Magnetic Resonance Imaging (MRI): A 3 Tesla MRI will be used to quantify cerebral blood flow and capture cerebral vessel structure at designated time points throughout the study visits (at baseline and during treatment conditions). No contrast agent will be used at any time. The subject will be in the scanner for an initial baseline scan and during the experimental trials. All scanning will be accomplished in the proposed timeline of experimental trials. While in the scanner, subjects will be monitored for heart rate, ECG, end-tidal carbon dioxide (CO2), and blood pressure. The scanner has the capabilities to collect this data, except for end-tidal CO2, which will be collected with a subject monitor. In addition to standard pulse sequences commonly obtained for clinical purposes (localizers, standard MR Angiography for vessel anatomy (without a contrast agent), 2D phase contrast MRI for velocity encoded measurements), a.s.o.; 'basic sequences'), an acquisition scheme developed at the University of Wisconsin-Madison will be used. This scheme, PC VIPR (phase contrast vastly under-sampled isotropic projection reconstruction) is unique in its capability to acquire volumetric data sets with three-directional velocity encoding and high spatial resolution in fairly short scan times. All pulse sequences used in this study are designed to stay within the current guidelines for dB/dt established by the FDA.