Liver-specific MR contrast agents: current status and prospects

Liver-specific MR contrast agents include superparamagnetic iron oxide (SPIO) particles and hepatobiliary paramagnetic agents. SPIO particles are phagocytosed by reticuloendothelial cells in the liver, resulting in negative enhancement of the liver parenchyma on T2- or T2*-weighted images. Ferumoxides and related iron oxide formulations have been tested clinically throughout the world, and have been demonstrated to improve the detection and characterization of hepatic neoplasms. Hepatobiliary paramagnetic agents are partially taken up by hepatocytes, yielding positive, sustained enhancement of the liver parenchyma on T1-weighted images. These agents are referred to as "value-added" versions of extracellular gadolinium compounds because they increase tumor-liver contrast in both the perfusion phase and hepatobiliary phase. Although only ferumoxides are currently available for clinical use, many agents are in the pipeline. The possibility of "one-stop shopping" diagnosis by liver-specific MR contrast agents is an attractive alternative to the existing multistep diagnosis in liver imaging. Further studies to analyze the cost-benefit ratio will follow, to determine whether liver-specific MR contrast agents lead to change in patient treatment and whether such a decision would be reliable.