You are right on. First if they do a CT and suspect a shadow that may or may not look remarkable, they then will go to an MRI w/o contrast. Sometimes without contrast is useless, others it will highlight the suspious area right away. Most doc's here in the U.S. do order w/o and do a comparison. If the the MRI comes back very conculsive of an anomilie, they will then do a PET which is the upmost conclusive for cancer tumors. But, if the tumor is benign, it will not radiate and light up red. It will only show as another dark showdow. PET is only used to rule out any kind of cancer cells the are malignient.
I know how hard it must be for you to have to beg and on your knees for a test. But, wait and see and don't stress yourself out about it. Sounds like you have had what needs to be done with perphaps nothing even found. Keep you chin up.
Besides, PET scans are worse the MRI's. They are loader and longer. But, I willl say this much. They are sure advanced technology IMHO. I worked at a hospital that had the privledge of having one of the first closed PET scanners. They are a beautiful piece of medical equipment.
Carrie