 Both healthy subjects and patients will be excluded if they have more than moderate hypertension. The subject may be on anti-hypertensive medications. The initial screening must show no more than moderate hypertension- i.e. less than 16095. On baseline evaluation on the day of the scan i.e., before injection of tracer, the subject must be asymptomatic no headache, dizziness, neurological symptoms, or blurred vision AND have sustained BP less than 180100. 