The diffusion weighted imaging scans were acquired on a 3.0T Siemens Tim Trio MRI scanner. Three diffusion echo-planar imaging sequence with one zero-weighted image (b =0 s/mm2) and thirty diffusion sensitizing orientations (b =1000 s/mm2) was used with the following specifications: slice thickness=2 mm; 90 slices; repetition time = 11000 ms; echo time = 98 ms; voxel size = 2 mm isotropic; flip angle=90°; acquisition matrix = 128 mm×116 mm .