The Influence of Macroscopic and Microscopic Fibre Orientation Dispersion on Diffusion MR Measurements: A Monte-Carlo Simulation Study

Tingting Wang¹, Hui Zhang¹, Matt G. Hall¹, Daniel C. Alexander¹

Two classes of fibre orientation dispersion are observed in biological tissue: 1) Macroscopic dispersion, a population of straight fibres with different orientation, e.g. crossing and fanning fibres. 2) Microscopic dispersion, individual fibres with varying orientation, e.g. undulating fibres. Current reconstruction techniques implicitly assume macroscopic dispersion. Here we construct virtual tissue environments and conduct Monte-Carlo simulations to study differences that arise in the water dispersion, FA, and parameter estimates from biophysical models. Our results suggest that, the ODF can be recovered accurately in macroscopic dispersion, but not with small scale microscopic dispersion. We suggest considering such effects in future modelling works.