• Subjects must understand the nature of the study and must provide signed and dated written HRA-approved informed consent in accordance with local regulations before any protocol-specific screening procedures are performed;

• Males and females, age 25-85 years, inclusive;

• Women of child-bearing potential must use protocol-defined contraceptive measures and must have a negative β-hCG test at screening. For sexually active subjects (except females of non-childbearing potential-e.g., at least 2 years postmenopausal or surgically sterile), condoms should be used in addition to other birth control methods for the duration of the study and for 3 months after the last administration of PET or SPECT ligands. These patients must be willing to remain on their current form of contraception for the duration of the study. All male subjects must agree to refrain from donating sperm for the duration of the study and for 3 months after the last administration of PET or SPECT ligands. Sexually active male subjects must agree to use condoms to protect their partners from becoming pregnant for the duration of the study and for 3 months after the last administration of PET or SPECT ligands (i.e. for 15 consecutive months following baseline PET and SPECT scans); agree to ensure that they and their partners are routinely using a medically approved contraceptive method. It is important that male subjects not impregnate others for the duration of the study and for 3 months after the last administration of PET or SPECT ligands;

• Able and willing to participate in all scheduled evaluations, abide by all study restrictions, and complete all required tests and procedures;

• Adequate visual and auditory acuity to complete the psychological testing;

• In the opinion of the investigator, the subject must be considered likely to comply with the study protocol and to have a high probability of completing the study.