mr phys:Can I coin 'stuck' to the wall of an MRI be removed?

mrphys · Joined: 12 Sep 2008 Posts: 8

Well, This type of experiment (with the coin) I wouldn't do. But what is the best way to determine what is mr compatable/safe?

What metals can and can't you bring into the MRI?
Can using a simple fridge magnet be enough to determine object safety? Smile

Is there any way at all of having some type of mechanical 'motor' inside the MRI? This could be usefull for doing experiments with moving objects/fluids.

Thanks

tgilk · Joined: 13 Sep 2008 Posts: 2

OK, first, depending on where your are, your coins may not be significantly ferromagnetic (US coins are made almost exclusively from non-ferromagnetic materials, but Canadian and Mexican coins, however, have magnetic materials).

Second, testing the magnetic nature of materials with a fridge-door magnet is imprecise, to say the least. To stick to your fridge door, that magnet needs to have s surface magnetism of around 75 gauss or greater and drops off at the cube of the distance. You may test an object's magnetic nature with that fridge-door magnet, but you will only be testing the very surface of the object with the maximum possible strength of the fridge-door magnet. If the surface of your object-to-be-tested is non-ferromagnetic, your fridge-door magnet could indicate that the whole object is safe in the MRI when there could be ferromagnetic materials below the surface that the magnet wasn't noticeably attracted to.

MRI facilities, when they test the magnetic properties of materials to determine if they can be brought near the MRI use magnets that are up to 1,000 gauss. Additionally, a number of professional bodies have recommended that MRI facilities use a new breed of ferromagnetic detectors (see http://mrimetaldetector.com/blog/ ). This is because materials that are ferromagnetically 'weak' or 'hard' (meaning either not capable of being significantly magnetized or require a more powerful magnetic force to induce significant magnetization) can still be very dangerous in the MRI environment. To compare, your fridge-door magnet may be up to 150 gauss, whereas an MRI may be 15,000 or 30,000 gauss. Objects that don't respond to your little magnet may be dangerously attracted to an MRI.

To your question about machines in the MRI, there are very few machines that are designed and tested to work inside MRI's. The profound magnetic fields make any sort of electromechanical device problematic. There is a new pneumatically-activated robot that has been designed for use inside the MRI scanner, but don't go looking for it at Radio Shack.

I hope this helps,

Tobias Gilk, M. Arch.
President & MRI Safety Director
Mednovus, Inc.
_________________
Please feel free to contact me through our websites http://www.MEDNOVUS.com or http://MRImetalDetector.com/blog/