Fig. 5: Methodology for calculating the DTI-ALPS index.

A Color-coded fractional anisotropy (FA) map indicating fiber orientations: projection fibers (blue, z-axis), association fibers (green, y-axis), and subcortical fibers (red, x-axis). Three 5 × 5 mm² regions of interest (ROIs, white squares) were manually placed to measure diffusivity along each fiber type. B Schematic representation of the perivascular space (PVS) orientation relative to projection and association fibers. DTI diffusion tensor imaging analysis along the perivascular space, FA fractional anisotropy, PVS perivascular space, ROI region of interest.