Improving Specificity in Fixel-Based Analysis

Motivation: Fixel-based analysis in diffusion MRI is widely used but its ability to specifically isolate changes in affected fibres remains underexplored. Goal(s): To assess and improve the specificity of fixel-based metrics in detecting changes in affected fibres without cross-contamination from crossing fibres. Approach: Diffusion MRI data from a mouse model of unilateral retinal ischemia were analysed using basic and extended ball-and-stick models, with the extended model incorporating perpendicular diffusivity as a parameter. Results: The basic model identified injury but lacked specificity. The extended model improved specificity, showing unchanged results in intact fibres and increased perpendicular diffusivity in injured fibres. Impact: This study improves the specificity of fixel-based analysis in diffusion MRI, allowing for more accurate detection of fiber-specific microstructural changes. It paves the way for tract-specific metrics that could enhance the diagnosis of neurological conditions with selective fibre degeneration.