Bridging the 3D geometrical organisation of white matter pathways across anatomical length scales and species

Abstract

We used diffusion MRI and x-ray synchrotron imaging on monkey and mice brains to examine the organisation of fibre pathways in white matter across anatomical scales. We compared the structure in the corpus callosum and crossing fibre regions and investigated the differences in cuprizone-induced experimental demyelination mouse brains versus healthy controls. Our findings revealed common principles of fibre organisation in the two species; small axonal fasciculi and major bundles formed laminar structures with varying angles, according to the characteristics of major pathways. Individual axon fasciculi exhibited tortuous paths around obstacles like blood vessels, but in a manner independent of fibre complexity and demyelination. A quantitative analysis of tissue anisotropies and fibre orientation distributions gave consistent results for different anatomical length scales and modalities, while being dependent on the field-of-view. Our study emphasises the need to balance field-of-view and voxel size when characterising white matter features across anatomical length scales.