Since the hepatic artery and portal venous system supply approximately 20% and 80% of the hepatic blood supply, respectively, the earlier (hepatic arterial phase) images provide optimal lesion conspicuity for hypervascular lesions and the portal venous phase images are useful for hypovascular lesions (most metastatic lesions are relatively hypovascular and are better demonstrated during the portal venous phase, manifesting as areas of lower signal intensity compared with the markedly enhanced liver).