Individualised Profiling of White Matter Organisation in Moderate-to-Severe Traumatic Brain Injury Patients Using TractLearn: A Proof-of-Concept Study

Approximately 65% of moderate-to-severe traumatic brain injury (m-sTBI) patients present with poor long-term behavioural outcomes, which can significantly impair activities of daily living. Numerous diffusion-weighted MRI studies have linked these poor outcomes to decreased white matter integrity of several commissural tracts, association fibres and projection fibres in the brain. However, these studies focused on group-based analyses, which are unable to deal with the substantial between-patient heterogeneity in m-sTBI. As a result, there is increasing interest in conducting individualised neuroimaging analyses. Here, we generated a detailed subject-specific characterisation of microstructural organisation of white matter tracts in 5 chronic patients with m-sTBI (29 - 49y, 2 females). We developed an imaging analysis framework using fixel-based analysis and TractLearn to determine whether the values of fibre density of white matter tracts at the individual patient level deviate from the healthy control group (n = 12, 8F, Mage=35.7y, age range 25 - 64y). Our individualised analysis confirmed unique white matter profiles, and the heterogeneous nature of m-sTBI to properly characterise the extent of brain abnormality. Future studies incorporating clinical data, as well as utilising larger reference samples and examining the test-retest reliability of the fixel-wise metrics are warranted. This proof-of-concept study suggests that these resulting individual profiles may assist clinicians in planning personalised training programs for chronic m-sTBI patients, which is necessary to achieve optimal behavioural outcomes and improved quality of life.