Daniel, the hospital I deal with uses a combination PET/CT, does both scans at the same time, and the end result is a kind of rotatable 3D image on the computer screen, or printed image on paper.
I think the idea is that they compliment each other, the CT shows the mass, and the PET highlights weather it's cancerous or not.
Problem is, the PET works on glucose uptake, so maybe a sore muscle that's healing could show up as positive, as well as infectous lymph nodes. I dont' think any imaging product can tell for sure if there is cancer, just that there is something unusual going on. The only "for sure" is biopsy, either fine needle or other.
The one other advantage of the PET/CT approach is that if the hospital has the whole system, including the IMRT radiation accelerator, then it all links together by computer for more accurate radiaton treatment.
I'm just coming from the "user" standpoint, others have more supplier side information so might be more helpful.
Bob S.