Quantitative Assessment of Liver Fibrosis: B1 Inhomogeneity-Corrected VFA T1 Mapping on Gadobenate Dimeglumine-Enhanced MRI

Introduction: Accurate early diagnosis and assessment of liver fibrosis are important for patient treatment and prognosis. This study explored the value of Gd- BOPTA-enhanced T1 mapping via the B1 inhomogeneity-corrected Variable Flip Angle (VFA) method for staging liver fibrosis in rats. Methods: Sprague‒Dawley rats were divided into one control group (n = 6) and four carbon tetrachloride-induced liver fibrosis groups (n = 6 each group). T1 mapping via B1 inhomogeneity-corrected VFA was performed before and 90 minutes after Gd-BOPTA administration. Precontrast T1 values (T1pre), postcontrast T1 values (T1post), and the reduction rate of T1 values (ΔT1%) were quantified on T1 mapping images. The diagnostic performance was evaluated by the Area Under the Receiver Operating Characteristic Curve (AUC). The correlations between T1pre, T1post, ΔT1% values, and the expression levels of hepatocyte transporters (Oatp1a1 and Mrp2) were evaluated. Results: T1post and ΔT1% were significantly correlated with liver fibrosis stage (r = 0.832, p <0.001; r = −0.798, p <0.001, respectively), whereas T1pre was not significantly correlated with fibrosis stage (r = 0.357, p = 0.062). The AUCs of T1post and ΔT1% were greater than those of postcontrast signal intensity for diagnosing stages F2–F4 (0.936, 0.941 vs. 0.791; p = 0.043, 0.038, respectively), F3–F4 (0.928, 0.861 vs. 0.660; p = 0.003, 0.028, respectively) and F4 (0.965, 0.896 vs. 0.761; p = 0.021, 0.049, respectively). Oatp1a1 and Mrp2 expression levels correlated significantly with T1post (r = −0.859, p = 0.001; r = −0.697, p = 0.017) and ΔT1% (r = 0.891, p <0.001; r = 0.685, p = 0.020), respectively. Discussion: T1post and ΔT1% were significantly correlated with liver fibrosis stages, and have good diagnostic performance for staging liver fibrosis. The protein expression levels of Oatp1a1 and Mrp2 correlated significantly with T1post and ΔT1%. Conclusion: Gd-BOPTA-enhanced T1 mapping via the B1 inhomogeneity-corrected VFA shows promise as a potentially accurate and reliable tool for quantifying liver fibrosis stages.