I have never had an MRI done for ferriscan, so maybe I am not the best person to reply, but I have had a CT Scan done that involved my head and neck. I didn't think I was claustrophobic, but once your in there it is a bit nerve wracking (especially with the noises the machine makes). I don't know if all places do this, but the hospital I was seen at had a mirror attached to the machine, and recommended looking at it to see out if the patient starts feeling closed in. I glanced at it once on my way in and thought it wouldn't help me, lol.
Best advice I can give - close your eyes, before you even go in, CLOSE YOUR EYES! If you do not see the walls of the machine around you I think it makes a big difference. Close your eyes before they start moving the table and then keep them closed until they take you out. I think there is great power in what we can see, I realize not everyone is this way and just the thought might be too much, for me closing my eyes got me through it easy peasy! Also if the noise bugs you (and it probably will at some point even with earplugs in) pretend your at a construction site, also easier to do with your eyes closed, lol.
Best wishes!