Fig. 2. Illustration of the different length scales accessible by diffusion MRI in the brain.
Macrostructure refers to structures on the whole-brain and regional level, while microstructure refers to structures on the microscopic level, e.g., cells and axons. Mesostructure resides in the intermediate, millimeter to sub-millimeter regime, on the order of the typical MRI voxel size. Figure contents adapted from (Reisert et al., 2017).