Diffusion basis spectrum imaging detects axonal injury in the optic nerve following traumatic brain injury

Purpose: To utilize diffusion basis spectrum imaging (DBSI), an advanced imaging modality that has been shown to distinguish between co-occurring white matter pathologies, to discern changes in the optic nerves among patients with traumatic brain injury (TBI). Methods: Seven patients with TBI were prospectively recruited to undergo a 3 T magnetic resonance imaging brain scan within two months of injury, and follow-up scans at 6- and 12-months. The optic nerve was considered the region of interest. Manual alignment of the optic nerve slices was performed, followed by the deployment of an in-house script to obtain post-processed data. Diffusion tensor imaging and DBSI-derived axial (AD) and radial diffusivity (RD), reflecting axon and myelin integrity, respectively, were compared. DBSI-derived signal intensities were also compared. The Kruskal-Wallis test was performed to determine significance (p < 0.05). Results: Fourteen optic nerves from patients were compared with 18 optic nerves from control participants. The values of DTI RD were significantly greater among patients than controls (p < 0.05) across all timepoints, with no corresponding differences in the AD. However, a decrease in DBSI AD (p < 0.01) observed only at the initial scan, coupled with a stable RD, was observed among patients. Comparisons between DBSI signal intensities among patients showed no appreciable differences; however, the fiber fraction was significantly lower (p < 0.05) at all timepoints. Conclusion: Acute reductions in DBSI-derived AD and sustained reductions in fiber fraction can serve as a potential biomarker for axonal injury in the optic nerves of patients with TBI.