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Brain imaging

New imaging technologies have revolutionized our understanding of the structure and function of the living brain.

*Structural imaging provides information about the shape, position or volume of brain tissue. Structural techniques include magnetic resonance imaging (MRI) and computed tomography (CT).

*Functional imaging reveals how well cells in various brain regions are working by showing how actively the cells use sugar or oxygen. Functional techniques include positron emission tomography (PET) and functional MRI (fMRI).

Currently, a standard medical workup for Alzheimer's disease often includes structural imaging with MRI or, less frequently, CT. These images are used primarily to detect tumors, evidence of small or large strokes, damage from severe head trauma or a buildup of fluid.

Promising areas for brain imaging research

Researchers are studying whether the use of MRI and other imaging methods may be expanded to play a more direct role in diagnosing Alzheimer's. Many studies have shown that the brains of people with Alzheimer's shrink significantly as the disease progresses.

Research has also shown that shrinkage in specific brain regions may be an early sign of Alzheimer's. However, scientists have not yet agreed upon standardized values that would establish the significance of a specific amount of shrinkage for any individual person at a single point in time.

Research with PET and other functional imaging methods also suggests that those with Alzheimer's typically have reduced brain cell activity in certain regions. However, as with the shrinkage detected by structural imaging, there is not yet enough information to translate these general patterns of reduced activity into diagnostic information about individuals.

At this time, PET is used primarily in research studies in hopes of gaining further knowledge about its potential for wider use in diagnosing Alzheimer's and monitoring progression and response to treatment.

Today, Medicare will cover a PET scan for Alzheimer's only to help distinguish the disease from frontotemporal dementia, a rare related disorder that may cause dramatic loss of function in the front and side regions of the brain.

Another promising area of functional imaging research focuses on developing tracer compounds that will attach to key abnormal brain deposits implicated in Alzheimer's. For example, preliminary data suggests that one such tracer, called Pittsburgh compound B, may attach to beta-amyloid and light up in a PET scan.