If you aren’t comfortable with it, don’t do it, unless of cause this is a study you really would like to support.
I haven’t heard of any health risk in connection with the magnetic field in a MRI. There are risks if you have metal fragments in your body, especially near your eyes. If they want to inject you with contrast I would on the other hand be more concerned with this, then the MRI itself. This can cause an allergic reaction. It can be easily controlled with drugs, but who wants to go there?
Also if you have a problem with small spaces they might or could give you a sedative, but again as this is the alternative board, who wants that?