No, I don't know how to check credentials. I have wondered how accurate the technicians are who interpret the scans. However, after a couple of years of scans showing similar results, I assume the numbers are reasonably correct. Maybe.

Get a scan somewhere else if you are concerned. Cities can have centers where they are not as expensive to get one. Do your research. Maybe even consult another doctor. I consulted three before making my decision to begin medication and it helped me be more at peace with my decision.

I have scan at Kaiser they have never steered me wrong over the years :