ObjectiveTo detect diffuse myocardial fibrosis in different severity levels of left ventricular diastolic dysfunction (DD) in spontaneous type 2 diabetes mellitus (T2DM) rhesus monkeys.MethodsEighteen spontaneous T2DM and nine healthy monkeys were studied. Echocardiography was performed for diastolic function classification. Cardiac magnetic resonance (CMR) imaging was performed to obtain extracellular volume fraction (ECV) maps and T1 maps at two different spin-locking frequencies. ECV values, T1 values, and myocardial fibrosis index (mFI) values which are based on the dispersion of T1, were calculated. Global peak diastolic longitudinal strain rates (GSrL) were also obtained.ResultsEchocardiography results showed mild DD in nine T2DM monkeys and moderate DD in the other nine. The global ECV values were significantly different among healthy animals as compared with animals with mild DD or moderate DD, and the ECV values of animals with moderate DD were significantly higher as compared with those of mild DD. The mFI values increased progressively from healthy animals to those with mild DD and then to those with moderate DD. Diastolic function indicators (e.g., early diastolic mitral annulus velocity, GSrL) correlated well with ECV and mFI.ConclusionsMonkeys with T2DM exhibit increased ECV, T1, and mFI values, which may be indicative of the expansion of extracellular volume and the deposition of excessive collagen. T1 mapping may have the potential to be used for diffuse myocardial fibrosis assessment.Key Points center dot Monkeys with T2DM exhibit increased ECV, T1, and mFI values, which may be indicative of the expansion of extracellular volume and the deposition of excessive collagen.center dot The relationship between diastolic dysfunction and diffuse myocardial fibrosis may be demonstrated by imaging markers.center dot Non-contrast T1 mapping may have the potential to be used for diffuse myocardial assessment.