Functional and structural brain imagings in dementia.

Dementia is a major psychiatric problem in elderly people. Recent developments in brain imaging have made practical contributions to the diagnosis of dementia, which is caused by spread of various kinds of lesions in the brain. It is important to make accurate diagnoses of dementia in living patients, in order to decide upon treatment and to predict life expectancy. Magnetic resonance imaging can reveal vascular lesions more sensitively than can X-ray computed tomography. Imaging methods of brain structures, however, can show only atrophies in dementing disorders caused by degeneration, like Alzheimer's disease. In contrast, functional imaging methods like single-photon emission tomography and positron emission tomography, measuring regional cerebral blood flow and/or metabolism, have capabilities to detect hypofunctional brain areas, before structural changes appear in the degenerative dementias. A specific finding for Alzheimer's disease in emission tomographic examinations is relative hypofunction of the posterior cerebral association cortices on both or one side in dementia without evidence of any cause for the dementia. This finding is expected to be positive evidence for the diagnosis of Alzheimer's disease.