Insights From Particle Simulations for Diffusion MRI Microstructure Studies

Diffusion MRI mostly involves quantification of how water diffuses in tissue, and its relationship with tissue microstructure. The technique promises great impact for soft tissue studies, since it provides a method of studying tissue microstructure based on millimetre-scale measurements. While multiple analytical models have been proposed to describe how water diffuses in tissue, specifically by simplifying cell structure and organisation, questions remain around the understanding and relevance of existing models. We performed simulations to provide insight into hindered and restricted tissue compartments, and how the diffusion process changes when inter-compartment exchange occurs. We consider distinct cases for modelled (spherical) cell size and diffusivity and describe the observations using the theory of diffusional retardation. Our observations may lead to new approaches for tissue microstructure imaging, and in parallel improve our understanding of the factors influencing the temporal dependence of diffusion and kurtosis.