Pathological Insights From Quantitative Susceptibility Mapping and Diffusion Tensor Imaging in Ice Hockey Players Pre and Post-concussion.

Alexander M Weber,Michael Jarrett,Alexander Rauscher,Christian Kames,Jack Taunton,Anna Pukropski,David K B Li,Shiroy Dadachanji

doi:10.3389/fneur.2018.00575

Abstract

Myelin sensitive MRI techniques, such as diffusion tensor imaging and myelin water imaging, have previously been used to reveal changes in myelin after sports-related concussions. What is not clear from these studies, however, is how myelin is affected: whether it becomes degraded and possibly removed, or whether the myelin sheath loosens and becomes “decompacted”. Previously, our team revealed myelin specific changes in ice hockey players 2 weeks post-concussion using myelin water imaging. In that study, 45 subjects underwent a pre-season baseline scan, 11 of which sustained a concussion during play and received follow-up scans: eight were scanned within 3 days, 10 were scanned at 14 days, and nine were scanned at 60 days. In the current retrospective analysis, we used quantitative susceptibility mapping, along with the diffusion tensor imaging measures axial diffusivity and radial diffusivity, to investigate this myelin disruption. If sports-related concussive hits lead to myelin fragmentation in regions of lowered MWF, this should result in a measurable increase in magnetic susceptibility, due to the anisotropic myelin fragmenting into isotropic myelin debris, and the diamagnetic myelin tissue being removed, while no such changes should be expected if the myelin sheath simply loosens and becomes decompacted. An increase in radial diffusivity would likewise reveal myelin fragmentation, as myelin sheaths block water diffusion out of the axon, with little to no changes expected for myelin sheath loosening. Statistical analysis of the same voxels-of-interest that were found to have reduced myelin water fraction 2 weeks post-concussion, revealed no statistically significant changes in magnetic susceptibility, axial diffusivity, or radial diffusivity at any time-point post-concussion. This suggests that myelin water fraction changes are likely due to a loosening of the myelin sheath structure, as opposed to fragmentation and removal of myelin debris.

Highlights

Concussions are the most common form of traumatic brain damage, with between 1.6 and 3.8 million injuries per year in the United States alone [1]
This study used measurements of white matter (WM) magnetic susceptibility along with DTI measures axial diffusivity (AD) and radial diffusivity (RD) to examine the impacts of concussion on the brain of varsity ice hockey players
Another study by Donovan et al demonstrated that repeated mTBI in rats leads to a spectrum of changes, including separation of the myelin sheath from the axon, decompaction of the myelin sheath, and fragmentation of the myelin sheath [23]

Summary

Introduction

Concussions are the most common form of traumatic brain damage, with between 1.6 and 3.8 million injuries per year in the United States alone [1] Despite how common they are, the underlying pathophysiological changes that take place after injury are poorly understood. Diffusion MRI, such as diffusion weighted imaging, diffusion tensor imaging, and diffusion kurtosis imaging, looks at the restriction of water diffusion to measure microstructural changes These methods hold promise in traumatic brain injury (TBI) research due their sensitivity to microstructural changes in white matter (WM), such as axonal injury using axial diffusivity or myelin damage using radial diffusivity [2,3,4], but often times lack tissue specificity

Methods

Results

Conclusion