All images were acquired on a 1.5 Tesla (Siemens, Erlangen, Germany) whole body scanner equipped with an eight channel phase array head coil. In all the subjects sagittal T1-weighted images were acquired to locate the prescribed positions of the anterior-posterior commissures (AC-PC). Conventional T1W, T2W images were acquired with MRI slices aligned parallel to the AC-PC line to screen the subjects for other cerebral anatomical abnormalities such as traumatic brain injury and old hemorrhagic infarcts etc. SWI imaging was performed with a 3D spoiled gradient recalled echo sequence with the following parameters: TR/TE: 49/40 ms, flip angle: 20°, slice thickness: 2.1mm, no of slices: 56, FOV: 250×203 mm, matrix size: 260x 320. For the analysis, the images were high-pass filtered by using a low spatial frequency kernel of central matrix size 64×64. The resulting image is the SWI filtered phase image. The filtered phase image served as an indicator of phase variations and hence the concentration of iron. The details of the measurement of iron in the order of μg Fe/g tissue is described elsewhere.9 (link),20 (link),21 (link). The 3-D FLASH volumetric scans were also acquired for the anatomical localization based on surface landmarks.