For the diffusion MRI data, the diffusion tensor was computed using the Diffusion Toolbox (FDT) from the FMRIB software library, (61–63; FSL, v.4.0.1, http://www.fmrib.ox.ac.uk). Each diffusion weighted volume was aligned to the b0 image using an affine transformation to correct for the distortions caused by eddy currents (64). The entire diffusion series was corrected for geometric distortion caused by magnetic field inhomogeneity using FMRIB’s Utility for Geometrically Unwarping EPIs (FUGUE) in conjunction with the b0 field maps. The diffusion tensor was derived from the b0 image and the twelve aligned, distortion corrected diffusion weighted images. Fractional anisotropy (FA) and mean diffusivity (MD) images were created from the diffusion tensor eigenvalues. FSL’s tract-based spatial statistics (TBSS) program was used to align the FA and MD images so that voxelwise statistical analysis could be performed between time points and across participants.
