Yeah, so I've personally stuck my hand in an MRI without incident; however at the time I only had a V&P in that hand. Of I course I now have muliple M31s, but haven't been in the MIR room with them. I have a friend with an M31 who went into the MRI room today and states that it caused excrutiating pain. The site is also significantly swollen.
I would advise at the very least wrapping the finger or area tightly with a medical tape prior to having an MRI if possible. The bracing should be adequate to prevent any serious tissue damage. If I'm wrong... I'll let you know as soon as I get a chance.