To compare T1 mapping on Gd-EOB-DTPA-enhanced 1.5T magnetic resonance imaging (MRI), aspartate aminotransferase-to-platelet ratio index (APRI) and fibrosis-4 (FIB-4) for evaluating the severity of liver fibrosis in patients with chronic viral hepatitis B.This retrospective study included 118 patients with chronic viral hepatitis B (mean age: 55 years old; 102 men and 16 women) who underwent gadoxetic acid-enhanced MRI including T1 mapping on a 1.5T scanner ( MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). T1 mapping using 2 flip angle method was performed before and 20min hepatobiliary phase (HBP) after injection of gadoxetic acid (Primovist, Bayer-Schering) with following parameters: repetition time/echo time = 4.38 ms/1.93 ms, flip angle = 2ºand 12º, FOV = 380~400×300~324mm², matrix = 216×288, slab thickness = 200 cm resulting in an interpolated section thickness of 5 mm. Liver fibrosis stage was histologically determined according to the METAVIR system: F0 (n=16), F1 (n=8), F2 (n=12), F3 (n=14) and F4 (n=68). ROIs were drawn on the homogenous area of the right liver lobe on the T1 maps, avoiding major vessels and bile ducts. Mean T1 relaxation times were measured and the reduction rate of the T1 relaxation time (D%) was calculated. Liver function tests and platelet counts were performed, the APRI and FIB-4 index were calculated using the corresponding formulas. The correlation between T1 relaxation times, APRI and FIB-4 index with fibrosis stage were calculated by Spearman's rank correlation coefficients. Areas under receiver operating characteristic (AUROC) curves for T1 relaxation times, APRI and FIB-4 index were compared to assess their diagnostic performances in identifying liver fibrosis. The mean of the T1 relaxation time (unenhanced, HBP, and D%) and the APRI and FIB-4 index are provided in Table 1. Unenhanced, HBP, D% of T1 relaxation times, the APRI and FIB-4 index showed significant correlations with liver fibrosis stages (rho: 0.27, 0.69, -0.48, 0.50, 0.48, respectively, P<0.05). The AUROC curves of unenhanced, HBP, D% of T1 relaxation time, the APRI and FIB-4 index for the diagnosis of no (F=0), mild (F≤1), significant (F≥2), advanced fibrosis(F≥3) and cirrhosis (F＝4) are shown in the Figs 1. The AUROC for HBP T1 relaxation time prediction of significant fibrosis was significantly greater than that of FIB-4 (P=0.02), and the AUROC for HBP T1 relaxation time identification of advanced fibrosis was significantly greater than unenhanced, D% of T1 relaxation times, APRI and FIB-4 index(P＜0.01).Gadoxetic acid is a liver-specific MR imaging contrast agent with combined perfusion and hepatocyte-selective properties. After intravenous injection, gadoxetate disodium is gradually taken up by hepatocytes and eventually is excreted via the biliary pathway¹. Gd-EOB-DTPA has a T1-shortening effect, measurement of the T1 relaxation time of liver parenchyma before and after Gd-EOB-DTPA administration allows quantitative evaluation of liver function, Child-Pugh scores, necroinflammatory activity grades and hepatic fibrosis stages^2,3. Aspartate aminotransferase-to-platelet ratio index (APRI) and fibrosis-4 (FIB-4) are widely used simple and non-invasive tests that assess liver fibrosis. However, reliability decreases when patients have normal serum AST levels⁴.Unenhanced, HBP, D% of T1 relaxation times, the APRI and FIB-4 index are correlated to the stage of liver fibrosis. The HBP T1 relaxation time with gadoxetic acid-enhanced appears superior to unenhanced, D% of T1 relaxation times, the APRI and FIB-4 index in discriminating advanced liver fibrosis.