Hi: PET scan is a better way to check for cancer reoccurrence than MRI. MRI can‘t distinguish easily between old scar tissue and active cancer tissue unless there is a difference in size. PET scans can detect “hot” spots that are active.

Hi @donsunlover, This is a difficult decision. Knowing early about a recurrence or progression is so important. I'm very encouraged that we're heading toward a world where we have access to tests such as these as general cancer screenings. The criteria and limitations to our current screening methods are not enough to make most of us feel comfortable.
My understanding is that these tests are detecting tumor cells in the blood stream. My cancer diagnosis was refined to a specific gene mutation by using a blood test from FoundationOne. My tumors were shedding a significant amount of tumor DNA at that time, but as a never-smoker, lung cancer screening never crossed my mind, or my doctor's mind. Testing like this may have identified my cancer at an earlier/curable stage.
One question I would have for this type of testing, is that even if the cloudiness seen on your MRI is cancerous, would that cloud be enough to be shedding cells (or enough cells) to make a determination. Sorry, I know that's not that helpful, more doubt.
Have your MRI results shown any changes over time? How often are you getting scans?