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I've had more than a handful of MRIs and that's never happened to me. Unless the injected contrast agent can induce reactions, my guess'd be psychological. Were you stressed? Nervous?

Edit: Quick Googling brought up some explanations, this abstract mentions measurements of nerve stimulation and muscle-twitching, and this call for participants in a clinical trial claims that nerve stimulation can be experienced as muscle twitching during MR scans:

During the MRI scan, patients may experience peripheral nerve stimulation, usually experienced as a muscle twitch. It is caused by rapid switching of magnetic fields and is not serious.

So it looks like that's a likely explanation for now.

That's really interesting. I've only had one MRI (lying down) and didn't experience muscle twitching then.

Claustrophobia, yes; twitching, no. I believe there are a lot of stand-up MRIs around now.

What hthth said. It's nothing serious, though you really shouldn't move in an MRI. That's why sometimes we give a relaxant to some patients. I've never seen one given but I've been to some MRI's because they need it to aspirate tumour in the chest cavity and we needed some clear imaging.

Didn't feel nervous (I actually dozed off for a moment).

My back was a mess, and I was very uncomfortable, and reasonably well drugged (hence the dozing off).

It felt VERY much like electro-stimulation of muscles, including the mild feeling of getting an electric shock. I'm fairly sure it wasn't in my head.

A friend who's a doctor theorized that aluminum in deodorant might've done it.

Likely it'll be one of those mysteries, until the aliens take me back and remove that damned implant.

The last one I had they strapped me down (no, really, real leather straps 'n shi.. stuff) so even if I wanted to twitch, I couldn't. ;)

Technically any ferris metal (iron) will react to a magnetic field, so whilst trace amounts of iron probably wouldn't be affected, we're still dealing with extremly potent electro-magnetic fields.

It could well be be a form of random 'noise' generated in the nervous system due to the magnetic waves interacting with existing nervous impulses (which are, essentially, an electrical signal).

> A friend who's a doctor theorized that aluminum in deodorant might've done it.

Unless it has a ferris element (i.e. an alloy) aluminium (or aloominum for you Americian types) typically doesn't react to magnetic fields unless there is a lot of energy involved.

An MRI might well have the power to do 'odd' things to aluminium, however the trace amounts used in deodorants is extremely small. I can't imagine a few parts-per-thousand is enough to move several pounds of limbs. ;)

My father just had an MRI yesterday, I'll ask him if he experienced anything similar.

Likely it'll be one of those mysteries, until the aliens take me back and remove that damned implant.

You noticed my edit above, right? Regarding nerve stimulation?

Thanks hthth! That sounds like the reason.

Glad to know this has nothing to do with superheroes or aliens...

I posted this to usenet group sci.med.radiology and sci.physics.electromag recently.

I recently had a head/neck MRI for chronic pain on the left side of my head, neck and back, ringing ears and dizziness. The scan went down to C1-C2. The MRI was taken in supine position. Towards the end of the scanning process I began to feel twitching in the front of my throat in synchrony with the banging of the scanner. This continued until the muscles on my left upper back joined in, twitching in time with the banging of the scanner. I assumed they were scanning the lower brain down to C1-C2 at this time
.
I asked the technician and his colleague about this and was told that synchronous twitching sometime happens (multiple events). His colleague said that she noticed the vibration on the monitor during this time. He seemed to be reluctant to speak (I assumed a long explanation would be required) so I didn't pursue it.

I heard nothing more about it. I assumed it may be of diagnostic value only because the area of twitching (contracting) muscles are where I have chronic pain. The ENT that ordered the scan did not know why and suggested I contact the radiologist. Unfortunately their policy is not to talk directly to patients. The ENT is reluctant to waste his time given that the scan was unremarkable with respect to dizziness.

I thought that the MRI would not interfere with the nerves causing firing potentials to be reached. Not meaning to beg the question but I do understand that hydrogen atoms are magnetically polarized then released and then release energy in the form of an RF wave captured by the face mask.

What I observed was that the muscles (Rhomboids in particular) fired (twitched, spasmed, went into tetany, no pain) in rhythm with the banging of the scanner (coincident events). The vibration of my muscles was observed by the technician (real macroscopic muscular event). It surprises me that RF waves would account for causing nerves to reach their firing threshold (needs further explanation). And it surprises me that it only affected an area of persistent pain (left side under scapula) and not both sides (another coincidence). Both sides of my brain were scanned. It ended with the last bang of the scanner but before I was drawn out of it (another coincidence).

If I am having persistent pain, the nerves stimulating those muscles are already hypersensitive and their firing threshold could be lower than usual. This specific area of twitching should then be diagnostically significant in demonstrating hypersensitivity and hence establish pain, inflammation and wasting muscles. The doctor having a further correlation with my previously stated symptoms, his observations and the objectively observed MRI experience why then are the results unremarkable.

The subjective experience of pain is not scientifically measurable and pain thresholds are subjectively reported and vary over time and across the population. Given the difficulty patients have in demonstrating the existence of pain from trauma why doesn't the radiologist use all of the available information. Given that I have no diagnosis except "you may have Meniere's Syndrome" which is not associated with pain (neurological component), I have no tattoos and never worked with metal materials. I would be interested in any comments. I am looking to understand.

Zachary