Contrast agents for MR imaging of the liver

The evolution of contrast agents for MR imaging of the liver has proceeded along several different paths with the common goal of improving liver-lesion contrast. These contrast agents are used to accentuate the inherent differences in liver-lesion signal intensity through differential enhancement of proton relaxation within adjacent tissues. Contrast agents used for hepatic MR imaging can be broadly categorized into those that target the extracellular space, the hepatobiliary system, and the reticuloendothelial system. Although only a small number of liver contrast agents are currently available, others are rapidly proceeding through clinical trials and may soon be added to our clinical armamentarium. This article will briefly review the current clinical experience with these agents, discussing their mechanism of contrast enhancement, pharmacokinetics, and efficacy in the evaluation of focal liver lesions.