I got very twitchy when going for an MRI scan - I don't do enclosed spaces very well, and the helmet thing on as well - yuk, shudder etc.
I found I calmed myself down by mentally singing Genesis and Yes songs. A quick rendition of "Squonk" followed by a run though of "Awaken" managed to keep me calm - had to speed up Suppers Ready to get it completed before the end of the scanning process though

Would prefer to sing something a little more country - some Emmylou or Patty Griffin perhaps, but I only listened to prog rock in the days when I read lyric sheets so they have to do the job. If you ever have to remind me it's my turn to act I'm probably mid-way through Gates of Delirium!
Might be worth a try with the music of your choice. Or just try and think about anything else not related to the matter in hand.