The purpose of this study is to determine the value of Arterial Spin Labeling (ASL) MRI, a measure of blood flow to the brain, in Mild Cognitive Impairment (MCI) and compare it to existing measures. In particular, the investigators will compare ASL MRI to Positron Emission Tomography (PET/CT), which measures brain metabolism reflecting how well cells in a patient's brain are functioning. In addition, the investigators will assess the relationship of these measures to specific protein levels associated with Alzheimer's Disease in the patient's cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) obtained by lumbar puncture. By comparing the information that is available from these procedures to the patient's performance on cognitive tests, the investigators hope to learn which procedures most accurately reflect and assist in determination of the potential causes of cognitive difficulties that arise with MCI, and thus, which are most useful in the clinical setting. In particular, PET scans have been found to be very useful in diagnosis of MCI and Alzheimer's Disease, but the investigators want to find out if they can get the same, or better, information from an ASL MRI scan, which is less expensive and easier to acquire.

Inclusion Criteria:

• Males and females between the ages of 55 and 89.
• Fluent in English
• Part of the longitudinal cohort of the PMC/ADCC (must already be or agree to become a part of the Penn Memory Center cohort so baseline neuropsychological testing is available before study participation begins)
• Adequate visual and auditory acuity to allow for neuropsychological testing
• Women: post-menopausal or surgically sterile
• Willing and able to complete all required study procedures
• Completed 6 grades of education
• Geriatric Depression scale less than 6 (assessed within 3 months)

PATIENTS ONLY:

• Diagnosis of MCI
• MMSE between 24 and 30
• Has a study partner

Exclusion Criteria:

• Any contraindication to MRI (i.e. presence of pacemaker, ferrous metal in the eye, severe claustrophobia that would preclude subject from completing the MRI, etc.).
• Major depression, bipolar disorder, history of schizophrenia
• History of substance abuse or dependence within the past 2 years.
• Any medical or neurological condition that, in the opinion of the investigator, would compromise the subject's safety, successful participation in, or integrity of the study.
• Pregnancy
• Recent history of poorly controlled diabetes (e.g. multiple blood glucose reports of ≥ 180 mg/dl.)
• Currently receiving medical or drug treatment contraindicating protocol participation e.g. anticoagulants such as Coumadin/Warfarin

This project will focus on a population enriched in individuals with incipient AD (i.e. MCI). These subjects, as well as age-matched controls, will be recruited from the Alzheimer's Disease Center at the University of Pennsylania.