I feel like I'm being eaten by a thousand million shivering furry holes

[venta]

Off to the hospital for another MRI this morning (we're on day 19, if you're following along). If you want to really confuse hospital staff, turn up wearing an extravagant legbrace when they have an instruction to MRI the other leg.

The same radiographer saw me. We went through all the questions again, checking that I don't contain implants, metal plates, or shrapnel (if you're not aware: MRIs are giant magnets and getting metal anywhere near them is various different kinds of disastrous). As before, jewellery off, legbrace off, hairslide off. Would the neoprene support I was wearing around the knee she was scanning be a problem? It would not, and she settled me into the same dinky turquoise little machine.

Two minutes later she was back. The machine is apparently temperamental, and was showing no pictures. Could I shuffle out while she made a technical adjustment?

The answer turned out to be no. I could not. I initially thought my knee support had caught on something, then realised that actually the magnetic field was fiercely hugging my knee and refusing to let it go.

Oops.

With a certain amount of fighting I won and regained ownership of my leg. I removed the support, and apparently the pictures miraculously popped into being.

Oops. I apologised. A lot. (She was very nice about it.)

Back home, I checked the box the support came in (which for no obvious reason I insisted on keeping "in case"). Fibre content: Neoprene 62%, Polyester 20%, Nylon 17%, Spandex 1% (washable 30°). Nowhere on the box does it say that it has any metallic content. Although it does have some sort of internal structure to give it rigidity, when I'd considered it this morning while dressing I was certain it was non-metallic.

So, today's take-home lesson: do not wear a Boots Advanced Adjustable Knee Support for an MRI.

Comments

[lnr]

Gosh that's a bit alarming. You'd think the radiographer might have been aware?

Worth telling Boots?

[venta.livejournal.com]

Given the whole "arrgh, no metal, get that hairslide out!" attitude she was surprisingly unworried about the whole thing. Once I'd taken the support off, she looked at it and she seemed to think the structure was metallic in nature.

I might contact Boots, partly because I'm curious about what's in there! Just need to work out how to phrase a message to them so I don't sound like a whiny person wanting compensation for magnetic trauma!

[sushidog.livejournal.com]

Having worked with MR scanners, I would say yes, do contact Boots; they really ought to have a warning on there!

[venta.livejournal.com]

OK! That sounds like expert advice :)

I've dropped them an email. Although their "are you sure you've read the FAQ, here are some possibly related queries" turned up some pretty peculiar suggestions!

"Hi. Your knee support nearly made a magnet pull my leg off!"

"Have you considered reading: 'why didn't my voucher code activate at checkout'?"

[sushidog.livejournal.com]

Oh, and also, did you need a Lullaby to soothe you while they looked to see whether there was a Cure for your knee?

[venta.livejournal.com]

Nice!

Also, one kudo to you :)

[drdoug.livejournal.com]

I've worked around big magnets too (NMR spectrometers) and I can understand why she was unworried at that point.

There are two things to be very scared of with rogue metallic objects when operating big magnets: damage to the machine, and damage to anything between the rogue object and the machine. Which in MRI situations is often the patient - the field in the cavity isn't homogenous, so a rogue object can flip around in there causing damage on multiple passes. Oh, and this is assuming, of course, that the object itself isn't something you care about - which will generally be the case if you are a large-magnet operator.

Once something is stuck steadily to the inside of the magnet, the scary bit of the operation has passed - and in this situation, without serious incident. If nothing is moving, there are no problems. Or no further problems, if something was flying around but has now stuck. The risks the operator needs to be scared about are gone, and they can deal with the aftermath calmly.

It's a bit like the way security screening people are pretty frosty when your baggage sets off the alarms, but as soon as they find the rogue fork/snowstorm globe that caused the alert, they are (sometimes!) more relaxed and even friendly.

[drdoug.livejournal.com]

... and, of course, she'd just had a very simple explanation for why the machine was playing up, and one that was readily fixable. That will have tended to make her chipper and relaxed.

[venta.livejournal.com]

At the stage when she thought the machine was at fault, she said "hopefully we won't have to turn it off - though this one doesn't take too long".

I thought one of the big problems with MRI machines was that it took a long time to shut them down (in a non-emergency scenario) and to start them up again. I wish I'd asked her how long it would take. I probably would have done had I not been distracted by it demonstrating a fond attachment to my leg.

[feanelwa.livejournal.com]

There are different kinds of shutdown. She may have initially thought the computer wasn't talking to the detectors properly and just wanted to restart it, which is a problem I've had with various microscope bits. If you turn all the magnets off and back on it's a rather long proposition because you have to give it time to get over its hysteresis as the current comes back in the coils and get to a stable field again. Electron lenses are enough of a pain in the ass that you want to leave them at least overnight after you turn them on; I'm not sure how an MRI would scale because the field and the polepiece gap are bigger but the resolution you need is somewhat less fine too. But I wouldn't be surprised if it was longer.

[venta.livejournal.com]

Wow. Given the small readership of this LJ, three people who professionally know about big magnets is quite impressive.

I had a cursory Google this morning, and saw people quoting a week to bring the full-on coffin-like MRI machines into working order; that seemed to be all about getting the superconductors down to the right temperature, though. (Which is presumably necessary before you can expect the machine to get over its hysteria hsyteresis.)

[feanelwa.livejournal.com]

Gosh. Yes, I was assuming the liquid helium would be staying put, otherwise you may both die a very squeaky death of suffocation.

[venta.livejournal.com]

As I understand it, you try to keep the helium in because it is expensive. Patient breathing is less important :)

[exspelunca.livejournal.com]

And the world supply is dwindling rapidly

[venta.livejournal.com]

Interesting point!

I'm always amazed at the wealth of experience and information people can produce on here, thanks :)