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Medicine

MRI Magnets Cause Nystagmus 120

Posted by Unknown Lamer
from the twirling-twirling-toward-vomit dept.
Hitting the main page for the first time, tibit writes "In an interesting twist on 'it's so old it's new again,' Johns Hopkins researchers led by Dale Roberts found what must have been causing much confusion for doctors the world over: strong external magnetic fields can stimulate the semicircular canals, causing vertigo and nystagmus (pendular eye motion). It's a textbook case of the Lorentz force in action: our angular rate gyros, the semicircular canals in the middle ear, filled with endolymph, have a ionic current flowing across. In a magnetic field, the current produces a force that pushes the lymph along the channel, causing stimulation of the cupula — a pressure sensor at the end of the channel. This is interpreted by the brain as rotation of the head in space, and causes a nystagmus that's supposed to stabilize the image on the retina. Of course, the subject is laying down and not spinning in space, and the mismatch between inertial measurements coming from the ear and the real situation causes vertigo."
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MRI Magnets Cause Nystagmus

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  • by grub (11606)

    We have MRIs at work, I get that Just-Stepped-Off-A-Roller-Coaster dizziness when moving through the field, the effect is well known.

    Old news or am I missing something?
    • Re:woozy (Score:4, Insightful)

      by nedlohs (1335013) on Tuesday September 27, 2011 @04:48PM (#37531648)

      Knowing it happens isn't the same as knowing the mechanism behind why it happens.

      • by grub (11606)
        One of the researchers here called it Vestibular [forget the word]. I googled it and there it was.
        • by hedwards (940851)

          That's probably vestigial. Which is basically just a way of saying that they don't know if it's useful any longer. People say the same thing about the ability to wiggle ones ears, even though it serves precisely the same purpose as it does in animals.

          • by siride (974284)

            No, he meant vestibular (having to do with the various balance systems in the head) and it's definitely *not* vestigial.

          • by sjames (1099)

            No, it probably isn't. We're pretty sure we still use our Vestibular system (our sense of balance).

          • ...No.
          • by grub (11606)
            Quote from the researcher I mentioned in email, emphasis mine.:

            Yes there is definitely a <b>vestibular</b> response that many people get when they move in and out of the magnet.

            I trust her PhD... :)

      • by cwebster (100824)

        I'd say the effect is known. What may be new is that the fluid is ionic and interacts with a magnetic field. You can induce the same effects in an airplane, where its pretty easy to apply accelerations to your body that your ears (vestibular system) will interpret one way and your eyes in another way. Vertigo.

        • by tibit (1762298)

          Fluid being ionic is one thing, but there are actually ionic currents, and that's what the dealbreaker. And they must flow perpendicular to the pipe holding the fluid (the semicircular canal). It's an interesting confluence of things.

    • I didn't realise chiropractors used MRI units...

    • by DeadCatX2 (950953)

      I think everyone knew that physically moving through the magnetic field can cause physiological responses. What surprised me is that even for a stationary subject, there's a physiological response.

      Unfortunately, the article is VERY light on details. It doesn't even say how strong the scanners were. Can they recognize this effect in a 1.5T? In a 3T? I would certainly believe as you get up to 7T that some strange shit can happen.

      • by iroll (717924)

        What's the difference between physically moving through a magnetic field and a stationary object experiencing a moving magnetic field?

        (spoiler alert: there isn't any)

        • by DeadCatX2 (950953)

          I won't argue with you on that point.

          However, the primary magnetic field in an MRI does not move. In fact, it must be as uniform as possible, and shims are used to make sure that the field homogenous.

          The gradients change the field, but by orders of magnitude less than the primary field.

          • TFA doesn't give real numbers, but it stated that the newer (more powerful) MRIs tended to cause more problems than "old" ones.

          • by iroll (717924)

            Ok, so the field is uniform in orientation and magnitude spacially, but not uniform in magnitude temporally. You're "sitting still in a uniform field" that's changing in magnitude... which is going to induce eddy currents in a conducting fluid, which you're full of =)

            And it had better be changing in magnitude, or else we wouldn't get Magnetic Resonance Imaging out of it!

            The physics of this is all very high school; it's the physiology that's interesting to me.

            • by cnettel (836611)

              ...And it had better be changing in magnitude, or else we wouldn't get Magnetic Resonance Imaging out of it!

              ...

              The resonance isn't caused by changing magnitude in the main field (B0), which is the strong field here. By imposing a static, homogenous magnetic field, however, the nuclear spin states separate slightly in energy. If you send a RF pulse with the right frequency, you can observe resonance back, caused by the excitation between the states. Matter rich in 1H nuclei (like water) will show more resonance, detected in the receiver coils.

        • as in- subject perception?

          imagine you have the ability to increase and decrease gravity localized to me by 1 percent.

          if I'm lying down, and you range gravity from .99 to 1.01 of normal, I may notice something weird.
          if I'm doing a straight bike riding on a bumpy road I may not.

          on a trampoline, it may well depend on how you time the changes, but I may never notice.

