LI-RADS (Liver Imaging Reporting and Data System) is both a set of standardized terminology and a classification system for imaging findings in liver lesions. The LI-RADS score for a liver lesion is an indication of its relative risk for hepatocellular carcinoma (HCC). The classification system is meant to be used in livers which have risk factors for HCC (e.g. cirrhotic livers).
The original LI-RADS was developed for extracellular gadolinium contrast agents (e.g. Gadavist). Using a hepatobiliary contrast agent (e.g. Eovist/Primovist, MultiHance) changes the evaluation of hepatic lesions.
Five phases are often used for evaluation:
- T1W precontrast
- late arterial (30-35 sec)
- portal venous (~75 sec)
- "transitional" (~3 min)
- hepatobiliary (~20 min with Eovist/Primovist)
Assessment of hepatobiliary phase
The first important step is to evaluate the quality of the hepatobiliary phase. If the hepatic parenchyma is hyperintense relative to the blood pool, the phase can be considered adequate.
Although the hepatobiliary phase is usually acquired at 15-20 minutes for Eovist/Primovist (or 1 hour for MultiHance), severely cirrhotic livers may require a longer time (e.g. 30 minutes for Eovist/Primovist) to generate adequate images.
If the lesion is:
- hyperintense: indeterminate, and it could be either
- isointense: an ancillary feature that favors benignity
- hypointense: an ancillary feature that favors malignancy (cannot upgrade lesion past LR4)
- hepatobiliary phase hypointensity is not "washout"
- "washout" may be problematic to evaluate because the signal intensity of the liver is changing over time, relative to the lesion
- "washout" during the portal venous phase is reliable
- "washout" during the transitional stage is less reliable
- Eovist/Primovist has been associated with transient tachypnea during imaging in some patients (~15%)
- this may render the arterial phase suboptimal, making the important evaluation of hypervascularity suboptimal
- the capsule around some HCCs may be more difficult to identify
- a small percentage of HCC demonstrate Eovist/Primovist uptake
- hepatobiliary contrast reduces the ability to identify portal vein thrombus
- infiltrative HCC may be harder to visualize than with extracellular contrast agents
- Eovist/Primovist is not accurate at delineating the margins of TACE or RF ablation cavities
- some hepatic lesions (such as hepatic hemangiomas) may be more difficult to evaluate with hepatobiliary imaging than with extracellular imaging