Diffusion MRI with microstructure modeling can nominally map voxelwised cell radii and relative cell volume fractions for the entire tumour. This work proposes a model selection method that chooses the most suitable diffusion model among the two microstructural models and the monoexponential ADC model. This technique can potentially distinguish tissue microstructure featuring one or two underlying cell populations, and acellular necrosis. Microstructural parameters were also reliably estimated. These observations suggest the possible differentiation of three tumour microenvironments resulting from cancer therapy.