Brain Imaging Study in Subjects With Alzheimer Disease in Comparison to Healthy Subjects

Inclusion Criteria: * Subjects who have a clinical diagnosis of AD will be recruited for this study * The participant is 50 years or older * Written informed consent is obtained * Participants have a clinical diagnosis of probable Alzheimer's disease based on National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS/ADRDA) criteria * Subjects will have a clinical dementia rating (CDR) assessment score of ≥ 0.5 and \< 2.0 * Modified Hachinski Ischemia Scale score of ≤ 4 * For females, non-child bearing potential or negative urine and blood pregnancy test on day of 123-I MNI-168 injection Exclusion Criteria: * The subject has signs or symptoms of another neurodegenerative disease including Parkinson's disease, diffuse Lewy body dementia, or history of significant cerebrovascular disease * The subject has clinically significant abnormal laboratory value and/or clinically significant unstable medical or psychiatric illness * The subject has any disorder that may interfere with drug absorption distribution, metabolism, or excretion (including gastrointestinal surgery) * The subject has evidence of clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematological, neoplastic, endocrine, neurological, immunodeficiency, pulmonary, or other disorder or disease * The subject has participated in another clinical study within the previous 30 days * Clinically significant MRI evidence of vascular disease or alternative neurologic disorder * Pregnancy