Contrast agents for hepatic MRI.

Liver specific contrast media (LSCM) can be subdivided according to different modalities of hepatic distribution: exclusive distribution to the hepatocellular compartment can be obtained using CM which accumulate within the hepatocytes after slow infusion; other CM demonstrate combined perfusion and hepatocyte-selective properties, with an initial distribution to the vascular-interstitial compartment (in an analogous manner to that of the conventional extracellular CM), thereafter, a fraction of the injected dose is taken up into the hepatocytes causing an increase in the signal intensity of the hepatic tissue. The use of the superparamagnetic effect of iron oxide particles is based on distribution in the reticuloendothelial system (RES), usually well represented in the normal parenchyma as well as in benign hepatocellular lesions, and absent in most malignant lesions. It is necessary to have an in-depth knowledge of either the biological and histological characteristics of focal liver lesions (FLL) or the enhancement mechanism of LSCM to gain significant accuracy in the differential diagnosis of FLL. Dynamic contrast-enhanced MRI is an important tool in the identification and characterization of FLL. With LSCM it is possible to differentiate benign from malignant lesions and hepatocellular lesions from non hepatocellular lesions with high accuracy. To understand the contrast behaviour after injection of LSCM it is necessary to correlate the contrast enhancement with both the biological and histological findings of FLL.