    • I've been working around MRI's for the last 20 years, yes you can get woozy, not so much at 1.5 Tesla definitely at 3 Tesla and at 7 Tesla people have been known to loose their lunch. It's nice they figured out the mechanics of why it happens, the magnetic field affects people differently.

      FYI during the scan coils change the magnetic field rapidly to produce the cross sectional image aka "slice" this rapid change of the magnetic field in the coils, X,Y and Z plane while in the main magnetic field is similar

  • Anyone who works around MRI magnets has known this for years. When I was a graduate student, you would always hear stories about people moving their hear around the end of the magnet (where the field gradient is highest) and making themselves dizzy.
    • by pz (113803)

      I did this just the other day! It's actually a bit scary because if you are just working with the magnets (and not a subject), then it only happens with high field systems. You know, the ones that can accelerate a forgotten pen or a paper clip into a lethal weapon. And it happens just when you're leaning your head over the entrance to the magnet, making an adjustment, and likely to be doing something stupid. It was scary the first time it happened to me, and it still gives me serious pause when I approa

      • Re:This is not new (Score:4, Interesting)

        by tibit (1762298) on Tuesday September 27, 2011 @09:03PM (#37534478)

        Do not close your eyes, and keep plenty of illumination (the more the better). This can at least inhibit the nystagmus to some extent. So at least you won't lose your visual acuity. The extra scary part, when talking about paperclips and such small things, is that inappropriate nystagmus (such as in a large magnetic field) causes you to lose visual sensitivity to high spatial frequencies, and paradoxically increases sensitivity to low spatial frequencies. You stop seeing small stuff, and you can remain unaware of it. The brain will, for a while, substitute made-up stuff to match your expectations. This is what gets fighter pilots killed: they get G-force induced nystagmus, lose acuity needed to read the instruments, and their brain is substituting expected (but incorrect) values for real instrument readings...

    • by PopeRatzo (965947) *

      Anyone who works around MRI magnets has known this for years.

      Chinese medicine has long emphasized the reaction of the otolithic structures that provide the brain with the ability to sense roll, pitch and yaw in regard to the position and movement of the head to magnetic fields. Why would we think that the structures of sense should only be affected by only very specific and arbitrary portions of the spectrum?

      We have somewhere between 9 and 21 different senses (a sense being defined as the physiological cap

      • by Cyberax (705495)

        On what magnetic fields? MRI fields are _tremendous_, you won't be able to sense anything with simple hand-held magnets, even with the rare-earth ones.

      • by tibit (1762298)

        The chinese medicine is bullshit in that regard. There are no natural magnetic fields anywhere on Earth that are big enough to cause this effect.

    • by tibit (1762298)

      The original article in Current Biology (abstract free, rest behind paywall) clearly says that gradients are irrelevant. It's a Lorentz force, for that you simply need a large static field. Moving your head probably exaggerates the effect because there's a mismatch between vestibular input and visual and proprioception inputs. What's important is that for the first time they had clearly shown that it's a Lorentz force, causing a pressure signal to be applied to the cupola in the semicircular canal. Nobody e

      • by ceoyoyo (59147)

        The Lorentz force is f=q[E + (v x B)]. That is, if you've only got a magnetic field you need some v in order to get some f. The charge has to be moving in relation to the field. In the paper they use a form of the equation with current instead of a moving charge, but it's the same thing.

        They DO test in a static field, and see an effect, which suggests that there is a continuous current in the semicircular canals (which seems weird). A changing field (due to head movement or gradients) would certainly in

        • by tibit (1762298)

          Yep, there is a constant current, and just ever so conveniently it flows across the channel (diametrally across the smallest cross-section).

  • by Anonymous Coward

    Radio Wave Propogation too.

    Outside of EMF and RF, scar tissue and acidosis is the verry location where most cancer forms. This would explain why Cell Phones and other phenomenons are LINKED to cancer but they don't cause cancer but simply impede the Immune System long enough that a culture of pathogen can increase it's generations to adapt and grow into the body while the Immune System is dysfunctional.

    • by YodasEvilTwin (2014446) on Tuesday September 27, 2011 @04:58PM (#37531818) Homepage
      Congratulations, you know absolutely nothing about cancer or biology in general.
      • by vlm (69642)

        Congratulations, you know absolutely nothing about cancer or biology in general.

        Don't overestimate the physics displayed either... there is a huge difference between slowly moving thru an intense static magnetic field and an electromagnetic wave.

        I suppose when anything technological is magic, all you have to guide yourself is fear...

    • by N0Man74 (1620447) on Tuesday September 27, 2011 @05:03PM (#37531872)

      Forget magnets....

      Fucking cancer, how does it work?

    • by poetmatt (793785)

      This is about as accurate in terms of "cell phone cancer" as comparing your ability to sense a volcano's heat from dipping your toe in the lava versus the ability to test the ambient air temperature being 1/3 of a degree higher or lower than your body temperature in a room without wind.

      One is painstakingly obvious, the other will basically never happen. That's how big of a different these MRI magnets are.

    • by TeknoHog (164938)
      You're unbelievable.
  • by ackthpt (218170) on Tuesday September 27, 2011 @04:55PM (#37531758) Homepage Journal

    The rapid eye movement, looking from side to side, peeking under things, etc. while out geocaching near guardrails.

