My understanding is that the answer to your specific question is YES, MRI's have lower false positives on BOT oral cancer after TX then Petscans.
But don't worry, if the Petscan does light up, the doctors will just do an MRI to see what is really happening.
I seem to recall that the NCC guidelines for BOT cancer indicate MRIs as the standard but I've gotten their technical issues wrong before.
Still, If I were you, I would have Kevin just follow his doctor's advice and get the Petscan. It's not "wrong" just a difference of opinion and I'm not a doctor. He/She has probably had accurate results from petscans, while I did not.
Plus, getting a totally clean Petscan, that no high SUV report, would be really really comforting to you both
Keep the Faith
Charm