I'd never heard of getting an MRI on the bowel but found this
http://www.radiology.ucsf.edu/patients/mr_enter theres a bit of info there.
I've have had MRI scans done before on my hips - be warned MRIs take a loooong time and you literally can't move as it messes up the pictures. I would have thought as the bowels are moving all the time it would mess it up but according to the info in that link they stop them from moving.
Maybe someone else here will have had it done and be able to offer their experience.