All DTI scans were performed on a General Electric 3.0-T magnetic resonance imager at the University of California, San Diego. Data with whole brain coverage were collected through a single-shot dual spin echo excitation with TE = 93.4 ms, TR = 12,400 ms, field of view = 24 cm, slice thickness = 3.0 mm, image matrix = 128 × 128, and b-value = 2000 s/mm2. Diffusion-weighted images were acquired in 15 diffusion directions, in addition to the normalization image with no diffusion encoding (b=0) [32]. Four volumes were acquired and averaged for each direction. Each two-dimensional slice was Fourier transformed and re-gridded to rectilinear space prior to the following processing steps.
