Why is it bad to put metal in an MRI machine?

[pa5tabear]

I saw a House episode where a person had internal bleeding because they had metal inside their body and they went into an MRI machine.

I'm learning about NMR now and I want to try and understand it more.

 

[MostlyHarmless]

MRI stands for MAGNETIC resonance imaging.

http://en.wikipedia.org/wiki/Magnetic_resonance_imaging -First google result, second paragraph first line.

"An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetization of some atomic nuclei in the body, and radio frequency magnetic fields are applied to systematically alter the alignment of this magnetization."

 

[pa5tabear]

MRI stands for MAGNETIC resonance imaging.

http://en.wikipedia.org/wiki/Magnetic_resonance_imaging -First google result, second paragraph first line.

"An MRI scanner is a device in which the patient lies within a large, powerful magnet where the magnetic field is used to align the magnetization of some atomic nuclei in the body, and radio frequency magnetic fields are applied to systematically alter the alignment of this magnetization."

Ok. So what about the metal makes it respond to a magnetic field?

 

[MostlyHarmless]

Check out this link, it might be helpful. http://science.howstuffworks.com/magnet3.htm

 

[akdude1]

MRIs use magnetic fields up to 20,000 times the Earth's magnetic field in other words that's a freaked powerful magnetic field for example if you had earrings in while you entered an MRI machine and they turned it on your ears would be done for.

 

[Dale]

Ok. So what about the metal makes it respond to a magnetic field?

The metal is ferromagnetic. The same property that makes it so that magnets can stick on metal refrigerators. Just like there is a force exerted by a magnet on a refrigerator, there is also a force exerted by a MRI system on a ferromagnetic implant. Depending on the magnitude of that force and the strength and importance of the tissue nearby, the consequences can be disasterous.

 

[Q_Goest]

Note also that the problem with metal near an MRI is only magnetic metals such as steel. The magnetic field produced by the MRI is strong enough to lift hundreds of pounds of magnetic material, so if you had a chunk of magnetic material inside you, it would be pulled into the MRI without you!

For non-magnetic metals such as aluminum, copper, austenitic stainless steel, titanium, etc... there is no problem with having them near an MRI.

 

[BruceW]

yeah, that's true. Although I would still be cautious, to say the least! for example, if I had some metal that I thought was pure (and non-magnetic), but it turned out to be an alloy of some kind, containing some traces of magnetic elements.

 

[CWatters]

http://www.aboutsafety.com/article.cfm?id=1100

A six-year-old boy undergoing an MRI examination died after the machine's powerful magnet pulled a metal oxygen tank through the air, fracturing his skull.

an MRI magnet pulled a gun out of the hand of a police officer and the gun shot a round that lodged in a wall.

 

[CWatters]

See also videos on Youtube..

 

[A.T.]

Also be careful with tattoos:

http://www.ajronline.org/doi/abs/10.2214/AJR.06.5082

 

[Dale]

For non-magnetic metals such as aluminum, copper, austenitic stainless steel, titanium, etc... there is no problem with having them near an MRI.

Even with non-ferromagnetic materials you can get forces due to eddy currents, but I have never heard of an injury due to this. It is kind of a cool effect to see, I used to show it to tour groups. I would take an aluminum safety sign, and try to wave it back and forth through the field, etc.

 

[A.T.]

Even with non-ferromagnetic materials you can get forces due to eddy currents, but I have never heard of an injury due to this.

See the link about tattoos I posted:

identified the cause as originating in a locally induced electric current. This can, generically speaking, be induced by any metal (not just ferromagnetic metals) moving through a high-frequency magnetic field

Read More: http://www.ajronline.org/doi/full/10.2214/AJR.06.5082

 

[BruceW]

soo... the take-away message is that magneto (from the x-men franchise) is a lot more dangerous than I had previously thought? hehe

 

[A.T.]

soo... the take-away message is that magneto (from the x-men franchise) is a lot more dangerous than I had previously thought? hehe

Iron Man is so screwed...

 

[Q_Goest]

Even with non-ferromagnetic materials you can get forces due to eddy currents, but I have never heard of an injury due to this. It is kind of a cool effect to see, I used to show it to tour groups. I would take an aluminum safety sign, and try to wave it back and forth through the field, etc.

Interesting. I do a lot of work for MRI manufacturers and as long as the materials we use for the equipment we design are non-magnetic such as austenitic stainless and aluminum, we have no problem with them. Does the effect you're mentioning only apply to things that are moving? All our equipment is generally stationary (or moving slowly) when connected to the MRI.

 

[Dale]

Interesting. I do a lot of work for MRI manufacturers and as long as the materials we use for the equipment we design are non-magnetic such as austenitic stainless and aluminum, we have no problem with them. Does the effect you're mentioning only apply to things that are moving? All our equipment is generally stationary (or moving slowly) when connected to the MRI.

Yes, only moving metal feels this force from the main field, and even then it is only significant on large sheets of metal where the induced eddy current loops are large. That is why I always use an aluminum sign.