 Siemens Molecular Imaging SMI is seeking to determine if F-18T808 might be useful as a non-invasive assessment tool in the clinical evaluation of subjects with conditions associated with tau protein aggregates, such as Alzheimers disease. The information collected under this exploratory study will not be used for diagnostic purposes, assessments of the participants 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-18T808. These data will aid in the design of future studies of F-18T808 in patients with Alzheimers disease. Overall, this study will provide initial data that inform the development of F-18T808 as the first PET imaging agent for human tau protein related pathology. 