 Introduction/Background Chronic liver disease encompasses a variety of causes of chronic liver injury, including nonalcoholic fatty liver disease, hepatitis C, hepatitis B, alcohol-related liver disease, primary sclerosing cholangitis, autoimmune hepatitis, and others. These diseases can progress to hepatic fibrosis and cirrhosis, with associated complications of portal hypertension, gastrointestinal hemorrhage, refractory ascites, hepatic encephalopathy, and primary liver cancer [1- 3]. Liver disease accounts for approximately 2 million deaths per year worldwide, 1 million due to complications of cirrhosis and 1 million due to viral hepatitis and hepatocellular carcinoma. Cirrhosis and liver cancer account for 3.5% of all deaths worldwide [4]. In the United States, the leading cause of cirrhosis is hepatitis C, with approximately 1.3% of the population having chronic hepatitis C infection [1-3], and mortality related to cirrhosis and liver cancer is underestimated and may be increasing [5,6]. The progression of hepatic fibrosis to compensated cirrhosis to decompensated cirrhosis can be slow and clinically silent. Although the standard for diagnosis of hepatic fibrosis and cirrhosis is liver biopsy, this technique is costly, plagued by sampling errors, can be morbid, and is not well accepted for longitudinal disease monitoring [7,8]. Thus, accurate noninvasive methods are desperately needed for establishing and grading severity of liver fibrosis as well as monitoring disease progression or response to therapy. Although a variety of serum markers exist for this purpose, they are inaccurate for intermediate stages of fibrosis, and imaging by conventional ultrasound (US), CT, and MRI is frequently performed to assess for cirrhosis and its complications in this patient population [9]. More advanced techniques such as MR elastography and US have been shown to be more accurate than conventional morphological imaging methods and are gaining acceptance for these applications.
Chronic Liver Disease.  Introduction/Background Chronic liver disease encompasses a variety of causes of chronic liver injury, including nonalcoholic fatty liver disease, hepatitis C, hepatitis B, alcohol-related liver disease, primary sclerosing cholangitis, autoimmune hepatitis, and others. These diseases can progress to hepatic fibrosis and cirrhosis, with associated complications of portal hypertension, gastrointestinal hemorrhage, refractory ascites, hepatic encephalopathy, and primary liver cancer [1- 3]. Liver disease accounts for approximately 2 million deaths per year worldwide, 1 million due to complications of cirrhosis and 1 million due to viral hepatitis and hepatocellular carcinoma. Cirrhosis and liver cancer account for 3.5% of all deaths worldwide [4]. In the United States, the leading cause of cirrhosis is hepatitis C, with approximately 1.3% of the population having chronic hepatitis C infection [1-3], and mortality related to cirrhosis and liver cancer is underestimated and may be increasing [5,6]. The progression of hepatic fibrosis to compensated cirrhosis to decompensated cirrhosis can be slow and clinically silent. Although the standard for diagnosis of hepatic fibrosis and cirrhosis is liver biopsy, this technique is costly, plagued by sampling errors, can be morbid, and is not well accepted for longitudinal disease monitoring [7,8]. Thus, accurate noninvasive methods are desperately needed for establishing and grading severity of liver fibrosis as well as monitoring disease progression or response to therapy. Although a variety of serum markers exist for this purpose, they are inaccurate for intermediate stages of fibrosis, and imaging by conventional ultrasound (US), CT, and MRI is frequently performed to assess for cirrhosis and its complications in this patient population [9]. More advanced techniques such as MR elastography and US have been shown to be more accurate than conventional morphological imaging methods and are gaining acceptance for these applications.