We report the development of a novel in-silico modelling framework for probing the in-vivo diffusion MRI signal in tumours, based on high-resolution (5-10µm) optical imaging data from complete tumours. Blood flow in tissue substrates was estimated using fluid dynamical modelling. We then simulated the MRI signal using a Monte Carlo approach, and fitted the VERDICT model. VERDICT has previously been proposed as a method to noninvasively quantify histological features of tissue, including intracellular, extracellular and vascular volume fractions, cell radius and blood flow. We report preliminary findings of a good correspondence between the ground truth and measured values.