Determining the Impact of Shunting and CerebroVascular Reactivity on 7T MRI (DISCoVeR 7T MRI)

Inclusion Criteria: 1. Males and females ≥ 60 years of age. 2. Fluent in English. 3. Part of the NACC longitudinal cohort (Protocol #: 068200) of the PMC/ADCC with consensus conference designation of cognitively normal, Mild Cognitive Impairment, or probable/possible Alzheimer's disease. 4. Has consented to participate in the ADCC high-resolution MRI sub-study. 5. NACC longitudinal visit must be within 6 months of the TCD study and brain MRI study. 6. Women: post-menopausal or surgically sterile. 7. Willing and able to complete all required study procedures. 8. Completed 6 grades of education. 9. Geriatric Depression scale less than 6 (assessed within 6 months at the NACC longitudinal visit). Exclusion Criteria: 1. Prior clinically symptomatic ischemic or hemorrhagic stroke. 2. Inability to tolerate or contraindication to TCD study in the opinion of an investigator or treating physician. 3. Any medical or psychological conditions that, in the opinion of the investigator, would compromise the subject's safety or successful participation in the study.