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. 2016 Dec 1;33(23):2133-2146.
doi: 10.1089/neu.2015.4267. Epub 2016 May 18.

Abnormalities in Diffusional Kurtosis Metrics Related to Head Impact Exposure in a Season of High School Varsity Football

Elizabeth M Davenport  1   2 , Kalyna Apkarian  3 , Christopher T Whitlow  4   3   5 , Jillian E Urban  3   6 , Jens H Jensen  7 , Eliza Szuch  8 , Mark A Espeland  9 , Youngkyoo Jung  4   3   6 , Daryl A Rosenbaum  3 , Gerard A Gioia  10 , Alexander K Powers  11   12 , Joel D Stitzel  3   5   6 , Joseph A Maldjian  1   2
Affiliations

Abnormalities in Diffusional Kurtosis Metrics Related to Head Impact Exposure in a Season of High School Varsity Football

Elizabeth M Davenport et al. J Neurotrauma. .

Abstract

The purpose of this study was to determine whether the effects of cumulative head impacts during a season of high school football produce changes in diffusional kurtosis imaging (DKI) metrics in the absence of clinically diagnosed concussion. Subjects were recruited from a high school football team and were outfitted with the Head Impact Telemetry System (HITS) during all practices and games. Biomechanical head impact exposure metrics were calculated, including: total impacts, summed acceleration, and Risk Weighted Cumulative Exposure (RWE). Twenty-four players completed pre- and post-season magnetic resonance imaging, including DKI; players who experienced clinical concussion were excluded. Fourteen subjects completed pre- and post-season Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). DKI-derived metrics included mean kurtosis (MK), axial kurtosis (K axial), and radial kurtosis (K radial), and white matter modeling (WMM) parameters included axonal water fraction, tortuosity of the extra-axonal space, extra-axonal diffusivity (De axial and radial), and intra-axonal diffusivity (Da). These metrics were used to determine the total number of abnormal voxels, defined as 2 standard deviations above or below the group mean. Linear regression analysis revealed a statistically significant relationship between RWE combined probability (RWECP) and MK. Secondary analysis of other DKI-derived and WMM metrics demonstrated statistically significant linear relationships with RWECP after covariate adjustment. These results were compared with the results of DTI-derived metrics from the same imaging sessions in this exact same cohort. Several of the DKI-derived scalars (Da, MK, K axial, and K radial) explained more variance, compared with RWECP, suggesting that DKI may be more sensitive to subconcussive head impacts. No significant relationships between DKI-derived metrics and ImPACT measures were found. It is important to note that the pathological implications of these metrics are not well understood. In summary, we demonstrate a single season of high school football can produce DKI measurable changes in the absence of clinically diagnosed concussion.

Keywords: Head Impact Telemetry System; Risk Weighted Cumulative Exposure; concussion; diffusion kurtosis imaging; football.

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Figures

<b>FIG. 1.</b>
FIG. 1.
Risk Weighted Cumulative Exposure combined probability (RWECP) vs. abnormal linear anisotropy (CL) voxels in the white matter, adjusted for age, body mass index, and time between scans (R2 = 0.5626; p < 0.0001).
<b>FIG. 2.</b>
FIG. 2.
Risk Weighted Cumulative Exposure combined probability (RWECP) vs. abnormal kurtosis (K) mean voxels in the whole–brain, adjusted for age, body mass index, and time between scans (R2 = 0.6598; p < 0.0001).
<b>FIG. 3.</b>
FIG. 3.
Risk Weighted Cumulative Exposure combined probability (RWECP) vs. abnormal intra-axonal diffusivity (Da) voxels in white matter areas with fractional anisotropy (FA) >0.4, adjusted for age, body mass index, and time between scans (R2 = 0.6412; p < 0.0001).
See this image and copyright information in PMC

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