Information about Radiology and Diagnosing Alzheimer's

CT and MRI scans are used to examine brain structure and function and to rule out other possible causes of mental impairment. A CT scan uses an x-ray method that makes hundreds of images while rotating 360 degrees around the area that is being studied. A computer processes these images to produce two-dimensional cross-sectional images of the area—like slices from a loaf of bread. This technique can rule out some causes of dementia, such as stroke, brain tumor, brain abscess, or hydrocephalus (fluid in the brain). It can also identify enlargement of certain portions of the brain, which may suggest the presence of Alzheimer's disease.

MRI scan can also detect some of the structural changes associated with Alzheimer's disease. Like CT, MRI forms two-dimensional, cross-sectional images of the brain. But MRI relies on a powerful magnet rather than x-rays to capture the images. Because the technique is based on the amount of water in a given tissue, MRI provides a more refined and clearer view of the brain.

A promising development in imaging is a technique called functional MRI that looks not only at the structure of the brain but also at the metabolic processes taking place at the time of the scan. For example, functional MRI can detect changes in brain activity that occur as different areas of the brain are stimulated by tests of, say, memory or mathematical skills.

PET and SPECT imaging examine how the brain is working metabolically by determining how much of a radioactive tracer is taken up by brain cells. A new imaging agent called Pittsburgh Compound B (PIB) now allows researchers to see the earliest deposits of amyloid plaque. Another experimental imaging compound known as FDDNP reveals the presence of neurofibrillary tangles.

PIB and FDDNP are used with PET scans. Functional MRI and PET with PIB or FDDNP may become approved tools for early diagnosis of Alzheimer's; however, their benefit is not yet proven and they are not routinely recommended.

One concern is whether they will be able to identify who will develop dementia before memory decline actually occurs. This would be desirable if earlier treatment were shown to be beneficial. However, there is no evidence that this is currently the case.

Publication Review By: Peter V. Rabins, M.D., M.P.H.

Published: 09 Mar 2011

Last Modified: 28 Aug 2015