All subjects will return for their close-out visits 33-35 days after enrolling in the study and will undergo brain ASL and perfusion MRI and have blood drawn for biomarkers at that visit. The study will be conducted at 4 sites (MUSC, MCG, UCLA, USC) to enable us to evaluate the consistency of CBF measurements across multiple sites and to ensure that the recruitment target of 10 subjects will be met in time to allow for the subsequent NIH grant submission in 2017.