Neuroimaging in dementia

Dementia is the global and acquired impairment of mental function and is a major health problem, particularly in the elderly. Its most common forms with substantial imaging data are dementia of the Alzheimer's type (AD), frontotemporal dementia, vascular dementia, and Lewy body dementia. The most commonly used imaging modalities are magnetic resonance imaging and emission tomography in their various forms. Imaging can be used for diagnostic purposes. Single-photon emission tomography patterns of temporal-parietal lobe hypoperfusion, for example, differentiate AD from non-AD dementia, with sensitivity between 63% and 86% and specificity between 73% and 93%. Similar data for positron emission tomography are sensitivity of 94% and specificity of 73%. There seem to be typical patterns of brain appearance in each type of dementia, which change over the natural course of the disease, thus giving systematic and potentially complete information that is only available on an accidental basis for pathological data. Neuropsychological function is specifically correlated with particularly functional imaging data, such as brain perfusion and metabolism measures. Combining functional imaging with neuropsychological techniques can help researchers and clinicians to identify regions associated with particular cognitive functions essential for performing a given cognitive task. Imaging of brain receptors has been importantly used to explore the distribution of amyloid, cholinergic, and dopaminergic receptors in patients, thus contributing to the in vivo pharmacology and potentially to the treatment of the dementias.