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, particularly with the use of contrast agents and a dynamic technique (1). With conventional CT, contrast material enhancement was performed either in incremental (predominantly reported in the United States) or single-level (reported in the Japanese and some European literature) dynamic 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 entire liver, which means that both detection and characterization of hepatis tumor(s) can be performed simultaneously (1,6,7). Thus, knowledge of the hemodynamics in both hepatic parenchyma and liver tumor becomes more important for proper characterization of liver tumor(s) and to avoid erroneous identification of pseudo-lesions as well (8,9). Nontumorous abnormalities, such as focal fat deposit and focal sparing of fatty infiltration, are clearly depicted on unenhanced CT and MR images and reportedly have a close relationship with blood flow (10,11). In this review article, we will discuss how blood flow can affect the appearance of both contrast material-enhanced and unenhanced CT and MR images.