Background Early detection and grading of liver inflammation are important for the management of nonalcoholic fatty liver disease (NAFLD) patients. There is still lack of a noninvasive way for the inflammation characterization in NAFLD. Purpose To assess liver inflammation grades by water specific T1 (wT1) in a rat model. Study Type Prospective. Animal model A total of 65 male rats with methionine‐choline‐deficient diet‐induced NAFLD and 15 male normal rats as control. Field Strength/Sequence A 3 T; multiecho variable flip angle gradient echo sequence. Assessment The wT1 and proton density fat fraction were quantified. Inflammation and fibrosis were assessed histologically with H&E and Sirius red stained slices according to the nonalcoholic steatohepatitis scoring system. Inflammation grade was scored with G0/G1/G2/G3 as none/mild/moderate/severe inflammation in NALFD rats. G0 + G1 and G2 + G3 were combined as none‐to‐mild grade (GL) and moderate‐to‐severe grade (GH) inflammation groups. Statistical Tests Analysis of variance (ANOVA), Mann–Whitney U test, Spearman's correlation, and receiver operating characteristic (ROC) analysis were performed. The areas under ROC (AUROC) was used for the diagnostic performance of wT1 in discriminating GH and GL. A P value < 0.01 was considered statistically significant. Results Seventy‐six rats were included in the analysis. The numbers in G0–G3 groups were 5, 16, 13, and 27. wT1 of G0–G3 was 568.55 ± 63.93 msec, 582.53 ± 62.98 msec, 521.21 ± 67.31 msec, and 508.79 ± 60.53 msec. A moderate but significant negative correlation between wT1 and histopathological inflammation grades was observed (rs = −0.42). The wT1 of GH (512.80 ± 62.22 msec) was significantly lower than GL (579.20 ± 61.89 msec). The AUROC of wT1 was 0.79, and the optimal cut‐off of wT1 was 562.64 msec (sensitivity: 90%, specificity: 76%), for the discrimination of GL and GH. Data Conclusions wT1 could differentiate none‐to‐mild inflammation from moderate‐to‐severe inflammation in the early stage of the NAFLD rat model. Evidence Level 1 Technical Efficacy Stage 1

Detection of inflammation is important to the NAFLD patients. Liver biopsy is limited by the sampling error. T1 quantification from MRI is believed to be one of promising imaging method to detect inflammation. However, intracellular hepatocyte lipid is a confounding factor for the accurate T1 quantitation in the case of the NAFLD. This study established a variable flip-angle multi-echo GRE sequence to produce the T1 value of water component (wT1) in a NAFLD rat model who underwent biopsy. The results indicate that wT1 could discriminate between moderate and severe inflammation stages (G2 +G3) from the no and mild stages (G0+G1).