I had a similar situation on an MRI last year. It was very painful to lay on my back in the position the tech put me. Pain was in my left quad, like I've never felt. The bolster didn't help.
He stopped it once because I moved and again for the same reason. I could not withstand the pain. He wrote in my chart I was "uncooperative!" Obviously he doesn't understand pain. It was UPMC Natrona Heights. A few days later my MRI was done at the St Margaret's location. They used a different bolster and it went great; pain free.