Hi Fenderman,
I've had at least 8 prostate mpMRI scans in the last 7 or 8 years and most of them have been done with my head still out or just out of the machine (I.e. they put you in feet first).
Only the last couple have been done the other way around and although I wondered why, as it didn't bother me, I didn't ask.
My point is, they can obviously do a feet first mpMRI and so surely given your claustrophobia, if they're aware of it, they'll do it that way.