Lecture : The purpose of this lecture is to review the imaging techniques for liver imaging and characteristic imaging findings of common benign hepatic tumors. Ultrasonography (USG), the first-line imaging modality of the liver, is easy to perform, convenient and cheap. USG does not generate iodizing radiation and bedside examination is feasible. USG can be helpful to detect hepatic tumors and differentiate cystic and solid tumors. Doppler imaging and contrast-enhanced ultrasonography (CEUS) using inert gas bubbles are also helpful in evaluating vascularity of hepatic tumors. CT is the principal imaging tool for abdominal imaging and dynamic contrast enhanced CT images using iodine contrast agent can be very helpful to evaluate the vascularity, perfusion and shape of the tumors. MRI was thought to be the problem-solving tool for liver imaging, but now is the diagnostic imaging test of choice for characterizing liver tumors because of its superb soft tissue contrast and hepatocyte specific contrast agent. Hepatic cyst is the most common benign tumors of the liver. Hepatic cysts are anechoic on USG with thin, imperceptible walls and posterior enhancement. On CT, hepatic cysts are well-defined, homogenously low attenuated lesions. On MRI, T2 bright signal intensity, T1 hypointense lesion without enhancement is the typical findings of hepatic cysts. Hepatic hemangioma is another common benign hepatic tumor. On USG, most hemangiomas are homogeneously hyperechoic with mild posterior enhancement. On dynamic imaging of CT, CEUS and MRI, hemangiomas shows typical peripheral nodular pattern of enhancement with progressive centripetal fill-in on delayed images. Hemangiomas shows T2 bright signal on MRI, similar to hepatic cysts and bright signal intensity on T2 weighted image is a very strong imaging feature favoring benignity. Hepatic adenomas and focal nodular hyperplasia (FNH) are much less common tumors. They are most often seen in young women. Risk factors for adenomas are hepatic steatosis, oral contraceptive use, anabolic steroid and glycogen storage disease. Recently, hepatic adenomas are classified into four subtypes; HNF1α mutated, β-catenin mutated, inflammatory and unclassified subtypes. The β-catenin activation and to a lesser extent HNF1α subtypes of adenomas may have a risk of transformation to HCC. Adenomas are often shows hypervascualrity on arterial phase or heterogeneous attenuation on CT because of necrosis, fat and hemorrhage. They show heterogeneous signal on MRI also. Inflammatory subtype shows diffuse and homogeneous high signal on T2 weighted images. FNH is frequently hypervascular on arterial phase with persistent enhancement in delayed phase. T2 hypointense scar with delayed enhancement is another specific imaging feature of FNH. Hepatobiliary phase imaging using hepatocyte-specific contrast agent can be very helpful for differentiating FNH from adenoma. On hepatobiliary phase, FNH show prolonged enhancement compared to the surrounding liver parenchyma. Hepatic adenoma usually shows low or heterogeneous signal on hepatobiliary phase due to hemorrhage or necrosis. Central scar of FNH can be found in color Doppler US or CEUS. Hepatic angiomyolipoma is another hypervascular tumor that can mimic HCC. Successful diagnosis relies on identification of intratumoral fat. However, fat-poor angiomyolipoma is very difficult to diagnose without pathological examinations. Biliary cystadenoma is uncommon cystic tumor of the liver origingnating in the bile duct. Malignant transformation to cystadenocarcinoma is not uncommon. On CT, biliary cystadenoma is seen as multilocular cystic mass with enhancing septa. MR signal of biliary cystadenoma varies depending on the content of the fluid.