A PET scan detects elevated metabolic activity in tissues. If the scan shows a "hot spot" in an area where there wouldn't normally be increased activity, it's considered a likely cancer. The problem is, garden-variety tissue inflammation also reflects elevated metabolic activity. So if your mouth is still sore, and if that's accompanied by any tissue inflammation, then you could get a "hot spot" on your PET scan that looks just like cancer -- a false positive. That's the risk of having a PET scan done too early in your recovery process. My oncologists are waiting months before scanning me. I finished radiation on June 4, and they are tentatively planning on September -- at least 3 months later -- just to make sure all the tissue inflammation subsides first. I'm sure that if I still have mouth soreness at end of summer, they'll delay scanning even longer. If you still have mouth soreness and your scan time is approaching, you may want to raise this issue with your doctors. You don't need the stress (and wasted cost) of a false positive.