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

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

doi:10.3389/fneur.2018.00575

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

Front Neurol. 2018 Aug 6:9:575. doi: 10.3389/fneur.2018.00575. eCollection 2018.

Authors

Alexander M Weber^{1

2}, Anna Pukropski³, Christian Kames^{2

4}, Michael Jarrett^{1

2}, Shiroy Dadachanji⁵, Jack Taunton⁵, David K B Li^{2

6

7}, Alexander Rauscher^{1

2

6}

Affiliations

¹ Division of Neurology, Department of Pediatrics, University of British Columbia, Vancouver, BC, Canada.
² UBC MRI Research Centre, University of British Columbia, Vancouver, BC, Canada.
³ Program of Cognitive Science, University of Osnabrueck, Osnabrueck, Germany.
⁴ Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada.
⁵ Division of Sports Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.
⁶ Department of Radiology, University of British Columbia, Vancouver, BC, Canada.
⁷ MS/MRI Research Group, University of British Columbia, Vancouver, BC, Canada.

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.

Keywords: axial diffusivity; concussion; diffusion tensor imaging; magnetic resonance imaging; myelin; quantitative susceptibility mapping; radial diffusivity; white matter.