Hi there... a scan of any kind doesn't show up microscopic cancer it has to be a certain size to be picked up. All scans show up inflammation, infection, and healing areas, as well as cancer. It takes a trained professional to figure out what is what on a scan, but even the best can't know for sure without a biopsy to confirm. As far as I know an MRI is more comprehensive that a CT. and a PET is as well. But PET's do have a history of false positives because they pick up high sugar counts in your body. Now cancer is a sugar hog but there tends to be a high amount of carb activity when there is healing or inflammation, etc... taking place. Where I live some drs. still don't trust PETs they generally go for the CT or MRI, but I know in the states they are widely used and popular.

I'm sure someone else will be along to offer more info.

best of luck.