PET scans for detecting Alzheimer's disease appear accurate

PET scans to diagnose Alzheimer's disease will be available someday soon, according to accumulating research showing the scans can accurately diagnose the disease.

In two studies published Monday, researchers demonstrated advances in shaping the scanning tools for routine use someday.

In one study, researchers from Banner Alzheimer's Institute in Phoenix evaluated a PET tracer called florbetapir F 18. Tracers are radioactive substances that highlight particular areas of the brain affected by a disease. Researchers found differences in the brain uptake of the tracer between three groups of people: 82 healthy people, 68 people with probable Alzheimer's and 60 people with mild cognitive impairment (considered a precursor to Alzheimer's disease). The scans showed differences large enough to distinguish between impaired and healthy brains. The authors proposed specific cutoff points that could be used to determine a positive test for brain plaques or a negative result.

In a second study, researchers at Penn Memory Center in Philadelphia used a tracer known as fluorine 18-labeled flutemetamol on seven people who had undergone brain biopsies for a condition called normal pressure hydrocephalus. This is a disorder that causes dementia and can be difficult to distinguish from Alzheimer's disease. The study showed the readings regarding plaques seen on the scans matched the visual evaluation of the biopsied tissue.

The cutoff points that are ultimately used to determine a positive or negative result for an Alzheimer's PET scan will be difficult to establish, suggests the author of a commentary accompanying the studies, because different tracers may require their own set of cutoff points. Moreover, the interpretation of the person examining the scan may also be an issue.

The papers appear in the Archives of Neurology.

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