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

The overall research questions to be addressed by this protocol are as follows: * To assess the dynamic uptake and washout of (123I) MNI-168, a potential imaging biomarker for β-amyloid burden in brain, using single photon emission computed tomography (SPECT) in Alzheimer's (AD) subjects and similarly aged and gender matched healthy controls. * To perform blood metabolite characterization of (123I) MNI-168 in healthy and AD subjects to determine the metabolic fate and nature of metabolites in assessment of (123I) MNI-168 as a single photon computed tomography (SPECT) brain imaging agent. * To acquire initial safety data following injection of (123I) MNI-168. * Obtain test/retest reproducibility information in AD subjects with (123I) MNI-168 based on initial studies.