Surface based analysis of diffusion orientation for identifying architectonic domains in the in vivo human cortex

Abstract

Diffusion tensor MRI is sensitive to the coherent structure of brain tissue and is commonly used to study large-scale white matter structure. Diffusion in grey matter is more isotropic, however, several groups have observed coherent patterns of diffusion anisotropy within the cerebral cortical grey matter. We extend the study of cortical diffusion anisotropy by relating it to the local coordinate system of the folded cerebral cortex. We use 1mm and sub-millimeter isotropic resolution diffusion imaging to perform a laminar analysis of the principal diffusion orientation, fractional anisotropy, mean diffusivity and partial volume effects. Data from 6 in vivo human subjects, a fixed human brain specimen and an anesthetized macaque were examined. Large regions of cortex show a radial diffusion orientation. In vivo human and macaque data displayed a sharp transition from radial to tangential diffusion orientation at the border between primary motor and somatosensory cortex, and some evidence of tangential diffusion in secondary somatosensory cortex and primary auditory cortex. Ex vivo diffusion imaging in a human tissue sample showed some tangential diffusion orientation in S1 but mostly radial diffusion orientations in both M1 and S1.

Diffusion tensor characteristics of gyrencephaly using high resolution diffusion MRI in vivo at 7T

“…The fibres in the cerebral cortex can now be investigated in vivo. Regional variation has been shown in the orientation of the principal eigenvector of the cortical diffusion tensor in primary sensory vs. motor cortices (McNab et al, 2013). In that study, it was also noted that the precentral and postcentral gyral crowns are characterized by tensors that are radial to the cortical surface at the grey-white matter boundary, while the banks show a more tangential orientation.…”

“…Therefore, bias might exist in the results towards fibre configurations dominant in these areas. In general, this raises the question about variability in cortical fibre configurations over regions, as has been demonstrated for primary motor vs. primary somatosensory cortex (McNab et al, 2013). One might speculate on the usefulness for segmentation of the cortical sheet.…”

“…Following McNab et al (2013), the sampled surfaces are referred to as surfaces, not layers. This is to avoid confusion with histological layers.…”

Interpolation of diffusion weighted imaging datasets

“…Our anatomical findings are in line with our previous work where DEC-FA maps of the fixed pig brain revealed the layered organisation in GM regions as in both the cerebral cortex and the hippocampus . Layered organisation of the living and fixated human brain has also been found with DTI in cerebral cortex (Leuze et al, 2012;McNab et al, 2013) and hippocampus (Shepherd et al, 2007). While Nissl staining revealed far much finer layer details than FA reflecting differences in cell density amongst layers, DEC-FA maps mainly provide information about structural orientation.…”

Anatomical accuracy of brain connections derived from diffusion MRI tractography is inherently limited

“…Granted, the use of animal models is somewhat limited because of interspecies differences in neuroanatomy (45,46). However, given the similarities in the connectivity profile between the monkey and human brain (47,48), macaque models will continue to serve as an indispensable tool for explicating general organizational principles of brain networks such as characterization of the directional transitions that axons make when entering or exiting gray matter (35,49,50). Insights from such studies may help improve the accuracy of tractography techniques.…”