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Illuminating Alzheimer’s: Physicians can detect signs of Alzheimer’s in the living human brain thanks to a new imaging tool. High levels of amyloid plaques, a hallmark of the disease, are marked in red. Credit: Avid Radiopharmaceuticals.

An advisory panel for the U.S. Food and Drug Administration gave conditional approval on Thursday for a new imaging agent that could aid in early detection of Alzheimer’s. if the FDA follows the panel’s recommendation, as it usually does, it will be the first such tool available to physicians to detect amyloid plaques, the neurological hallmark of the disease, in the living human brain.

As I noted in a story we posted yesterday on the technology, experts say the tracer will be especially useful in future research studies testing drugs designed to prevent the brain damage that causes Alzheimer’s, as well as in diagnosing difficult and atypical cases of the disease.

The tracer, developed by Avid Radiopharmaceuticals (recently acquired by Eli Lilly) binds to amyloid plaques in the brain and is detected via position emission tomography (PET) scans. Previously, the only definitive way to detect amyloid in the brain, and hence definitely diagnose the disease, was via an autopsy.

The approval is conditional on the development of standards that make reading the scans consistent between radiologists and a doctor-training program. According to a report from the New York Times,

The question about interpreting the scans arose because in the Avid study, radiologists did not establish a firm cutoff point that would say whether a person had significant amounts of plaque. Instead they did a graded analysis. What is needed in practice is a set level that would say yes or no, and distinguish significant plaque accumulation from insignificant amounts. and the company must show that its cutoff points are accurate and that different radiologists assess the same scan in the same way.

Some people have plaque without having Alzheimer’s, so if a scan shows plaque, doctors will have to use their clinical judgment, taking into account a patient’s symptoms, in deciding what the scan results mean, noted Dr. P. Murali Doraiswamy, an Alzheimer’s researcher at Duke University and a clinical investigator in the Avid trial. but if a scan shows no plaque, the situation is simpler, Dr. Doraiswamy said. It means the doctor should focus on other causes for the symptoms.