LI-RADS (Liver)

“[Focal perfusion alterations] are areas of arterial phase hyperenhancement most frequently caused by nontumorous arterioportal shunts or focal obstruction of a parenchymal portal vein branch. These alterations are usually peripheral, wedge shaped, and isointense relative to the surrounding parenchyma on T1- and T2-weighted MR images, and can be confidently characterized as LR-1; however, perfusion alterations can occasionally be nodular in contour and difficult to distinguish from a true enhancing lesion. Areas of nodular arterial phase hyperenhancement seen exclusively during the arterial phase are more appropriately categorized as LR-2, but if corresponding abnormalities (eg, increased T2 signal) can be seen on unenhanced images or with other sequences, perfusion alterations are considered unlikely, and the observation should be categorized as either LR-3 or LR-4 depending on its size and nonvascular features.”