To get the best results of the PET there are several things you need to do. Drink plenty of water the 24 hours prior to the test (60 oz), also avoid all sugar and carbs. You should take it easy and rest the 24 hours before your test too. No exercising at the gym or even taking walks/jogging, you need to relax and rest. This will help your body to project a better picture of whats really going on and help avoid false positives/negatives.

Yes, you could have a false positive for a number of reasons. Both sides of my neck lit up like a Christmas tree, but not one single node tested positive for cancer (they took 45) from either side.

The most common cause is food, but your individual body chemistry can be the cause as well. In my case, as I had been losing weight, my surgeon did not want me to go 24 hours without eating, and my tumor (on my oral tongue) was so painful to touch that I was down to a mostly liquid diet - making it impossible to avoid carbs leading up to the test.