I worked in the first outpatient MRI clinic in Portland right out of college.
Amazing tech.
If you are the least bit claustrophobic, ask for a shot of valium. It will help.
Think back on your work history. If you have ever worked around metal, grinding, welding, etc. Be sure to disclose it. You can have tiny tiny slivers of metal in your eyes and skin that could be torn out of you during the exam.
Remember, this is a giant powerful magnet. If you have metal in your it will be pulled out.
A few weird things I saw...
Old dude was in a submarine in WWII that was hit by a depth charge and started sinking. They were barely able to save the sub and crew. He didn't think he'd have a problem being instead the MRI, as soon as he was slid inside it all came back. He had a complete breakdown. I felt really bad for him.
Another guy forgot he had shrapnel in Vietnam, as soon as he walked into the room he could feel something moving under his skin.
I've heard stories of employees bringing regular wheelchairs into the MRI room instead of the all-alloy ones and those get smashed and sucked right into the machine.