An MRI of the brain was performed on a 3T high-field scanner (Magnetom Tim Trio; Siemens Healthcare AG, Erlangen, Germany) with gradient field strength of up to 45 mT/m (72 mT/m effective). For DTI the anatomic data were obtained in a T1-weighted, 3-D magnetization–prepared rapid gradient echo (MPRAGE) sequence (repetition time [TR] = 900 ms, echo time [TE] = 3 ms, field of view (FoV) = 23
× 23 cm, acquisition matrix size = 512
× 256 reconstructed to 512
× 512, reconstructed axial planes with 1.2-mm slice thickness). Diffusion tensor imaging was performed in the axial plane with 4-mm slice thickness by using a single-shot, spin echo, echo planar imaging diffusion tensor sequence, thus covering the whole visual pathway (TR = 3400 ms, TE = 93 ms, FoV = 23
× 23 cm, acquisition matrix size = 256
× 256 reconstructed to 512
× 512, number of signal averages = 7, partial Fourier acquisition = 60%) (
Fig. 1A). Diffusion weighting with a maximal
b-factor of 1000 s/mm
2 was carried out along 15 icosahedral directions complemented by one scan with
b = 0. Data sets were automatically corrected for imaging distortions and coregistered in reference to T1-weighted MPRAGE images. To analyze WML, a T2-weighted 3-D FLAIR sequence was used with sagittal acquisition. One-mm-thick slices were reconstructed (TR = 5000 ms, TE = 388 ms, FoV = 25 × 25 cm, resolution = 512 × 512).
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