New contrast agents for imaging the liver.

The contrast agents suited for hepatic imaging can be divided into nonspecific, extracellular space- (ECS) directed, reticuloendothelial system- (RES) selective, and hepatocyte-selective compounds. There is a wide variation in regard to biodistribution, pharmacokinetics, contrast behavior, and tissue specificity. The ECS contrast agents provide information on vascularization and perfusion similar to that of X-ray contrast agents. The RES- and hepatocyte-specific contrast agents offer more "functional" information that may enhance tissue characterization; however, the biology of the different hepatocellular and nonhepatocellular tumors is limiting the diagnostic efficacy of the tissue-specific compounds in many respects.