|By lululemon athletica|
(Flickr: Yoga Journal Conference)
[CC BY 2.0], via Wikimedia Commons
I kicked off today's lecture by looking at magnetic field strengths, what's the earth's magnetic field (5 μT) or of a refrigerator magnet (5 mT), compared to the superconducting magnets used in NMR, which are on the order of 10T. (1T is one tesla.) This led to a quick review of the risks in MRI, which aren't about the energy of the radiation used (which is billions of times lower than X-rays), but more about the interactions of the high magnetic fields, the radiofrequencies and metals.
A hand shot up and student who is an EMT describes a patient whose tattoo started burning during an MRI. I pointed out this is a known phenomenon, and while most inks don't pose an issue, it should discourage you from DIY tattooing. Then a student asked, "Is it true you can't wear lululemon pants when you have an MRI?"
I admitted this was out of my zone, but promised to follow up.
I can now report that yes, wearing lululemon pants — or any clothing with metallic microfibers, such as those great antimicrobial t-shirts — in an MRI can lead to serious burns, particularly in patients that have been sedated or are otherwise unconscious and unable to signal their discomfort. Even non-ferromagnetic materials presents problems in the MRI as eddy currents can develop around them, creating little induction heaters. Loops of all sorts, even skin to skin contact between a patient's own body parts can lead to heating and subsequent burns. And tattoos with large loops in them? They can heat as well.
Other things I learned this afternoon. You can levitate a frog with a 16T field (thank you Wikipedia), and neutron stars have magnetic fields on the megaTesla scale.