F 18 T807 Tau PET Imaging of Progressive Posterior Cortical Dysfunction (IND 123119, Protocol E)

Inclusion Criteria: 1. Male or female participants, at least 45 years of age. 2. Clinical diagnosis of PPCD. 3. Participant is able and willing to undergo testing (MRI or CT, PET, radioactive tracer injection, LP; for those unable to undergo an MRI, CT will be used to generate regions-of-interest). 4. Pre-menopausal women will have a negative urine pregnancy test within 24 hours of T807 drug administration. Exclusion Criteria: 1. Has any condition that, in the Investigator's opinion, could increase risk to the participant, limit the participant's ability to tolerate the experimental procedures, or interfere with the collection/analysis of the data (for example, participants with severe chronic back pain might not be able to lie still during the scanning procedures). 2. Is deemed likely unable to perform the imaging procedures for any reason. 3. Has a high risk for Torsades de Pointes or is taking medications known to prolong QT interval. 4. Has hypersensitivity to F 18 T807 or any of its excipients. 5. Contraindications to PET, PET-CT or MR (e.g. electronic medical devices, inability to lie still for long periods) that make it unsafe for the individual to participate. 6. Severe claustrophobia. 7. Currently pregnant or breast-feeding. 8. For those electing to undergo the optional lumbar puncture: on anticoagulant of any form prior to lumbar puncture.