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. 2012 Feb;30(2):171-80.
doi: 10.1016/j.mri.2011.10.001. Epub 2011 Nov 12.

Subject-specific changes in brain white matter on diffusion tensor imaging after sports-related concussion

Jeffrey J Bazarian  1 , Tong Zhu, Brian Blyth, Allyson Borrino, Jianhui Zhong
Affiliations

Subject-specific changes in brain white matter on diffusion tensor imaging after sports-related concussion

Jeffrey J Bazarian et al. Magn Reson Imaging. 2012 Feb.

Abstract

Background and purpose: Current approaches to diffusion tensor imaging (DTI) analysis do not permit identification of individual-level changes in DTI indices. We investigated the ability of wild bootstrapping analysis to detect subject-specific changes in brain white matter (WM) before and after sports-related concussion.

Materials and methods: A prospective cohort study was performed in nine high school athletes engaged in hockey or football and six controls. Subjects underwent DTI pre- and postseason within a 3-month interval. One athlete was diagnosed with concussion (scanned within 72 h), and eight suffered between 26 and 399 subconcussive head blows. Fractional anisotropy (FA) and mean diffusivity (MD) were measured in each WM voxel. Bootstrap samples were generated, and a permuted t test was used to compare voxel-wise FA/MD changes in each subject pre- vs. postseason.

Results: The percentage of WM voxels with significant (p<.05) pre-post FA changes was highest for the concussion subject (3.2%), intermediary for those with subconcussive head blows (mean 1.05%±.15%) and lowest for controls (mean 0.28%±.01%). Similarly, the percentage of WM voxels with significant MD changes was highest for the concussion subject (3.44%), intermediary for those with subconcussive head blows (mean 1.48%±.17%) and lowest for controls (mean 0.48%±.05%). Significantly changed FA and MD voxels colocalized in the concussion subject to the right corona radiata and right inferior longitudinal fasciculus.

Conclusions: Wild bootstrap analysis detected significantly changed WM in a single concussed athlete. Athletes with multiple subconcussive head blows had significant changes in a percentage of their WM that was over three times higher than controls. Efforts to understand the significance of these WM changes and their relationship to head impact forces appear warranted.

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Figures

Figure 1
Figure 1
Total Change Ratios in FA and MD for Each Subject The number of voxels with significant pre-season to post-injury/season changes in FA and MD is quantified by the percent of all WM voxels with a significant change (either increased or decreased) in FA or MD. Change defined as (post-season)-(pre-season).
Figure 2
Figure 2
T-statistic Map from the WB-Permutation Test Permutation T-statistic maps of FA (middle row) and MD (bottom row) in the mild TBI athlete (A) and control subject 5 (B) are superimposed on the FA map. Red voxels represent a significant pre-season to post-season/injury increase, while green voxels represent a decrease. The transformed JHU WMPM is also superimposed on the FA map of the corresponding individuals (top row). Deep white matter structures are clearly labeled for identification of regions with significant FA/MD changes from pre- to post-season.
Figure 3
Figure 3
Directional Change Ratios in FA and MD for Each Subject The direction of changes in FA and MD from pre-season to post-injury/season are quantified by the ratio the number of significantly increased voxels over the number of significantly decreased voxels (FA+/FA- and MD+/MD-). Most subjects display increases in FA and decreases in MD.
Figure 4
Figure 4
Mean FA and MD values in ROIs with Significant Pre-season to Post-Injury/season Changes. Mean FA (A) and MD values (B) are displayed from voxels within ten WM structures in which the number of voxels with significantly increased FA or significant decreased MD from pre-season to post-season were among the largest within all 56 ROIs investigated for all athlete subjects. These structures are the right posterior thalamic radiata (PTR-R), the right uncinate fasciculus (UNC-R), the bilateral sagittal stratum (SS_L/R), including the inferior longitudinal fasciculus (ILF) and the inferior fronto-occipital fasciculus (IFOF), the bilateral body of corpus callosum (BCC-L/R), the bilateral retrolenticular part of internal capsule (RLIC-L/R), the right superior corona radiata (SCC-R) and the right cingulum near hippocampus (CGH-R).
Figure 5
Figure 5
Change in Cognitive Performance Pre-season to Post-Injury/season Changes in Pre-season to Post-Injury/season ImPACT test scores are displayed for the six controls (Control 1–6), the 8 athletes with sub-concussive head blows (Athlete 1–8), and the single mild TBI athlete (Athlete 9). Results are given in terms of mean percent change in score, where change defined as (post-season)-(pre-season). Whiskers represent the maximum and minimum value, the boundaries of the boxes are the 25th and 75th percentile value, and the line in the box is the 50th percentile (median) value.
Figure 6
Figure 6
Relationship of Head Hits and Post Concussive Symptoms to Changes in DTI Indices The number of self-reported head hits correlated strongly with the proportion of WM voxels showing significant changes in: a) FA (r=0.77, p=0.002) and b) MD (r=0.78, p=0.0016). Increases in post concussive symptom scores (post-season score – pre season score) over the study interval also correlated with the proportion of WM voxels showing significant changes in: c) FA (r=0.86, p=0.0002) and d) MD (r=0.80, p=0.0009). Negative post-pre scores indicate an improvement in post-concussive symptoms whereas positive post-pre scores indicate a worsening of symptoms. PC-post concussive.
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