Multimodal MRI Cerebral Blood Flow Assessment

All scans were acquired on a 1.5-Tesla Signa system (General Electrics (GE), Waukesha, WI). In the first session when subjects were at rest, imaging with pCASL was followed with phase contrast (PC)-MRI for quantification of total CBF (tCBF). Anatomical imaging was acquired for brain tissue segmentation. The pCASL imaging was performed with the product sequence from GE [14 (link)], which adheres almost completely to the recently internationally recommended implementation of ASL [6 (link)]; a 3D fast spin echo (FSE) using spiral acquisition and background suppression with a scan time of 5 minutes (TR ⁄TE = 4678 ⁄ 9.8 msec, labeling duration 1500 msec, post labeling delay 1525 msec, 512 sampling points on eight spirals; reconstructed matrix 128x128, three averages, slice thickness 4 mm, FOV 24 cm). A PC-MRI scan (TR ⁄TE = 20⁄6.2 msec; flip-angle, 9°; FOV, 22 cm; matrix, 256x256; slice thickness 5 mm; velocity encoding 100 cm/sec) for measuring mean tCBF was prescribed on a PC-MRI sagittal localizer image perpendicular to the carotid arteries at the level of the mid basilar artery (Fig 1). The anatomical image protocol has been described in detail elsewhere [15 (link)] and included T1-weighted 3D spoiled gradient echo, proton density/T2-weighted FSE and fluid attenuated inversion recovery (FLAIR) sequences.