I have had many PET scans. Like Brian said about the scan tracking radioactive glucose utilization, while you are healing there is a lot of that in the radiated areas. My doc and I have looked at these images over the years and we almost laugh now. The heart and tongue are nearly pure muscle that even in their calmest state still have very disparate sugar utilization compared to "normal" tissue like a leg muscle for example. Relax as much as possible as often as possible. Take care.