SNUH-NM-333 ligand effect was judged to be insufficient.

To evaluate pharmacokinetics, safety and efficacy of SNUBH-NM-333(18F), a new diagnostic radiopharmaceutical for PET imaging of amyloid plaques, in Alzheimer's disease patients and healthy volunteers.

The investigators will perform whole-body and brain kinetic modeling of SNUBH-NM-333(18F) and optimize the image acquisition procedure.

Five young healthy subjects will be participated in Whole-body positron emission tomography /computed tomographic (PET/CT) scans from the midfemoral position to the head after approximately 5-10 mCi of SNUBH-NM-333(18F) injection. For brain PET/CT amyloid imaging, another five young healthy subjects will be scanned dynamically during windows of 0-180 min after injection of SNUBH-NM-333(18F), with arterial sampling.

The investigators will compare different analysis methods of compartmental modeling and standardized uptake value ratios and determine the optimal acquisition window. And then 10 AD patients and 10 elderly healthy controls will also be participated in brain amyloid imaging to compare SNUBH-NM-333(18F) brain retention in AD patients versus healthy elderly.

Inclusion Criteria:

• Healthy young controls who are 20 - 30 years old and have no subjective memrory complaints
• Cognitively normal elderly who have Clinical Dementia Rating score of 0
• Alzheimer's disease (AD) patients who met both the DSM-IV criteria for dementia and NINCDS-ADRDA criteria for probable AD

Exclusion Criteria:

• any present serious medical, psychiatric, or neurological disorder that could affect mental function; evidence of focal brain lesions on MRI; the presence of severe behavioral or communication problems