There actually was a guy who wore a buttplug with a metal core in an MRT. The plug shot through his body like a high velocity bullet and was stopped by his sternum. He survived with severe internal injuries and sued the company selling the plug.
People like that guy is the reason some MRIs require you to walk through a metal detector first. People are stupid and will ignore safety measures all the time.
I had abdominal surgery several years ago and the surgeon mentioned that they left some clips inside. To this day I have no idea if they are magnetic or not.
If the coins are magnetic that's what would happen. But if you're going to violently tear a hole in your abdomen, the hospital is where you want to do it. I'd say there's a fair chance you survive and live a medically complicated life
I have shrapnel in my leg, it's copper and brass, and I have had MRIs with no ill effects. Fucks up some CAT scans and xrays, but only if they are scanning that leg. It's so small, though, that modern metal detectors don't register it anymore.
If it's magnetic resonance imaging, then if your magnetic resonance matches the MRI's, you'll just shatter like an opera singer breaking a crystal glass.