Study was terminated in anticipation of transfer of ownership to Avid Radiopharmaceuticals.

[F-18]T808 is being developed as a diagnostic radiopharmaceutical for PET imaging of the human brain.

Siemens Molecular Imaging (SMI) is seeking to determine if [F-18]T808 might be useful as a non-invasive assessment tool in the clinical evaluation of subjects with conditions associated with tau protein aggregates, such as Alzheimer's disease. The information collected under this exploratory study will not be used for diagnostic purposes, assessments of the participant's response to therapy or for clinical management of the participants. However, this exploratory study will provide baseline information on the safety, biodistribution, and dosimetry of [F-18]T808. These data will aid in the design of future studies of [F-18]T808 in patients with Alzheimer's disease. Overall, this study will provide initial data that inform the development of [F-18]T808 as the first PET imaging agent for human tau protein related pathology.

Low Probability for AD Participants (Group 1)

• Participant is of any race/gender/ethnicity who has reached his or her 55th birthday at the time of informed consent.
• Participant provides written informed consent Participant is capable of complying with study procedures
• Participant is capable of communicating with study personnel
• Participant understands and speaks English
• Participant has at least an 8th Grade education
• In the Investigator"s opinion, participant has a low probability of being currently positive for AD as determined by a Mini Mental State Examination (MMSE ≥ 28) defined in APPENDIX VI of XXX protocol
• Participant has no significant hepatic or renal disease as defined by previous medical history and lab results are within the following ranges: Total bilirubin within 2x institutional upper limits of normal AST (SGOT) ≤ 2.5 x institutional upper limits of normal ALT (SGPT) ≤ 2.5 x institutional upper limits of normal Creatinine ≤ 2x institutional upper limits of normal BUN within 2x institutional upper limits of normal

High Probability for AD Participants (Group 2)

• Participant is of any race/gender/ethnicity who has reached his or her 55th birthday at the time of informed consent.
• Participant or participant"s legally acceptable representative provides written informed consent Participant is capable of complying with study procedures
• Participant is capable of communicating with study personnel
• Participant understands and speaks English
• Participant has at least an 8th Grade education In the Investigator"s opinion, *participant has a high probability of being currently positive for AD that is determined by a Mini Mental State Examination (MMSE < 17) defined in APPENDIX VI of XXX protocol
• Participant has no significant hepatic or renal disease as defined by previous medical history, and lab results are within the following ranges: Total bilirubin within 2x institutional upper limits of normal AST (SGOT) ≤ 2.5 x institutional upper limits of normal ALT (SGPT) ≤ 2.5 x institutional upper limits of normal Creatinine ≤ 2x institutional upper limits of normal BUN within 2x institutional upper limits of normal