The objective of this study was to characterize changes in head impact exposure (HIE) across multiple football seasons and to determine whether changes in HIE correlate with changes in imaging metrics in youth football players.

On-field head impact data and pre- and postseason imaging data, including those produced by diffusion tensor imaging (DTI), were collected from youth football athletes with at least two consecutive seasons of data. ANCOVA was used to evaluate HIE variations (number of impacts, peak linear and rotational accelerations, and risk-weighted cumulative exposure) by season number. DTI scalar metrics, including fractional anisotropy, mean diffusivity, and linear, planar, and spherical anisotropy coefficients, were evaluated. A control group was used to determine the number of abnormal white matter voxels, which were defined as 2 standard deviations above or below the control group mean. The difference in the number of abnormal voxels between consecutive seasons was computed for each scalar metric and athlete. Linear regression analyses were performed to evaluate relationships between changes in HIE metrics and changes in DTI scalar metrics.

There were 47 athletes with multiple consecutive seasons of HIE, and corresponding imaging data were available in a subsample (n = 19) of these. Increases and decreases in HIE metrics were observed among individual athletes from one season to the next, and no significant differences (all p > 0.05) in HIE metrics were observed by season number. Changes in the number of practice impacts, 50th percentile impacts per practice session, and 50th percentile impacts per session were significantly positively correlated with changes in abnormal voxels for all DTI metrics.

These results demonstrate a significant positive association between changes in HIE metrics and changes in the numbers of abnormal voxels between consecutive seasons of youth football. Reducing the number and frequency of head impacts, especially during practice sessions, may decrease the number of abnormal imaging findings from one season to the next in youth football.

本研究的目的是表征多个足球赛季头部撞击暴露 (HIE) 的变化，并确定 HIE 的变化是否与青年足球运动员的成像指标变化相关。

场上头部撞击数据和季前和季后成像数据，包括由弥散张量成像 (DTI) 产生的数据，是从至少连续两个赛季数据的青年足球运动员那里收集的。ANCOVA 用于按季节数评估 HIE 变化（冲击次数、峰值线性和旋转加速度以及风险加权累积暴露）。评估了 DTI 标量指标，包括分数各向异性、平均扩散率以及线性、平面和球面各向异性系数。对照组用于确定异常白质体素的数量，其定义为高于或低于对照组平均值的 2 个标准偏差。针对每个标量度量和运动员计算连续赛季之间异常体素数量的差异。

有 47 名运动员连续发生了多个 HIE 赛季，并且在其中的子样本 (n = 19) 中提供了相应的影像数据。从一个赛季到下一个赛季，在个别运动员中观察到 HIE 指标的增加和减少，并且没有观察到各个赛季 HIE 指标的显着差异（所有 p > 0.05）。对于所有 DTI 指标，练习影响次数、每次练习的第 50 个百分位数影响和每个会话的第 50 个百分位数影响的变化与异常体素的变化显着正相关。

这些结果表明，在青年足球连续赛季之间，HIE 指标的变化与异常体素数量的变化之间存在显着的正相关。减少头部撞击的次数和频率，尤其是在练习期间，可能会减少青年足球从一个赛季到下一个赛季的异常成像结果的数量。