How do CAT scan operators deal with dental braces?

I watched Allan Alda’s Scientific American PBS’s show and it informed that braces could be torn out of teeth if one had them while under a CAT scan. I remember a case where an oxygen cylinder jumped and killed a kid that was being examined in one of those machines; so yes, those things have a nasty magnetic field.

The PBS show made the comment about braces when a kid with them was being tested in a mock MRI; later, there was no obstacle to take a scan in a real machine. Other sites on the web claim that braces are no problem for an MRI, so what is the deal here?

Are you sure you don’t have it backwards? It’s my impression that you can’t have metal with an MRI. CAT (also known as CT) scan is pretty much just a 3D x-ray.

MRI would be the one with a problem with metal. IIRC some things are okay. I belive screws in bones from previous surgeries are ok in some instances, but staples in your skin could be pulled out. Again IIRC small bits of metal that are very firmly in place are ok but but things that are not as firm are a problem. I think it is taken on a case to case basis.


Ok, disregard CAT scan; the question, now regarding ONLY MRI’s, still stands though.

I just did some minor looking around on the web and it seems that braces and fillings should be ok but may cause distortion of the facial images, same for prostetic hips as long as it is atleast a few weeks post surgery. Problems still seem to lie with things that are not firmly in place, one thing that was mentioned was bullets that are in the body, I would also assume shrapnal(sp?). Another things I forgot about was people that work in machining shops that may have small metal filings in there eyes. These filings could be pulled through the eye which would clearly be a cause for concern. If this is the case, I think they will give you a normal x-ray first to look for any problems. If you want to look for more do a seach for MRI and METAL.
Here’s a picture I always liked

IANADoctor, but I believe most metallic things they put in people’s bodies are made of stainless steel, which is nonmagnetizable (is that a word?). The company I work for, which builds RF generators and power delivery systems for thin-film manufacturing, uses stainless steel screws in places that carry RF current for the same reason.

Well, I had a CT scan this morning and they made me take my earrring out… Did they really need to do that?

You probably didn’t have to, but the machine wouldn’t be able to “see” through them.

And it’s probably better to simply remove the earring instead of having everyone who looks at that x-ray say “what the hell is that on the x-ray?” and have to figure it out.

Well, I have a metal plate and a bunch of screws in my left leg. When my ortho doc wanted to do an MRI to see what else was going on down there, he had to settle for a CT (which doesn’t do as good a job showing soft tissues) because of the plate. I’m not sure whether it was because of possibility of injury to me, or problems with imaging ability due to the distortion caused by the metal, or both.

I believe that some grades of SS are magnetic, so that’s not always true… although I would suspect you’re correct that the ones used for braces and such (if it is indeed SS) aren’t.

Not so sure CAT scans never refer to MRI. CAT stands for Computerized Axial Tomography. Literally, MRI scans are computerized, and they produce tomographs that include axial views, right? Since X-Rays were the first common axial imaging means, CAT scans were originally X-Ray based - but are they necessarily still always X-Rays?
MRI scans necessarily use Magnetic Resonance, or Nuclear Magnetic Resonance (the original term still used by physicists). So no question MRI scans have nothing to do with X-Rays.

CT scans are totally different from MRI scans. CT scans uses x-rays and MRI do things with the water in your tissues. Also, AFAIK, all stainless steel is ferromagnetic.

As a metallurgist, I have to jump into the fray wrt stainless steel. Stainless steels are an alloy family and the only restriction in the alloy is it is Fe with ~13 weight percent Cr. Some stainless alloys are ferromagnetic (the electrons exchange couple and form in domains (where the moment is in one direction)). Other stainless alloys are paramagnetic (no exchange coupling, no domains, and the magnetic field that aligns the spins (what MRI does) has no lasting effect once the field is removed. In ferromagnets (Fe, Co, Ni) the applied field causes a torque on the FM body M cross H – this torque is the MRI problem.

Also. Non-magnetic stainless steels can also have magnetic precipitates if they are worked improperly. I have had significant problems with our machine shop working stainless for fixtures to place in high magnetic fields. They are fine after the working, but over a period of a week, ferromagnetic precipation occurs, making them unsuitable for high field fixtures.

IANAD, but I do have radiology experience. (Also, Rysdad is going through radiography school, and can answer this question as well.)

It is entirely possible for magnetic metal to cause damage to the body during an MRI scan. For this reason, some radiologists will order plain-film X-rays to be done prior to an MRI to determine if there is metal in the area to be scanned, where it is, and if it will cause problems with the scan. The most common is a skull study for patients with a history of metal exposure (welders and the like, who may have metallic particles in their skin or eyes).

It’s also possible for foreign objects in the scanning room to be attracted to the magnet, causing damage to the equipment and/or patient. Police escorting criminals have had guns discharged, and a boy was killed when a magnetic oxygen tank hit him during an MRI. (That link also has more information on MRI accidents in general.) Techs working in the MRI room don’t bring anything in there with them, and some of them have scrubs without pockets so they can’t bring something in by mistake.

That being said, there are usually other imaging techniques that can be done in patients with metal. CTs, plain-film studies, fluoroscopic studies can all be done, should the need arise.