Imaging of Alzheimer's disease.

Imaging is widely used in the evaluation of Alzheimer's disease (AD). In addition to imaging's traditional role of aiding in the exclusion of diseases that may be confused with AD, structural and functional imaging are being explored for potential use in the early detection of AD and as surrogate markers of treatment outcome. Volumetric measurements of the hippocampal and entorhinal regions using modern magnetic resonance imaging (MRI) and computed tomography are most widely studied in the discrimination of AD from nondemented aging and other dementias. Other imaging modalities include positron emission tomography and single-photon-emission computed tomography, which evaluate global and regional disturbances of blood flow and metabolism, and proton spectroscopy, which assesses neuronal degeneration and loss as marked by the presence of abnormal metabolites. Diffusion tensor and functional MRI, which examine white matter changes and brain-behavior relationships, are more recent techniques that contribute to the burgeoning application of imaging techniques to dementing illnesses and are notably improving our understanding of the pathophysiology of AD.