The second decade of DTI in TBI part 1: a systematic review of mild TBI.

Background: Traumatic brain injury (TBI) is a pervasive and important public health concern. TBI can range from mild, resulting in headache, dizziness, and imbalance, to severe resulting in coma and death. Diffusion tensor imaging (DTI) offers the ability to assess tissue microstructure at a level inaccessible to classical neuroimaging methods, such as CT and structural MRI. This systematic review aims to explore studies using DTI in mild TBI (mTBI) during the 2012-2022 decade, which is the second decade of reported use. The use of DTI in moderate-severe TBI (msTBI) during this time period is discussed in our companion systematic review. Methods: A systematic literature review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched the electronic databases PubMed/MEDLINE, Embase, Cochrane Library, and Web of Science from 2012 through September 28, 2022. Results: A total of 325 studies on mild TBI were included, which encompassed 26,287 participants. There were more longitudinal studies in 2012-2022 compared to the prior decade (29.85 vs. 13%). Fractional anisotropy (FA) and mean diffusivity (MD) were the most commonly used DTI measures. Regardless of acquisition techniques and analysis methods, the majority of studies that compared FA between those with mTBI and controls, found lower FA in mTBI patients compared to controls, but less consistently than in msTBI. Lower FA was associated with worse cognitive outcomes across domains, but associations with clinical post-concussive symptoms were more mixed. Conclusion: Since its first decade (2002-2012) of reported use, DTI applications to mTBI have continued to expand in both quantity and scope, including notable increases in the proportions of larger and longitudinal studies, those employing whole brain analyses and those addressing clinical and cognitive outcomes. The most salient feature of the study results remains that low FA is the most common finding identified in mTBI patients compared to controls, however the direction of the FA effect is more variable for mTBI compared to msTBI. Systematic Review Registration: Prospero [CRD42022361318], https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=361318.