## 1 Introduction  
Chronic liver disease is a worldwide health problem and increases the risk of hepatic complications such as hepatocellular carcinoma (HCC) and liver failure [1]. Cirrhosis of the liver is a late stage of progressive liver disease defined as structural distortion of the entire liver by fibrosis and parenchymal nodules. The assessment of cirrhosis and chronic hepatitis highly depends on the degree of hepatic fibrosis, which is regarded as an important predictive indicator of cirrhosis [2]. As HCC is one of the most common malignancies in patients affected by these diseases [3], early detection and accurate staging of cirrhosis is an important issue in practical radiology. Generally, fibrosis is interpreted on Computed Tomography (CT) or magnetic resonance imaging (MRI) images by referring to changes in hepatic morphology, texture pattern, and the degree of liver stiffness. Although there is no effective treatment for decompensate or advanced cirrhosis, appropriate treatment such as interferon therapy is sometimes beneficial for early cirrhosis associated with viral hepatitis because fibrosis is potentially a reversible process in the early stages. Liver biopsy, which is an effective way of measuring changes in fibrosis staging, is regarded as the gold standard for assessing, by referring to the micrograph of a liver core needle biopsy, the severity of -liver disease and monitoring treatment. However, it is an invasive procedure, and significant bleeding occurs in 1-2 out of 100 patients, and it is possible to cause pain in 30-40% of cases, pneumothorax (3%), or even death (2/10,000) [4; 5]. The accuracy may also be questioned because of side effects, punctured sampling, and interobserver variability in the determination of semiquantitative fibrosis scores [6; 7; 8]. In order to decrease the need of painful biopsies, non-invasive tests using MR and ultrasound modalities have been widely used with the development of high-speed imaging devices. Recently, radiological assessments of hepatic fibrosis by magnetic resonance elastography (MRE) [8; 9; 10], gadolinium- or superparamagnetic iron-oxide-enhanced MR imaging [11; 12], diffusion-weighted MR imaging [13], and real-time ultrasonicographic elastography [14] have been reported. [PERSON] et al. [15] proposed a real-time elastography for diffuse histological lesions, showing a new and promising quantitative technology for assessing liver fibrosis in patients with chronic hepatitis B using a solography-based non-invasive method. Although such new imaging technologies have greatly impacted the traditional diagnostic methods, the interpretation of the numerous diseases from different types of medical images is a tough work, especially for the inexperienced residents or general radiologists. In the last decade, different types of computer-aided detection/diagnosis (CAD) systems have been developed to ease the workload of radiologists. Some CAD systems for quantitative assessment of liver fibrosis have been shown their promising results by analyzing morphology changes [16; 17] and the texture pattern of fibrosis [18] on CT/MR images. Recently, the degree of stiffness has also been analyzed through MR elastography. [PERSON] et al. [8] first proposed the method of MRE by direct visualization of propagating acoustic strain waves, and [PERSON] et al. [9] then proved its usefulness. However, both ultrasonicographic elastography and the above-mentioned MRE methods require special equipment, which limits their application in many hospitals. The fibrogenic change in stiffness of the liver from soft to hard indicates a change in the liver status from normal to chronic hepatitis, to cirrhosis, and even to liver cancer. However, obtaining the physical properties of the liver, such as tissue stiffness, is not possible with traditional MR imaging technology.