I actually had a couple of MRI's in the past 6 months for the same reason as you: migraines. The second time they did give me a shot to calm me down but that's because I was having a series of migraines that had me hospitalized, and I was in too much pain to just stay motionless for the test. I was scared it was going to make my headache even worse but it wasn't that bad. They gave me hospital headphones to listen to music while it was going on so the noise was loud but not horrible. They found nothing on my MRI. So good luck with yours!
-------------------- Melinda
IBS-A but leans toward C mostly