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

• DOI: 10.1089/neu.2015.4267
• Publication Date: 2016-04-04T11:42:02Z
• Authors: Elizabeth M. Dave...; Kalyna Apkarian; Christopher T. Wh...; Jillian E. Urban; Jens H. Jensen; Eliza Szuch; Mark A. Espeland; Youngkyoo Jung; Daryl A. Rosenbaum; Gerard A. Gioia; Alexander K. Powers; Joel D. Stitzel; Joseph A. Maldjian
• Keywords: Male; diffusion kurtosis imaging; football; Risk Weighted Cumulative Exposure; Neurology & Neurosurgery; Schools; Adolescent; 4. Education; Clinical Sciences; 0206 medical engineering; Neurosciences; Football; 02 engineering and technology; White Matter; 03 medical and health sciences; Diffusion Magnetic Resonance Imaging; 0302 clinical medicine; Clinical Research; Athletes; Head Impact Telemetry System; concussion; Biomedical Imaging; Humans; Seasons; Brain Concussion

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.