The aim of this study is to evaluate the efficacy, safety of a single dose of BAY 94-9172 (ZK 6013443) as an investigational medicinal product (IMP) in detecting cerebral protein-plaque (amyloid beta) with positron emission tomography (PET). IMP binds to amyloidal beta protein accumulating in brain tissue already from early stages of Alzheimer's disease (AD). IMP is therefore a potential tracer to be used for detecting amyloid plaques. For each subject it is required to visit the study centre during the screening phase, on the PET imaging day and for 1 follow-up visit on the next day. A telephone call for safety follow-up will be performed 7 days after IMP administration. During the screening phase the subject's medical, neurological and surgical history, specific laboratory tests related to AD, MRI of the brain and certain neuro-psychiatric tests will be performed. Clinical safety measures (physical examinations, vital signs, electrocardiogram (ECG) and laboratory tests) will be performed on the PET imaging day before IMP injection and monitored during and after two PET imaging sessions. Clinical safety measures will be performed again on the follow-up visit next day. The results of PET imaging with IMP will be compared between probable AD patients and healthy volunteers (HV). The clinical diagnosis is based on international validated and accepted criteria and established after comprehensive clinical and neuro-psychiatric examinations