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— By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Dramatic new scans show brain cells quickly and steadily disappearing in patients with Alzheimer's disease, an international team of researchers reported on Thursday.

They used magnetic resonance imaging, also known as MRI, to chart a 5 percent annual loss of brain cells in Alzheimer's patients -- up to 10 percent in key memory areas.

In contrast, healthy volunteers monitored in the study lost less than 1 percent of their brain cells a year.

"For the first time, you can see Alzheimer's disease progressing in living patients," said Paul Thompson, an assistant professor of neurology at the University of California Los Angeles school of medicine, who led the study.

"We were stunned to see a spreading wave of tissue loss. Initially confined to memory areas, this loss moved across the brain like a lava flow, destroying more and more tissue as the disease progressed."

Writing in the Journal of Neuroscience, the researchers said their findings would help doctors check to see if treatments are helping, and perhaps help chart the course of the disease.

Alzheimer's is assessed using standard tests of a patient's behavior and performance, rather than any physical evidence.

This will probably continue to be the case, said Dr. Sid Gilman, director of the Alzheimer's center at the University of Michigan.

"The diagnosis of Alzheimer's disease really depends upon demonstration of cognitive dysfunction," Gilman said in a telephone interview.

"No amount of PET scanning or MRI scanning will make the diagnosis. There are anecdotal stories of people dying who had scored normal on tests of cognitive function a few weeks before and upon death the brain can show definitive signs of Alzheimer's."

CHARTING FUTURE TREATMENT

However, such a test would be extremely useful in charting future treatments, Gilman said.

"Currently all we have is symptomatic treatment," he said. "We have no treatment that stops the progression."

But, he added, researchers are working on ways to stop the now-incurable disease, such as vaccinations that might stop the buildup of toxic proteins in the brain.

"We are on the verge of some very exciting discoveries in Alzheimer's disease, so that a biomarker that told us the disease itself was not progressing would be extremely important," Gilman said.

For their study, Thompson and colleagues at UCLA, in Britain and in Australia scanned the brains of 12 Alzheimer's patients and 14 healthy volunteers. MRI gives a finer image of bodily structures than x-rays.

"They got a scan every three months," Thompson said in a telephone interview.

They were able to put together time-lapse images, which can be seen on the Internet at http://www.loni.ucla.edu/~thompson/AD_4D/dynamic.html.

On average, the Alzheimer's patients lost 5.3 percent of their brain cells each year. In memory regions they lost up to 10 percent.

"Memory systems go first and then the frontal areas involved in inhibition and self-control and later areas involved in emotion," Thompson said.

"Another feature is that some parts of the brain are completely spared. One example is the visual area. Why it is, is a mystery."

Thompson hopes the method could not only be used to compare treatments for Alzheimer's, but perhaps to see if exercise and mental exercise could prevent or delay Alzheimer's in people at a high risk of the disease.

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