Magnetic resonance imaging of hepatocellular carcinoma.

In hepatocellular carcinomas (HCCs), T(1) shortening occurs due to internal protein, fat, copper, iron, hypercellularity, or a combination thereof. T(1)-weighted magnetic resonance imaging (MRI) is obtained with a non-fat-suppressed phase shift [in- (4 ms) and opposed- (2 ms) phase] gradient-echo sequence. Internal fat deposition is often (36%) seen in well-differentiated HCCs between 1.1 and 1.5 cm in size. T(2)-weighted MRI is crucial in differentiating HCCs from premalignant or borderline lesions in cirrhosis and serves as a tie breaker for small early-enhancing lesions. Gadolinium-enhanced MRI has advantages over contrast-enhanced CT: greater contrast enhancement, smaller volume of contrast, and less frequent adverse reactions. Double hepatic arterial-phase imaging has been performed in many centers, allowing less frequent off-timing arterial-phase imaging and improved temporary resolution. Hypervascular HCCs often show 'corona' enhancement in the late hepatic arterial phase, which makes it possible to distinguish small HCCs from enhancing pseudolesions. Liposoluble gadolinium chelate (e.g., Gd-EOB-DTPA) behaving both as an extracellular and hepatobiliary agent is very useful in the diagnosis. Diffusion-weighted imaging has become a routine imaging tool thanks to the parallel imaging technique. However, diffusion-weighted imaging may not significantly improve detection, characterization, or estimation of tumor grade for HCCs, and it should still be supplementary. In summary, we believe MRI outperforms CT in the diagnosis of HCCs. Copyright 2008 S. Karger AG, Basel.