Quantifying Longitudinal Microstructural Changes in Mild Traumatic Brain Injury Patients with Mean Apparent Propagator MRI.

Mean apparent propagator MRI (MAP-MRI) quantifies subtle alterations in tissue microstructure noninvasively and provides a more nuanced and comprehensive assessment of tissue architectural and structural integrity compared with other diffusion MRI techniques. We investigate the sensitivity of MAP-MRI-derived quantitative imaging biomarkers to detect previously unseen microstructural damage in patients with mild traumatic brain injuries (mTBI), whose clinical scans otherwise appeared normal. We developed and validated an MAP-MRI data processing pipeline for analyzing diffusion-weighted images for use in healthy controls and mTBI patients whose longitudinal scans were obtained from the GE/NFL/mTBI MRI database. A regional outlier analysis of longitudinal tissue changes in a pilot cohort during a 90-day period of observation showed that several MAP-MRI-derived parameters had increased intersession variability in white matter tracts and deep gray matter nuclei of mTBI patients relative to healthy controls. In summary, longitudinal monitoring of changes in MAP-MRI metrics may provide a comprehensive means to study pathological mTBI alterations that evolve at different timescales, while current image-based biomarkers lack the sensitivity and specificity and are unable to predict patient outcome.