*SBRT in Hepatocellular Carcinoma DOI: http://dx.doi.org/10.5772/intechopen.109622*

are organ-specific contrasts in MRI, and these are mainly used in the diagnosis of focal hepatic lesions in which previous imaging tests have been inconclusive. The three agents that have been developed for this purpose are mangafodipir trisodium (Mn-DPDP), gadobenate dimeglumine (Gd-BOPTA), and gadoxetic acid (Gd-EOB-DTPA). Poorly differentiated HCC does not pick up these contrasts, but it has been described that some well-differentiated hepatocellular carcinoma may do so.

## *2.2.1 Image acquisition in hepatocellular carcinoma*

Because of its special behavior, CT contrast acquisition for hepatocellular carcinoma is somewhat different from other tumors. In the normal liver, hepatic irrigation is mainly by the portal vein and to a lesser extent by the hepatic artery. In the process of hepatocarcinogenesis, arterial vascularization predominates over portal vascularization. For this reason, the diagnosis of hepatocellular carcinoma is based on its vascular behavior and radiological studies are performed with contrast in arterial, portal, and late phases, in addition to alpha-fetoprotein levels and histological analysis.

The typical radiological characteristics of hepatocellular carcinoma in both CT and MRI in the dynamic study are contrast hyperenhancement in the arterial phase with early washout in the late phase, the latter phase being decisive for the diagnosis as it becomes hypodense/hypointense with respect to the normal liver parenchyma, presenting in some cases a pseudocapsule image. Another important characteristic of hepatocellular carcinoma is its internal mosaic appearance due to the presence of areas with different density in CT or heterogeneous signal in MRI that mainly appear in the postcontrast study.

Sometimes hepatocellular carcinoma can be hypovascular and show no arterial hypervascularization, in which case the portal and late phases are very important, where they remain hypodense/hypointense or even have atypical behavior with hyperenhancement in the arterial phase and absence of late washout [27].

The signal characteristics of hepatocellular carcinoma on MRI is variable. In T1-weighted sequences, about one-third are seen as hypointense lesions, one-third are isointense, and another third are hyperintense (due to hemorrhage or fatty degeneration). In T2-weighted sequences, the signal intensity is closely related to the degree of malignancy, and the higher the degree of malignancy the more hyperintense in T2. Sometimes, there may be hypointense areas in T2 sequences, related to the presence of a scar, old bleeding (hemosiderin), or necrosis. In cases in which the capsule is present, it is hypointense in T1 and hyperintense in the postcontrast study. Fat deposition is easy to demonstrate on MRI (up to 14%) using T1 sequences. Peritumoral edema corresponding to compressed liver parenchyma can be seen in approximately 20% of cases. In diffusion sequences, hepatocellular carcinoma shows signal hyperintensity, with low ADC values, which translates a diffusion restriction due to high cellularity.
