Technical recommendations for MRI with EC agents and EC agents with modest HC uptake

• Pre-contrast, arterial phase, portal venous phase, and delayed phase required.Unenhanced T1w OP and IP required.
  • Late arterial phase strongly preferred over early arterial phase.
• T2w FSE or T2w SSFSE required.
• DWI suggested.
• Multi-planar acquisitions or reformations may be helpful.
• Post-processing with generation of subtraction images (arterial phase – pre; arterial phase – portal venous phase or arterial phase – delayed phase) may be helpful in select cases.
• Pre-contrast, arterial phase, portal venous phase, and delayed phase required for MRI per OPTN policy to assign HCC exception points.

Background

• Each phase (pre, arterial phase, portal venous phase, and delayed phase) contributes to characterization of LI-RADS major features with little additional examination time and, unlike CT, no additional radiation exposure.
• Late arterial phase is strongly preferred. HCC enhancement usually is greater in the late than in the early arterial phase. Some HCCs show hyper-enhancement only in the late arterial phase.
• OP/IP allows identification of fat and iron and is necessary for assessment of some LI-RADS ancillary features.
• If available, acquire using a dual-echo sequence rather than as separate single-echo acquisitions to ensure image co-registration across echoes.
• For dual-echo sequences, OP-then-IP design is preferable to IP-then-OP design because it permits more reliable evaluation of fat and iron.
• T2w improves distinction between solid vs. nonsolid and is necessary for assessment of some ancillary LI-RADS features.
• DWI may be useful for detection of focal observations and is necessary for assessment of restricted diffusion, but DWI is not as robust or widely available as other MRI sequences. Hence, DWI is suggested but not required.
• Multi-planar acquisitions or reformations may be helpful to differentiate mass from non-mass and to identify capsule appearance. They also may be used to measure observation diameter if they depict observation margins more clearly than axial images.

Potential pitfalls and challenges

• For observations that are hyper-intense pre-contrast, arterial phase – pre subtraction images may be helpful for evaluation of arterial phase enhancement. Also, for some observations, arterial phase – portal venous phase or arterial phase – delayed phase subtraction images may be helpful for evaluation of “washout”.
• For subtractions to be valid, source images need to be co-registered and acquired with the same technique.