BLOOD-FLOW AND LIVER IMAGING

With the advent of computed tomography (CT) and magnetic resonance (MR ) imaging, we have had greater opportunity to visualize the liver, par ticularly with the use of contrast agents and a dynamic technique (1). With conventional CT, contrast material enhancement was performed eit her in incremental (predominantly reported in the United States) or si ngle-level (reported in the Japanese and some European literature) dyn amic style (2-5). The introduction of helical CT and modern MR imaging has made it possible to obtain a multi-phase dynamic study of the ent ire liver, which means that both detection and characterization of hep atis tumor(s) can be performed simultaneously (1,6,7). Thus, knowledge of the hemodynamics in both hepatic parenchyma and liver tumor become s more important for proper characterization of liver tumor(s) and to avoid erroneous identification of pseudo-lesions as well (8,9). Nontum orous abnormalities, such as focal fat deposit and focal sparing of fa tty infiltration, are clearly depicted on unenhanced CT and MR images and reportedly have a close relationship with blood flow (10,11). In t his review article, we will discuss how blood flow can affect the appe arance of both contrast material-enhanced and unenhanced CT and MR ima ges.