I suspect it would be bad.
A large ball bearing is heavy, and has a lot of surface area, so it may not do that much damage. I think the stomach is pretty tough, so if its in there, maybe it just hurts, but doesn’t seriously damage the tissue. Not sure where the most sensitive tissue is in the digestive tract.
Were you planning on doing this soon?
Oh yeah, ball bearings are usually stainless steel, which may not be affected much by magnetism. Ceramic ones not at all.
It would rip out of your body, and lodge into the side of the MRI, leaving a gaping hole in the side of your stomach… If you happen to get the MRI outside a hospital (for some reason), you would probably end up dying from the injury…
That answer your question?
ETA: TriPolar brought up the point about it not being that magnetic, if the ball bearing wasn’t magnetic, then ignore what I said… However, if it is, my statement stands. MRI’s involve some REALLY powerful magnetic fields.
:dubious:
The magnetic fields in MRI machines are pretty intense. I suspect it would be bad too.
ETA: Probably in the way that Hirka T’Bawa said. (How come I didn’t see that answer?
) Anyway, why would stainless steel not be magnetic? I am pretty sure it is. It is mostly iron.
The addition of chromium does something (I don’t know what) that neutralizes the ferromagnetism in iron. Different alloys are affected in differently. For ball bearings I suspect you want an alloy which is not attracted to bits or iron that would cause wear.
Also, I don’t know what was meant by large. I’ve seen ball bearings up to 1" diameter. They probably get even bigger. But they are also heavy at that size. If it’s that large, and it has no sharp edges, it’s not going to accelerate that fast. Suppose you put a 1" ball bearing on your stomach (on the outside) and pressed down on really hard. It might hurt a lot and leave a huge bruise, even damage tissue, but I have a hard time seeing it penetrating through the muscle layer.
Ball bearings can get much smaller. Those are the one’s I’d worry about. It’s one of the reasons I don’t swallow ball bearings.
Here’s a link to some info about stainless steel and magnetism. Looks like nickel is the big factor in magnetic properties.
Honestly, I wouldn’t be worried as much about the muscle layer, I would be more worried about puncturing a hole in the stomach and letting the stomach acid out into the body cavity… There is a reason that Ulcers used to be a major cause of death.
That’s another reason I don’t swallow ball bearings.
You get MRIs frequently there TriPolar?
I’m no materials engineer, but I’ve rebuilt enough bicycles to notice that ball bearings indeed rust so I checked up on ball bearing manufacturing. According to this site, the most common steel for ball bearings is 52100 which is indeed magnetic.
The magnetic fields in an MRI aren’t going to launch the bearing out of your body; MRIs use rapidly oscillating fields, not strong monodirectional fields, which will cause small mechanical vibrations and possibly significant heating of any metallic objects present. For the ball bearing case, the vibrations are unlikely to be significant but the heating could be harmful. In addition, the presence of large amounts of ferromagnetic material will cause artifacting on the scan, seriously impacting its diagnostic usefulness.
My son has regular surveillance MRIs of his head and spine because of his NF1; prior to one of them, some time back, he had (without our knowledge) swallowed two small metal objects. When the scan reached his abdominal region, the technician noted artifacting and aborted the remainder of the scan and sent us upstairs for an X-ray which identified the objects. They passed harmlessly in his stool a couple days later.
The heating effects can occur with nonferrous metals as well, so just because the ball bearing is a relatively nonmagnetic type does not necessarily preclude injury.
Have you not heard of some of the heinous MRI accidents involving metal objects being propelled with great force and speed? Here’s an NYT article documenting some of them. There have been severe injuries and deaths because of these types of accidents. Google “MRI accidents” for more pics and articles.
Yes, the ball bearing (assuming it’s ferromagnetic) will be pulled with great force. The force will be proportional to the cube of its diameter, and the resistance of your flesh will be proportional to the square of its diameter. I can’t say whether it would tear your flesh, but if it doesn’t, it’ll pull your body along with it.
My stepfather is a radiologist with an expertise in magnetic resonance imaging, and (as I said) my son has regular routine MRIs. I’ve reviewed the literature and expert advice on MRI safety extensively and have access to experts on this issue, and while I can’t explain the physics (not right now at least) there is little or no risk, based on reported experience, that a small bit of metal in the body would be “flung with such force” as to be pulled free. There are, reportedly, incidents where people with bullets left in their bodies who have had them dislodged and moved a short distance during an MRI, causing injury; this can be quite dangerous if the bullet is near a vital structure (which is often the case when a bullet is left unremoved).
This is probably because the patient is in (or near) the center of a focused field, while the objects that are being launched are, well, not.
MRI scanners use static fields in the range of 1.5 to 3 T. That is a huge field strength. It is orders of magnitude higher than the strength of the gradient coils that are driven during the scan. Indeed ordinary steel saturates at 1.6T. (To put the gradient coils in perspective, the favourite driver for the coils in early research scanners was a Crown HiFi amplifier.)
My father likes to tell the story of how one day working with a newly installed MRO scanner he forgot that he had a pen in his pocket. The only bit of metal was the clip. But the magnet picked it out of his pocket from across the room, and cheerfully floated it across.
The main magnet is pretty close to a dipole, and at a distance the magnetic field strength drops as the cube of the distance. However these a huge magnets, and closer to them you are going to see less fall off. The magnets are designed to maintain that 1.5-3T field strength right with as high a homogeneity as the manufactures can manage right across the main part of the tunnel. Until you are at least the width of the tunnel away from the tunnel it won’t be behaving much like a dipole.
At these field strengths the permittivity of steel is much higher than at low fields. The strength of the induced field created in the ball bearing may be remarkably high.
Along with Darryl L., I question this. Here’s a site that has this to say:
I’m sorry, KellyM, but you are wrong. From the article that Machine Elf linked to:
I suspect that a “metal aneurysm clip” is roughly the same size as a smaller ball bearing, and it was moved enough in her brain to kill her. Now, I know the brain is a lot more mushy than the abdomen, and injury there is more serious, but the point still stands that an MRI is more than capable of moving a small piece of metal inside the body.
In your first post, you said:
And you are half right…there is a rapidly oscillating field, that is produced by the graident coils, however there is ALWAYS a very large magnetic field produced by the main magnet. It is a superconducter, cooled by liquid helium with backup systems and cannot, under normal circumstances, be “turned off.”
And while there can sometimes be heating of small metal objects through induction (especially if they are circular, like a pacemaker and it’s lead wire,) this is actually caused by the RF coil, not the magnets.
Well, according to House, it will tear a bullet out of a body.
This is a pretty good indication that it actually won’t do much of anything.
I have some metal staples in me and when I had an MRI the techs made me ask my surgeon what they were made from (titanium) before they would perfrom the MRI.
Whether the techs were uninformed or not, I cannot say.
While most implant metals in recent years are made from non-ferrous metals (titanium being among them,) good techs are always rigorous in finding out just exactly what is inside you to be as safe as possible.
The interesting thing is that even though the staples are safe for the MRI, if you had to get an MRI near their location, they would still cause trouble by interfering with the RF coil and causing artifacts.
An aneurysm clip holds part of a weakened blood vessel to keep it from bursting. That blood vessel would probably fail if the clip was moved a very slight amount. The cite isn’t specific, but it only says that the clip was “dislodged”, which probably means it moved just enough to cause a sever hemorrhage. It probably wasn’t ricocheting around the brain case.