Someone’s uploaded a video which serves both as an important teaching aid for MRI brain scanner safety and a wonderfully entertaining guide to the destructive power of a magnet the size of a small car.
The video itself is a a little bit old, and so has a sort of B-movie quality to it, but which makes it all the more fun.
However, it contains the classic sequence, part of virtually every MRI safety video, where technicians release a steel wrench near the magnet, which then flies through the air and obliterates a number of destructible objects in its path.
The magnetic field is designed to focus on a very specific area, and that’s where your head is placed when you’re scanned.
Any ferrous metals in the room will be drawn towards the centre of the field, probably at speed, which can be quite unfortunate if your head is occupying the same position.
We collected some nice examples of objects stuck in scanners earlier in the year, including chairs, oxygen bottles, and other assorted medical equipment.
If you want to see the sort of force generated by a steel oxygen bottle heading towards the centre of an MR magnet, there’s a short (and somewhat frightening) video on YouTube of some brave MRI technicians demonstrating the effect.
Unfortunately, this is exactly what happened in one tragic case where a six-year-old boy was killed. The incident is now also a standard part of MRI safety training.
However, the danger isn’t only from the ‘missile effect’. Additionally, elongated ferrous objects will try to align with the magnetic field. This is a problem if you have metal implants in your body.
For example, brain surgery to prevent aneurysms (strokes) often involves putting a small metal clip over the blood vessel to clamp it shut, to prevent blood flowing to the burst or weakened area. Nowadays, these clips are not ferrous, so aren’t a problem, but older ones might be affected by magnets.
Having a ferrous metal clip suddenly move inside your head can be disastrous, as it has the potential to shear the blood vessel, causing internal bleeding.
The video also talks about other sorts of possible MR hazards, largely involving the liquid helium and nitrogen boiling off and freezing, poisoning or pressurising the surroundings.
An explosion of an MRI magnetic when the gasses boiled off too quickly was caught on video by a TV news crew which creates quite a spectacular effect.
However, do bear in mind that these incidents are few and far between. Having an MRI is significantly safer than crossing the road.
If you go for an MRI scan, you’ll likely be interviewed and / or examined to make sure you have no metal in your body, and you’ll have all metal removed from you.
If you want to try, you can volunteer for brain scanning experiments where you’ll usually get a small payment and a picture of your brain – contact your local university or teaching hospital.