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Objectives: The current LR-5 criteria of Liver Imaging Reporting and Data System (LI-RADS) determined by only major features provide high specificity, but unsatisfactorily low sensitivity for the noninvasive diagnosis of hepatocellular carcinoma (HCC). This study aimed to identify significant ancillary features (AFs) in LI-RADS version 2018 and develop the upgraded LR-5 criteria to improve diagnostic performance on gadoxetic acid–enhanced magnetic resonance imaging (MRI). Methods: This retrospective study included 280 patients (366 observations including 281 HCCs) at high-risk for HCC who underwent gadoxetic acid–enhanced MRI between 2015 and 2017. Two readers evaluated major features and AFs for each observation and assigned a LI-RADS category. Independently significant AFs were identified through logistic regression analysis. Upgraded LR-5 criteria were developed by combining independently significant AFs with LR-4 assigned by major features alone. Sensitivities and specificities of the diagnostic criteria were compared using McNemar's test. Results: Two of the AFs favoring malignancy in general (mild-moderate T2 hyperintensity and hepatobiliary phase hypointensity) and two of the AFs favoring HCC in particular (nonenhancing "capsule" and mosaic architecture) were independently significant features for diagnosing HCC. By using the upgraded LR-5 criteria (LR-4 by major features alone + each aforementioned AF), sensitivities were significantly increased (69.4–76.9%) compared with the standard LR-5 (66.2%; all, p ≤ 0.004), whereas specificities (95.3–96.5%) were not significantly different (96.5%; all, p > 0.999). Conclusions: Independently significant AFs may be used to upgrade from LR-4 to LR-5 to improve sensitivity without impairing specificity on gadoxetic acid–enhanced MRI. Key Points: • Independently significant AFs for HCC on gadoxetic acid–enhanced MRI were mild-moderate T2 hyperintensity, hepatobiliary phase hypointensity, nonenhancing "capsule," and mosaic architecture. • When LR-4 criteria by major features alone in combination with significant AFs were upgraded to LR-5, sensitivities were higher than the standard LR-5, without impairing specificity. • Independently significant ancillary features in Liver Imaging Reporting and Data System version 2018 may be used to upgrade from LR-4 to LR-5 to improve sensitivity without impairing specificity on gadoxetic acid–enhanced MRI. [ABSTRACT FROM AUTHOR]