PET Imaging Tau Accumulation in FTLD and Atypical Alzheimer's Using [18F]-PI-2620

This study uses a specialized PET scan with a radioactive tracer called [18F]-PI-2620 to image tau protein buildup in the brains of people with frontotemporal dementia (FTD) or atypical Alzheimer's disease, as well as healthy volunteers. Tau tangles are a key feature of many dementias and being able to image them can help with diagnosis and research. **You may be eligible if...** - You are 18 years or older and enrolled in the UNICORN study at the University of Pennsylvania - You are either cognitively healthy (as a comparison participant), or have been diagnosed with frontotemporal dementia, atypical Alzheimer's disease, or a related condition - You are able to complete the required cognitive assessments and brain imaging **You may NOT be eligible if...** - You have significant claustrophobia that prevents lying in a PET scanner - You have metal implants or other contraindications to brain imaging - You are pregnant or breastfeeding - You are unable to provide informed consent Talk to your doctor to see if this trial is right for you.