2.5. Analysis
All participants’ FA data were then processed with the FSL
software package Tract-Based Spatial Statistics (TBSS) (Smith et al.,
2006). The subjects’ FA images were aligned into a common space
using FMRIB’s nonlinear image registration tool (FNIRT) (Andersson
et al., 2010), which uses a b-spline representation of the registration
warp field (Rueckert et al., 1999). Next, the mean FA image was
calculated and thinned to create a mean FA skeleton, which represents
the centers of all tracts common to the group. The threshold
for the mean FA skeleton was set at 0.2, resulting in a mask of
149,473 voxels. Each participant’s aligned FA data were then projected
onto this skeleton. Nonlinear warps and skeleton projection
stages were repeated using MD values.