I have had a ct scan of my inner ears to look at the bones and it was nothing compared to mri scan. If you having a ct scan then its just like a big doughnut that rotates around you and not scary at all.
If you are having an mri scan then you can ask your consultant to get you an appt in an open scanner that is much better than a closed scanner, you may have to travel out of your area for this though as not many nhs hospitals have open scanners but it is possible to do this on nhs as I have done.
Otherwise your GP can give you some diazepam to take half an hour before the mri scan to calm you, again I have done this as well.