Safety of MRI scans

May 26, 2002 11:45 PM

Safety of MRI scans - annoying and temporary free registration required.
If movement whilst being scanned may not be safe, then what about the heart, lungs, blood and even a foetus? You can't keep those still.
Background: Of Mice & Magnets.
posted by southisup (12 comments total)

I realise that MRI is not a routine part of pre-natal care but it certainly is done...

Currently, little data exists to establish MRI risk for pregnant patients. Generally accepted procedure limits MRI use during pregnancy, especially during the first trimester, except in cases where the radiologist and referring physician determine that the benefit to the patient and/or fetus outweighs potential risk. (Which begs a further question: how exactly do they establish the risk?)

posted by southisup at 11:45 PM on May 26, 2002

They tell you not to move because it's unsafe? I always assumed it was because they wouldn't get a clear scan that way.
posted by CrayDrygu at 12:14 AM on May 27, 2002

er... by "that way" I mean "if you move"
posted by CrayDrygu at 12:15 AM on May 27, 2002

From the article:

A static magnetic field cannot induce electrical currents or other changes in living tissues. That 's why scanners are presumed to be safe. But as soon as an animal or person moves within a field, the field is technically no longer static. Moving fields can theoretically transfer energy to electrically active tissues, and hence influence nerve cells.

To see if strong fields would affect mice, Lockwood gave them tasty sugar water before putting them in the field. After a 30-minute exposure Lockwood found that the mice avoided the sugary substance, suggesting they associated it with having a bad time in the magnet. The effects were especially marked in animals that were allowed to move inside the field.

These animals also suffered most dramatically from "circling" behaviour. For up to five minutes after exposure, the mice would run around in anticlockwise circles. Lockwood 's colleague found that flipping the polarity of the magnet made the animals run the other way. No one knows why, but the researchers speculate that when the mice moved in the magnetic field it somehow disrupted their balance systems.

Extrapolating from rodents to people is not straightforward, but there are already signs that people who move their bodies in scanners can experience subtle symptoms. Up to 10 per cent of people scanned at field strengths of 4 tesla, which are fairly common now in research, later report a weird metallic taste in their mouth.
posted by pracowity at 1:43 AM on May 27, 2002

A weird metallaic taste may be a normal reaction but does it mean that it is a cause for alarm? Any studies done on the zillions of people thus far scanned? My son took part in a study done at Yale and was put in FMRI a few times with thus far no effects that I have noticed. But then damage could in theory have been done that was not detected by me.
posted by Postroad at 3:24 AM on May 27, 2002

Does your son run around in anticlockwise circles?
posted by pracowity at 3:59 AM on May 27, 2002

It's impossible to stay perfectly still. Figure, your body is always in motion, blood pumps through veins and arteries and capilaries, you blink, repirate. On a microscopic level, what's the difference between that and turning your head 90 degrees?
posted by Modem Ovary at 4:12 AM on May 27, 2002

Let's look at this in context. Medical imaging is not without risk. Plain X-Ray uses, well, X-Rays, so does CT scanning even the new spiral models that are trendy for "health-scanning". Other imaging techniques inject short half-life radioactive isotopes to expose the imaging film. MRI is simply one more way. Totally safe? Perhaps not, but certainly no less safe than the other techniques.
posted by shagoth at 7:36 AM on May 27, 2002

When I cracked my skull open, I was MRI'd. And although I now have an alarming tendency to make right-hand turns by executing three consecutive left-hand turns, I'm glad I got it; without the MRI results, I'd probably have been released from hospital with a gaping hole in my head...
posted by five fresh fish at 8:34 AM on May 27, 2002

I think shagoth's right. The real question: is this procedure more dangerous than ignorance?
posted by NortonDC at 8:55 AM on May 27, 2002

The real question: is this procedure more dangerous than ignorance?

That is indeed a major question in life.
posted by HTuttle at 10:25 AM on May 27, 2002

useful links: MRI Safety
and current uk guidelines (recently updated, can't find an online version though)

So far, no long term adverse effects have been noted, although the obvious benefits of MRI has to be weighed against the uncertain and therefore unquantifiable long term risks, plus the known and documented short term risks

btw, spiral CT aren't just 'trendy for "health-scanning"' - its the gold standard investigation for several lung conditions, such as pulmonary embolism

posted by navin at 11:48 AM on May 27, 2002