Alzheimers is a chronic neurodegenerative disease in which the death of brain cells causes memory loss and cognitive decline. A neurodegenerative type of dementia, the disease starts mild and gets progressively worse. The cause of Alzheimers disease is not properly understood. About 70 percent of the risk is believed to be genetic with many genes usually involved. Other risk factors include a history of head injuries, depression, hypertension, age and lifestyle. The disease process is associated with plaques and tangles in the brain. Alzheimers disease is usually diagnosed based on the persons medical history, history from relatives, and behavioral observations. Advanced medical imaging with computed tomography (CT) or magnetic resonance imaging (MRI), and with single-photon emission computed tomography (SPECT) or positron emission tomography (PET) can be used to help exclude other cerebral pathology or sub types of dementia.