Do not let comments like this scare you. I had 5 biopsies before my surgery and none of them were hellish. In fact, they were quite painless for me. I had made myself so anxious the day of my first one for nothing. If you are nervous, ask for a Klonipin or valium (I did this for open MRI and even that was not bad. The noise can be a bit unnerving). We all have different experiences.
And your other question was can an MRI make a cancer diagnosis. No, only a biopsy.