the prevalence of major causes of CLD remains stable, data from the National Health and Nutrition Examination Surveys show that nonalcoholic fatty liver disease will be a substantial burden on the prevalence of CLD in the United States (1). Advanced fibrosis, cirrhosis, and hepatocellular carcinoma develop in about 17%-55% of patients with HCV ...

Non-alcoholic fatty liver disease (NAFLD) is the most common diffuse liver disease, with a worldwide prevalence of 20% to 46%. NAFLD can be subdivided into simple steatosis and nonalcoholic steatohepatitis. Most cases of simple steatosis are non-progressive, whereas nonalcoholic steatohepatitis may result in chronic liver injury and progressive fibrosis in a significant minority. Effective risk stratification and management of NAFLD requires evaluation of hepatic parenchymal fat, fibrosis, and inflammation. Liver biopsy remains the current gold standard; however, non-invasive imaging methods are rapidly evolving and may replace biopsy in some circumstances. These methods include well-established techniques, such as conventional ultrasonography, computed tomography, and magnetic resonance imaging and newer imaging technologies, such as ultrasound elastography, quantitative ultrasound techniques, magnetic resonance elastography, and magnetic resonance-based fat quantitation techniques. The aim of this article is to review the current status of imaging methods for NAFLD risk stratification and management, including their diagnostic accuracy, limitations, and practical applicability.

Ultrasound (US) imaging is the most commonly performed cross-sectional diagnostic imaging modality in the practice of medicine. It is low-cost, non-ionizing, portable, and capable of real-time image acquisition and display. US is a rapidly evolving technology with significant challenges and opportunities. Challenges include high inter- and intra-operator variability and limited image quality control. Tremendous opportunities have arisen in the last decade as a result of exponential growth in available computational power coupled with progressive miniaturization of US devices. As US devices become smaller, enhanced computational capability can contribute significantly to decreasing variability through advanced image processing. In this paper, we review leading machine learning (ML) approaches and research directions in US, with an emphasis on recent ML advances. We also present our outlook on future opportunities for ML techniques to further improve clinical workflow and US-based disease diagnosis and characterization.