Differential and correlational tractography as tract-based biomarkers in mild traumatic brain injury: A longitudinal MRI study.

We evaluated the fiber bundles in mild traumatic brain injury (mTBI) patients using differential and correlational tractography in a longitudinal analysis. Diffusion MRI data were acquired in 34 mTBI patients at 7 days (acute stage) and 3 months or longer (chronic stage) after mTBI. Trail Making Test A (TMT-A) and Digital Symbol Substitution Test changes were used to evaluate the cognitive performance. Longitudinal correlational tractography showed decreased anisotropy in the corpus callosum during the chronic mTBI stage. The changes in anisotropy in the corpus callosum were significantly correlated with the changes in TMT-A (false discovery rate [FDR] = 0.000094). Individual longitudinal differential tractography found that anisotropy decreased in the corpus callosum in 30 mTBI patients. Group cross-sectional differential tractography found that anisotropy increased (FDR = 0.02) in white matter in the acute mTBI patients, while no changes occurred in the chronic mTBI patients. Our study confirms the feasibility of using correlational and differential tractography as tract-based monitoring biomarkers to evaluate the disease progress of mTBI, and indicates that normalized quantitative anisotropy could be used as a biomarker to monitor the injury and/or repairs of white matter in individual mTBI patients.