Question: Helllo Andy have you ever had a MRI failure by accident, if so what can happen to the person being scaned?

Andrew Scott answered on 18 Jun 2015:

Having an MRI scan is very safe. The main danger is from flying iron objects. Before you go into the room with the scanner you need to remove all metallic objects from your body. The huge magnet in the MRI scanner pulls iron objects out of your pockets or hands and they go flying into the scanner. A small boy died in the USA a few years ago when someone took an oxygen cylinder near the scanner. Thankfully this doesn’t happen very often, although I have worked places where there have been a few near misses. I’ve heard of coins flying out of people pockets, medical equipment getting stuck in and the most common one is a floor polisher, when no one has told the cleaner that they can’t take it in the scanner room.

The other problem is from wires or bits of metal getting hot. If the wires are the right length they can absorb the radiowaves that we use to create pictures and cause burns. This is very rare.

These things haven’t happened to me, although we did once have to go to test a new scanner on a building site where we had to wear steel toe cap boots. I kept kicking the scanner when I walked past it because the steel toe cap boots were attracted to the scanner.

The other problem with the magnet in the scanner is that it is a superconductor. This means that the metal coils of wire inside are cooled to -270degrees C using liquid helium. The wire has no resistance at this temperature so we don’t have to connect it to the electricity supply to keep the magnetic field. The issue is that you can’t remove the magnetic field without boiling off all of the liquid helium. This is called a quench and is very expensive because it can damage the coils of wire. Liquid helium is also very expensive because there is a shortage of helium, because it’s all been used up in helium balloons!