## 2 Materials and Methods
### Structural MRI Acquisition  
Imaging was performed on a 3 Tesla MR system (Siemens Trio Tim System, Siemens Healthcareers, Erlangen, Germany), in a standardized supine position using a 12-Channel Head Coil (Siemens Healthcareers, Erlangen, Germany). Structural MRI included following sequences: 3D FLASH MRI along 3 orthogonal directions to obtain scout views of the brain for initial positioning of MRI slices (voxel size: 1.6 \(\times\) 1.6 \(\times\) 1.6 mm, matrix size = 160 \(\times\) 160, total acquisition time: 17 s); sagittal volumetric T1-weighted gradient echo MRI (MPRAGE) of the entire brain, TR/TE/TI = 1900/2.52/900 ms, 9\({}^{\circ}\) flip angle sequence with a spatially isotropic resolution of 1.0 mm\({}^{3}\) (matrix size = 256 \(\times\) 256, total acquisition time: 4:26 min); sagittal single slab 3D turbo spin echo sequence with slab selective, variable excitation pulse to obtain proton density and T2-weighted MRIs, TR/TE/TI = 5000/388/1800 ms, 176 contiguous slices (1 mm) covering the entire brain with a spatially isotropic resolution of 1.0 mm\({}^{3}\) (matrix size = 256 \(\times\) 259, total acquisition time 6:27 min); axial diffusion weighted imaging (DWI) with TR/TE = 3800/91 ms, a slice thickness of 5 mm, FOV = 230 mm (voxel size: 1.2 \(\times\) 1.2 \(\times\) 5.0 mm, matrix size = 192 \(\times\) 192, total acquisition time 1:21 min); axial 3D fast low-angle gradient-echo sequence (SWIMR), TR/TE = 28/20 ms, FOV = 230 mm, slice thickness of 2 mm with a spatially anisotropic resolution of \(0.7\times 0.6\times 2.0\) mm (matrix size = 384 \(\times\) 353, total acquisition time 5:26 min). To rule out intra- and extra-cranial stenosis, which could compromise arterial spin labeling technique we performed intra- and extracranial angiography and contrast-enhanced brain perfusion. Angiography MRI included: 3D time-of-flight MRA spoiled gradient echo (TOF) of the circulus arterious cerebri with TR/TE = 22/3.98 ms, 15\({}^{\circ}\) flip angle sequence with FOV = 220 mm, slice thickness/slice oversampling = 0.7 mm/25%, and bandwidth = 181 Hz/Px (voxel size: 0.7 \(\times\) 0.4 \(\times\) 0.7 mm, matrix size = 512 \(\times\) 307, total acquisition time 5:37 min); contrast-enhanced MRA with a weight-adapted dose of Gadobutrol (Gadovist\({}^{\circ}\), Bayer Healthcare, Leverkusen, Germany), 0.1 mL/kg) injected at a rate of 3 mL/s, TR/TE 43.46/1.56 ms, 25\({}^{\circ}\) flip angle, bandwidth 400 Hz/Px, 90 measurements (voxel size: 0.7 \(\times\) 0.4 \(\times\) 0.7 mm, matrix size = 256 \(\times\) 179, total acquisition time 1:30 min); dynamic susceptibility contrast (DSC) MR perfusion with a second weight-adapted dose of Gadobutrol (0.1 mL/kg) injected at a rate of 5 mL/s, a T2* echo planar imaging (EPI) gradient recalled-echo sequence was used, TR/TE = 1840/32 ms, 90\({}^{\circ}\) flip angle, bandwidth 1346 Hz/Px, slice thickness = 6 mm, 19 sections (matrix size = 128 \(\times\) 128, total acquisition time 1:39 min); postcontrast structural MRI included the following sequences: postcontrast axial T1 fast low-angle shot (FLASH) sequence with TR/TE = 309/4.92 ms, 90\({}^{\circ}\) flip angle (voxel size \(0.5\times 0.5\times 5.0\) mm, matrix size = 448 \(\times\) 448, total acquisition time 2:41 min); postcontrast axial T1 volumetric interpolated brain examination (VIBE) 7 sequence with TR/TE = 3.93/1.5 ms, 9\({}^{\circ}\) flip angle (voxel size = 0.9 \(\times\) 0.9 \(\times\) 2.0 mm, matrix size = 320 \(\times\) 320, total acquisition time 2:44 min).