The role of microvascular pathology in the development and progression of dementia is currently unclear. Non-invasive methods for imaging microvessel structure are needed to study cerebrovascular alterations in-vivo. The time for water molecules to change direction relative to the diffusion time alters the measured pseudo-diffusion coefficient of intra-voxel incoherent motion (IVIM). Using multi-diffusion time multi-b-value data and a velocity autocorrelation model, the capillary segment length (l) can estimated. In this study we validate hippocampal l against vascular corrosion casts, then apply the method to study vascular structure and function in a rat model of hypertension in comparison with age-matched controls.