Sunday, August 10, 2008

Magnets Inside the Body

A fair amount of my work time is spent inflicting intense external magnetic fields on patients. This is otherwise known as magnetic resonance imaging (MRI).

I therefore found it very interesting to read this interview with Quinn Norton, in the Canadian Medicine blog. Norton, a San Francisco journalist describes her experience with having a small rare earth magnet implanted into her fingertip.

Due to complications, she eventually had to have the magnet removed. In the meantime, she claimed it gave her a "sixth sense" that allowed her to detect electromagnetic fields from a distance.

As her story suggests, such implants are not not quite ready for prime time. However, it would be cool to be able to sense magnetism directly.

Anyone who has worked around MRI for very long has eventually forgotten to remove sensitive objects before entering the scanner room. At minimum, this results in having the magnetic stripe wiped on all your credit cards. Other objects, such as metal pens or nail clippers can suddenly turn into dangerous projectiles. If my finger twitched whenever I entered the scanner room, it would be a great reminder to be sure that my pockets were clear.

Internal Magnets Placed by Physicians

I don't know of any reputable physician who would implant magnets in a patient for body modification purposes. However, a cursory search of PubMed for "internal magnets" did bring up a few cases of magnets implanted for other reasons.

I found two reports (this one and this one) in which permanent magnets were implanted in the sternum to provide postoperative traction following pectus excavatum surgery.

Some cochlear implants employ an internal magnet.

I was interested to learn that total shoulder replacement by a magnetic arthroplasty has been tried in a patient with a destroyed rotator cuff. These investigators hoped that the strong samarium-cobalt magnet in the prosthetic humeral head would prevent the components from dislocating.

An anus, with homage to Kurt Vonnegut

Another group of investigators has proposed implanting strong magnets in the wall of the anal canal to prevent fecal incontinence. Their preliminary work in pigs suggests that such magnets would be strong enough to keep the anus sealed. My main worry with a magnet this strong would be how to get it open again.

Internal Magnets Removed by Physicians

What happens if you ingest a magnet? It depends.

If it's the right size, it should pass right through your system and eventually drop out in the toilet with no worries.

However, you never, ever want to ingest more than one magnet at a time. See this case report of a child who developed small bowel obstruction due to ingestion of two small (8 mm) magnets from a Polly Pocket doll (Mattel, Inc. El Segundo, CA). The obstruction was caused by the fact that when these two magnets passed by each other in adjacent loops of bowel, they were strong enough to pull these loops together. Said magnets had to be removed surgically. Eek.

Cow Magnets

I first saw the term "cow magnets" in a Gary Larson cartoon, showing several of his classic cows stuck together out in a field. I only learned much, much later that cow magnets are a veterinary device used to prevent hardware disease - bovine traumatic gastritis due to ingestion of metal objects.

Cow magnets

The idea is that after you feed one of these to an calf, it settles in the animal's rumen or reticulum and remains there for the life of the animal. The hope is that bits of ingested metal crud will stick to this magnet in a sort of a ferromagnetic bezoar, rather than causing obstruction elsewhere or perforating the animal's bowel.


Tor Arne said...

I shudder to think of what would happen if one, distraught for some reason or other, forgot about one's magnetic implant while venturing into an MRI-room, to have it ripped out of ones body. Yowza. But a cool idea nonetheless! :)

The Samurai Radiologist said...

@ tor arne:

Implanted metal can certainly be moved about in the body by a strong enough external magnetic field. Local heating is also a potential issue. However, unless an implant were really superficial or the incision site only partially healed, it's unlikely that it would actually be ripped out of one's flesh. However, one might feel an unpleasant tug. :-)