A multi-modal application of magnetic resonance imaging (MRI) techniques to identify and quantify brain abnormalities in retired professional football players

Abstract

High contact sports put athletes at a higher risk of sustaining a concussion. This work focused on assessing regional brain health in aging, retired Canadian Football League (rCFL) players years to decades after retirement. Advanced, quantitative magnetic resonance imaging (MRI) techniques were implemented to identify and quantify microstructural brain white matter damage, cognitive functional signal characteristics (fractal dimension (FD) and amplitude of low frequency fluctuations (ALFF) and fractional ALFF (fALFF)), and cerebral blood flow (CBF) dysregulation. Due to the high reproducibility of diffusion tensor imaging (DTI) and resting state functional MRI (rsfMRI), a Z-scoring approach exploring outliers relative to a large normative dataset was implemented to examine each rCFL subject individually. However, arterial spin labelling (ASL) data is more sensitive to scanner inconsistencies, therefore a group-wise analysis was performed with the CBF and ASL spatial coefficient of variance (ASL sCoV) data. Minimal microstructural damage was detected in the rCFL subjects, but a substantial amount of functional and CBF abnormalities were present. The FD was significantly reduced in 48 of 91 regions-of-interest (ROIs) examined, and the four rCFL subjects with the highest number of abnormal ROIs all exhibited worse motor speed, social functioning and general health scores than the other rCFL subjects. Furthermore, the ALFF analysis identified the cerebellum, parietal lobe ROIs, and central sub-cortical ROIs to be consistently abnormal. Finally, the temporal occipital fusiform cortex, superior parietal gyrus, caudate nucleus, and the cerebellum were significantly abnormal bilaterally based on CBF and ASL sCoV values, which also correlated with worse physical functioning and elevated daily chronic pain. This work adds to the growing literature that brain changes are present later in life that may be related to concussions and repetitive sub-concussive head impacts sustained years earlier. Several consistently damaged ROIs also correlated with adverse clinical presentations to indicate areas of future research.