I signed up as a volunteer for an ALZ trial here locally. With both parents having dementia and/or ALZ, it was important to me. I had interviews, blood and urine tests, mental acuity tests and then a PET scan. I was happy thinking I was helping. But I “failed” the PET test. No amyloid plaques. Good news, but I am booted from the trial. Just sharing.
Congratulations, both on volunteering and on being booted! 
I’d be thrilled to be booted from Alzheimer’s research because a full and thorough evaluation showed that I had no signs of Alzheimer’s. But it was great that you volunteered.
For some reason I was booted from an ALZ trial before I even started. I wanted to participate since my father and two of his sisters had it. I am now the exact age he was when he was diagnosed.
But congrats on your PET scan.