In daily practice, common indications for abdominal computed tomography (CT) include detection of liver malignancies, characterization of liver lesions suggested by other imaging tests, and evaluation of chronic liver diseases.Hepatocellular carcinoma (HCC) is the most common primary malignant hepatic neoplasm and its incidence is increasing. HCC accounts for 6% of all human cancers worldwide, being the fifth most common malignancy in men and the tenth in women . HCC usually occurs as a complication of chronic liver disease and most often arises in patients with hepatic cirrhosis. Imaging the cirrhotic liver is a technical challenge for CT.Cirrhosis alters the normal parenchyma with various degenerative processes such as fibrosis, scarring, and nodular regeneration.Not only are these tumors difficult to detect in patients with cirrhosis, but the alterations inherent in cirrhosis create lesions that may simulate a tumor.Most HCCs are hypervascular lesions that typically enhance during the phase of maximum hepatic arterial enhancement. Therefore, such lesions have often been difficult to detect with conventional CT of the liver, in which only portal venous-phase imaging was performed because of the long scanning time. During the past decade, the introduction of helical CT technology has opened the door to new approaches to liver imaging.With its short acquisition time, spiral CT allows imaging of the entire liver twice, before equilibrium: a hepatic arterial dominant phase and a portal venous phase of enhancement . Several studies have demonstrated that this biphasic approach to scanning greatly improves the detection of HCC (Fig. 1). Because of the vascular nature of these lesions, there is evidence that a greater number of HCC nodules are detected when images are acquired with dualphase CT compared with portal venous phase imaging alone [3, 4].
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