The role of neuroimaging in dementia

Current advances in our understanding of the various dementias, and Alzheimer's disease (AD) in particular, have led to a high level of clinical diagnostic accuracy. Although much of our information about diagnostic accuracy is derived from research center experience, clinical accuracy for AD is consistently above 85% and has been reported to achieve levels of accuracy above 90%. Although clinical diagnostic accuracy may be somewhat lower in a community setting and in very early stages of AD, current clinical standards are moving toward an inclusive approach to making the diagnosis of AD. Much of the change in diagnostic focus reflects our ability to treat the disease. Neuroimaging technology is playing a greater role in assisting the clinician with the diagnosis of various dementing disorders. A variety of methods both sensitive and specific to the anatomic or physiologic brain changes now known to accompany various dementing disorders are generally available. These methods include high-resolution brain structural imaging with MR imaging or CT, and functional neuroimaging techniques, such as single photon emission CT (SPECT) and positron emission tomography (PET). In addition to clinical application for the diagnosis of dementia, these techniques also offer the opportunity to examine structural, functional, and biochemical changes in the brain leading to new insights regarding the pathophysiology of the various dementias. This article focuses primarily on AD, but includes comment on other dementias, especially with regard to using neuroimaging as a tool for differential diagnosis. The article begins with a brief review of the pathologic brain changes that accompany AD and the technical aspects of the currently available neuroimaging technologies. The body of the article focuses on the clinical applications of these methods for the diagnosis of various dementing illnesses. Some promising new methods of image analysis and exciting new technologies are introduced at the end of the article.