MRI - Is it safe?
Dr Richard Watts from the Department of Physics and Astronomy at the University of Canterbury and Rebecca Tunnicliffe of the Van der Veer Institute for Parkinson’s & Brain Research talk about MRI safety.
DR RICHARD WATTS
It’s not a procedure that’s painful, or uncomfortable, or is associated with any risks so, essentially you’re getting some images of your brain and with very little risk or discomfort involved in that. As far as we know there are no ill effects of MRI scans at all. The main safety things which we’re concerned about, just come from the fact that you have a very strong magnetic field there, and that will tend to pull things into the field. So we’re very concerned about what you take into the MRI scan and the harmful effects which we’ve had from MRI, have come from accidents where people have taken in things like gas cylinders, or other bits of metal into the MRI scanner, and these things will be pulled in and they’ll travel very fast by the time they hit, by the time they get into the bore of the MRI scanner. Most of us can have an MRI scan. The main things which prevent you from having a scan would be if you’ve got bits of metal in your body.
So when a patient would arrive in the department, they’ll be asked to fill out a safety checklist – so on that is a number of questions such as, do you have a cardiac pace maker? Have you had aneurism clips? Previous medical history which is relevant to our scan. So things like a cardiac pacemaker would prevent them from having an MRI scan. But anything that’s embedded in bone is calcified so it can’t move, so that’s fine, that wouldn’t cause us a problem at all. Something like an aneurism clip, some of them are absolutely fine to go into the scanner, these are surgical clips that are placed on blood vessels within the brain. Some of them aren’t ok, and they potentially could move, they’re not gonna be ripped out of the head or do any sort of bolts of lightening, nothing like you see on TV, but what it will do is it can move off the blood vessel that will cause the blood vessel to bleed. The whole reason that it was out on in the first place, was to stop that vessel bleeding. So that’s why we ask all those safety questions and go through them, and no patient enters the scanner until we’re 100% satisfied they are safe to go into the scanner.
DR RICHARD WATTS
Bits of metal, they also tend to distort the magnetic field so for instance if you’ve got a pin in your leg, while that might actually be safe to be scanned, it’ll distort the magnetic field around that part of your leg and it’ll make the images not so good there. Having said that if you’ve got a pin in your leg, we may still be happy to scan your brain. It can be a little bit tricky if you’re imaging either very young children or you have somebody who’s maybe in pain, who finds it difficult to hold still.
MRI is generally, relatively slow. We produce images over a period of a few minutes. It might take three, four or five minutes to generate a set of images. So if you can’t hold still over that length of time then it gets more difficult and we get essentially a blurring of the images and it reduces the accuracy. But as far as safety’s concerned, we’re not using ionising radiation, so as far as we know there’s no way that this kind of technique can cause chemical changes, can actually cause damage to the brain.