The central goal of this study is to determine and compare the similarities and differences
in regional brain uptake of [18F]T807 in patients with typical Alzheimer's Disease (AD),
Posterior Cortical Atrophy (PCA), and Logopenic Variant of Primary Progressive Aphasia
(lvPPA). The investigators will correlate patterns of [18F]T807 binding with magnetic
resonance imaging (MRI)-based regional volumetric and cortical thickness measures. If
cerebral spinal fluid (CSF) samples are not available, patients may be asked to get an
optional lumbar puncture (LP) for additional comparisons. The investigators will recruit 20
participants, 45-70 years old, with clinical evidence of young onset focal dementia.