2050, 52 million will have Alzheimer's disease (AD) worldwide. There are 5.8 million people with Alzheimer's disease in America. It is a common form of dimentia. It is characterized by loss of memory, language and thinking ability. Women are more likely to have AD. Hormonal differences are thought to increase the risk of AD. The biggest risk factor is age. Amyloid plaques can be evaluated by positron emission tomography (PET).