GINA KOLATA

Dr. Daniel Skovronsky sat at a small table in his corner office, laptop open, waiting for an e-mail message. His right leg jiggled nervously.

A few minutes later, the message arrived ? study results that showed that his tiny start-up company, Avid Radiopharmaceuticals, might have overcome one of the biggest obstacles in diagnosing Alzheimer’s disease. It had found a dye and a brain scan that, he said, shows plaque in the brains of people with the disease.

The findings, which were presented at a meeting of the Alzheimer’s Association in Honolulu on July 11, must still be confirmed and approved by the United States Food and Drug Administration. If they hold up, it will mean that for the first time doctors will have a way to diagnose the presence of Alzheimer’s in patients .

And researchers would be able to figure out whether drugs are slowing or halting the disease, a step that “will change everyone’s thinking about Alzheimer’s in a dramatic way,” said Dr. Michael Weiner of the University of California, San Francisco .

Ever since Alzheimer’s disease was described by a German doctor, Alois Alzheimer, in 1906, there was only one way to know for sure that a person had it. A pathologist, examining the brain after death, would see microscopic black freckles, plaque, sticking to brain slices . Without plaque, a person with memory loss did not have the disease.

There is no treatment yet to stop or slow the progress of Alzheimer’s. But every major drug company has new experimental drugs it hopes will work, particularly if they are started early. But who should be getting the drugs and who really has Alzheimer’s or is developing it?

Brain scans that show plaque can help answer those questions and also show whether the disease ever stops or slows down on its own and even whether plaque is the main culprit causing brain cell death.

Dr. Skovronsky thought he had a way to make scans work. He and his team had developed a dye that could get into the brain and stick to plaque. They labeled the dye with a commonly used radioactive tracer and used a PET scanner to directly see plaque in a living person’s brain. But the technology and the dye itself were so new they had to be rigorously tested.

And that is what brought Dr. Skovronsky to his e-mail that recent day. Five years ago, he had taken a big gamble. He left academia and formed Avid Radiopharmaceuticals, based in Philadelphia, to develop his radioactive dye and designed a study with hospice patients to prove it worked.

Hospice patients were going to die soon and so, he reasoned, why not ask them to have scans and then brain autopsies afterward . Some patients would be demented, others not.

Some predicted his study would be impossible, if not unethical. But the F.D.A. said it wanted proof that the plaque on PET scans was the same as plaque in a brain autopsy.

The results of the Avid study, contained in the e-mail message sent that day, May 14, were the moment of truth. When he saw them, Dr. Skovronsky said they were everything he had hoped for.

Experts who attended the Honolulu conference said the data persuaded them that the method works.

Dr. Reisa A. Sperling, an Alzheimer’s expert at Brigham and Women’s Hospital in Boston and a chairwoman of the session where the results were presented, said, “Personally, I found the data quite convincing.”

Dr. Sperling said the challenge now will be to see whether the scans can accurately predict whether people are developing Alzheimer’s before they have symptoms. That is the stage, she said, “where we have the best chance of changing the course of the illness.”

The Honolulu conference decided to support a major change in the diagnostic guidelines for Alzheimer’s disease, advocating that new technology like the Avid brain scans be used to detect the disease even before there are evident memory problems or other symptoms.

The day of the e-mail, Dr. Skovronsky went into Avid’s lunchroom to tell the company’s 50 employees. “This is a big day for us,” he said. “This is going to have a big impact on Alzheimer’s disease, guys.”

His employees applauded. Then they had champagne in blue plastic cups