The role of MRI using liver-specific contrast agent in the assessment of focal liver lesion

Radiol Bras. 2014 Set/Out;47(5):VII–VIII In the last decade, magnetic resonance imaging (MRI) with the use of intravenous extracellular contrast agents (for example, Gd-DTPA and Gd-DOTA) has been recognized as the noninvasive diagnostic tool of choice in the evaluation of focal liver lesions thanks to the fact that it does not require ionizing radiation in association with its high spatial resolution and excellent tissue contrast; its capability to study the vascular behavior of the lesion and to detect the presence of fat component in the lesion, besides allowing the differentiation of intrinsic tissue characteristics such as relaxation time and distribution of water in the liver lesion as well as in the surrounding parenchyma. Such aspects, among others, have led MRI to be rated as a molecular imaging method. However, despite those unquestionable advantages, MRI presents some limitations related to the differentiation of certain focal liver lesions in cirrhotic patients, such as focal nodular hyperplasia (FNH) versus adenoma and dysplastic nodule versus hepatocellular carcinoma (HCC) whose imaging findings are similar to each other but require distinctive approaches. Liver-specific contrast agents have been introduced to overcome such limitations and, among others, gadoxetic acid (Gd-EOB-DTPA) that was recently made commercially available in Brazil, can be mentioned. Gadoxetic acid (or gadoxetate disodium) is a paramagnetic contrast agent whose enhancement effect is mediated by a linear ion complex formed by gadolinium and ethoxy benzyl-diethylenetriaminepentaacetatic acid (EOB-DTPA). Because of the lipophilic property of the EOB component (ethoxy benzyl) combined with the DTPA hydrophilic property, the gadoxetic acid shows a two-phase or two-compartmental distribution pattern, i.e., after injection, the agent distributes into the vessels and extracellular spaces during the dynamic phases of hepatic enhancement (arterial, portal and equilibrium phases) and later on shows progressive hepatocytes uptake and subsequent complete renal and hepatobiliary excretion in equivalent amount in cases where the liver and kidneys function is preserved. Because of such a characteristic, gadoxetic acid is considered to be a “mixed action” (extracellular and hepatobiliary) contrast agent. Thus, it provides not only information related to the extracellular enhancement during the dynamic phases of hepatic perfu-