• Nan-Jie Gong, Samuel Kuzminski, Michael Clark, Melissa Fraser, Mark Sundman, Kevin Guskiewicz, Jeffrey R Petrella, and Chunlei Liu.
• Electrical Engineering and Computer Sciences, University of California, Berkeley; Brain Imaging and Analysis Center, Duke University School of Medicine, United States. Electronic address: nanjie.gong@gmail.com.
• Neurobiol. Dis. 2018 Nov 1; 119: 79-87.

ObjectivesTo probe microstructural changes that are associated with subconcussive head impact exposure in deep and cortical gray matter of high school football players over a single season.MethodsPlayers underwent diffusion kurtosis imaging (DKI) and quantitative susceptibility mapping (QSM) scans. Head impact data was recorded. Association between parametric changes and frequency of frontal head impact was assessed.ResultsIn deep gray matter, significant decreases in mean kurtosis (MK) and increases in mean diffusivity (MD) over the season were observed in the thalamus and putamen. Correlations between changes in DKI metrics and frequency of frontal impacts were observed in the putamen and caudate. In cortical gray matter, decreases in MK were observed in regions including the pars triangularis and inferior parietal. In addition, increases in MD were observed in the rostral middle frontal cortices. Negative correlations between MK and frequency of frontal impacts were observed in the posterior part of the brain including the pericalcarine, lingual and middle temporal cortices. Magnetic susceptibility values exhibited no significant difference or correlation, suggesting these diffusion changes common within the group may not be associated with iron-related mechanisms.ConclusionMicrostructural alterations over the season and correlations with head impacts were captured by DKI metrics, which suggested that DKI imaging of gray matter may yield valuable biomarkers for evaluating brain injuries associated with subconcussive head impact. Findings of associations between frontal impacts and changes in posterior cortical gray matter also indicated that contrecoup injury rather than coup injury might be the dominant mechanism underlying the observed microstructural alterations.Advances In KnowledgeSignificant microstructural changes, as reflected by DKI metrics, in cortical gray matter such as the rostral middle frontal cortices, and in deep gray matter such as the thalamus were observed in high school football players over the course of a single season without clinically diagnosed concussion. QSM showed no evidence of iron-related changes in the observed subconcussive brain injuries. The detected microstructural changes in cortical and deep gray matter correlated with frequency of subconcussive head impacts.Implications For Patient CareDKI may yield valuable biomarkers for evaluating the severity of brain injuries associated with subconcussive head impacts in contact sport athletes.Copyright © 2018 Elsevier Inc. All rights reserved.

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