Jennifer Mathews: You are looking at Alzheimer's disease or more specifically, the traces of brain cells killed by the disease. Dr. Jorge Barrio: And this is not observable in the normal subjects. Jennifer Mathews: Dr. Jorge Barrio, helped pioneer the new technology, he injected patients with a radioactive chemical marker and examined their brains with a PET scan. The images revealed the telltale plaques and tangles that used to be evident only through an autopsy. Co-researcher Gary Small says, catching the disease early is the key to treating it. Gary Small: What we have now is a new technology that for the first time allows physicians to pinpoint the disease in the living patient. Jennifer Mathews: The PET scan may flag patients years before they develop symptoms. Gary Small: We see a lower signal in people without Alzheimer's, but there's a range of signals that we see and we suspect those who have a greater signal, who don't have Alzheimer's, have a higher risk for developing the disease. Jennifer Mathews: Nancy Levitt knows all about Alzheimer's. Her mother has it. Six aunts and uncles had it and her father recently died of the disease. Nancy Levitt: At the end he was more like a shell of a person. I mean, this looks like my father, but what's inside, there is nothing left. Jennifer Mathews: Nancy knows she is at increased risk. Nancy Levitt: I don't want my three children to go through what I went through. Jennifer Mathews: She's considering joining the PET scan study, saying even if it's bad news just knowing may help her prepare. This is Jennifer Mathews reporting.