Longitudinal evolution of CT and MRI LI-RADS v2014 category 1, 2, 3, and 4 observations.

• While the majority of LR-2 observations remain stable over long-term follow-up, LR-3 and especially LR-4 observations have a higher risk for category progression. • Category transitions between sequential exams using different modalities (CT vs. MRI) may reflect modality differences rather than biological change. MRI, especially with the same type of contrast agent, may provide the most reproducible categorization, although this needs additional validation. • In a clinical practice setting, in which radiologists refer to prior imaging and reports, there was no significant association between changes in radiologist and changes in LI-RADS categorization.