A total 25 healthy subjects will be included in this study. Subjects between 20 and 80 years of age may be eligible for this study. Candidates are screened with a medical history and physical examination, and blood test.

The primary objective of this protocol is to assess the possible age-dependent decline in striatal 18F-DTBZ uptake of healthy subjects.

This study is expected to be completed in a period of 2 years.

Inclusion Criteria:

1. Male or female age 20 years to 80 years.
2. Subjects without significant neuropsychiatric disorder after evaluation by Neurologist.
3. Subjects who provide a written informed consent prior to study entry. If the subject is incapable of informed consent, the caregiver may consent on behalf of the subject (the subject must still confirm assent).

Exclusion Criteria:

1. Pregnancy and breast feeding.
2. Significant recent (within 6 months) history of neurological (including stroke and brain trauma) or psychiatric disorder.
3. Alcohol or substance abuse within last year.
4. Parkinson's disease or other brain degenerative disease (spinocerebellar ataxia, Wilson's disease, hydrocephalus, multiple infarction, history of severe head injury or intracranial operation.
5. Unable to stay still in the MRI or PET scanner for 30 minutes.

one month