This project will collect quantitative pilot data that will allow the characterization of uptake and binding of 18F-AV-1451 (also known as F 18 T807), a novel tau imaging compound, in individuals with Progressive Posterior Cortical Dysfunction (PPCD) and logopenic variant primary progressive aphasia (lvPPA). The primary goal is to develop tau imaging technique as an antecedent biomarker of cognitive decline. The investigators propose to obtain preliminary data that will support the possibility of detecting cognitive decline in its earliest stages, before the occurrence of dementia.

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.

Collaborating physicians and the Knight ADRC Clinical Core will refer participants to the Knight ADRC Research Imaging (KARI) Program for MR and PET imaging to evaluate tau distribution in the brains of cognitively normal and cognitively impaired individuals, with the primary goal of developing this highly promising tau imaging technique as an antecedent biomarker of cognitive decline. We propose to recruit groups of patients with PPCD and lvPPA from the same clinical environment.

We will share this data with other researchers. They may be doing research in areas similar to this research or in other unrelated areas. These researchers may be at Washington University, at other research centers and institutions, or industry sponsors of research. We may also share your research data with large data repositories (a repository is a database of information) for broad sharing with the research community. If the individual research data is placed in one of these repositories only qualified researchers, who have received prior approval from individuals that monitor the use of the data, will be able to look at the information.