PurposeTo pathologically verify the correlation between native T-1 mapping, postcontrast T-1 mapping, and extracellular volume fraction (ECV) and myocardial diffuse fibrosis, as determined by collagen volume fraction (CVF). Materials and MethodsThirty New Zealand white rabbits were randomly divided into the control group (n = 6), diabetes 3 months group (n = 8), diabetes 6 months group (n = 8), and diabetes 9 months group (n = 8). All the rabbits underwent clinical 3.0T magnetic resonance (MR) examinations with pre- and postcontrast modified Look-Locker inversion recovery T-1 mapping. For the histological study, each rabbit was sacrificed after MR scanning, hematoxylin and eosin and Masson staining of the left ventricular myocardium were performed, and CVF was calculated. Pre- and postcontrast T-1 values and ECV were compared to CVF using Pearson's correlation coefficients. ResultsTwo rabbits died in each diabetes group, thus each group included six rabbits. ECV calculated from pre- and postcontrast T-1 values showed a very strong correlation with CVF (r = 0.876, P < 0.001), whereas postcontrast T-1 values exhibited a moderate correlation with CVF (r = -0.564, P = 0.004). In contrast, precontrast T-1 values showed no correlation with CVF (r = 0.311, P = 0.139). ConclusionECV has a very strong correlation with pathological CVF, and can be used to assess the degree of diffuse myocardial fibrosis better than the postcontrast T-1 value. Precontrast T-1 value has no significant correlation with diffuse myocardial fibrosis. J. Magn. Reson. Imaging 2016;44:1179-1185.