  • by nikolag (467418)

    This is a classical example of how you just have to take the time to read the paper and think about it because the cited text and other sources that are not behind pay-wall are just not clear enough.

    I have had put my head in number of MR scanners, with field strengths of 0.3T, 0.5T, 1T, 1.5T, 2T, 3T, and 7T, with no nistagmus, but that simply does not mean anything in context of this paper.

    You should have in mind that the maximum magnetic field gradients, and their speed are regulated by law.
    Interesting que

    • by DeadCatX2 (950953)

      I agree with most of your post. I've been in a scanner a few times, and I knew a guy who has had probably in excess of 100 hours being scanned. I also know a lot of people that regularly go into the magnet room. The only issue anyone has ever had involved moving their head rapidly through the field.

      I disagree with fMRI point, though. An fMRI usually involves a control task (e.g. read these words but don't talk), and an experiment task (e.g. read these words and say them aloud). Then the images collecte

      • As long as you control for the vestibular response of your subjects -- or have enough to drown the effect out. Having vestibular issues isn't all that uncommon -- my daughter has been seeing an occupational therapist for just that.

    • by tibit (1762298)

      Try it with your eyes closed, in a darkened room :) Some people are better than others at suppressing nystagmus when there's something to look at.

      The effect does not care about gradients, just about a static field. Most people are blissfully unaware of having nystagmus, you'd have to train yourself to recognize it. Our visual system will lie to you when you have nystagmus and you'll feel like you don't have it.

    • by ceoyoyo (59147)

      Unfortunately reading the paper itself doesn't immediately make things much clearer. These guys should learn about the "Methods" section.

  • ...to explain the eye rolling when people read the bill for the MRI.

  • I have BPPV so I get dizzy pretty easily but after at least twenty MRIs I've never felt anything other than claustrophobia. I wonder if you have to go in head first to get the effect.

    • BPPV is frequently caused by solid matter (calcium crystals) in the semicircular canals coming loose, floating around, and moving the fluid in abnormal ways to cause stimulation and therefore vertigo. Wikipedia has a good article on the subject [wikipedia.org] and provides descriptions of two head-positioning techniques that you can do by yourself at home to help the solid matter settle back to where it will (at least temporarily) stop causing problems.

  • MRI subjects are often lying down, but I don't know what they would be laying down.
  • by History's Coming To (1059484) on Tuesday September 27, 2011 @06:13PM (#37532856) Journal
    A quick note to tibit, the submitter, to say nice summary. No hyperbole, no outrageous barely marginable links to another agenda, a suggestion, mechanism and evidence. I really enjoyed it, a bit of my brain went "Really? Oh? Like that? Oh that's quite clever, I see what happened there."

    You know, it actually makes me want to go and read the article. I think I will. Nice one. More weirdly interesting stuff like this please. Off-topic in many ways, sorry. If it makes up for it, I learned to look for nystagmus when working as a bartender. There's a fairly strong correlation between BAC and the degree of nystagmus in a drunk person as they follow an object with their eyes. You can use this to judge how drunk a person is fairly accurately. In the "controlled circumstances" of me asking off-duty colleagues and friends to follow a finger for ten seconds I could usually work out how much they'd had to drink to the nearest 10ml of alcohol (1/2 pint or a shot of whisky in the UK).
    • Erm, great summary. A link to some university rag, but none to the original article.
      • by tibit (1762298)

        Sorry about that. I meant to add the link to the article in Current Biology [cell.com], but somehow forgot about it before clicking "Submit".

        Alas, in my defense, the story was submitted and posted less than a week after the "embargo" was lifter by the publisher -- IIRC, it appeared online on Current Biology's website last Thursday at noon (maybe EST?). At least I didn't wait a year to submit :)

  • Years ago I participated in a paid research study as part of the control group. Part of the research was having an MRI done. After being in the MRI for a short period of time I had the oddest sense of vertigo, despite staying perfectly still. I asked the technician about this, and he brushed it off like it didn't happen, or I imagined it. I was sure he was just wrong, and went home and did my own research. I recall finding some people who had the same experience, but no real idea what the mechanism was

  • To clarify, giant magnets can temporarily induce nystagmus if you move around too quickly in their magnetic field. The nystagmus goes away when you leave. MRI machines cause nystagmus like wearing your winter coat in a sauna causes a fever.

    • by tibit (1762298)

      That's just too silly. They clearly showed that it's the static field. Gradients, both spatial and temporal, are not needed at all. The ionic current is already there, oriented just right. All you need is a correctly oriented static external field. It just so happens that we have semicircular canals sensitive in three almost-orthogonal axes, so the precise orientation doesn't matter all that much, unless you are looking at nystagmus in a single axis only. For all I know you could induce torsional nystagmus,

  • Hit them with the field, and they will fall over (and all their metal objects, teeth, fillings, etc, will get hot or go flying)

    • by tibit (1762298)

      Yeah, because high static magnetic fields cause things to get hot. And it's obviously easy to produce them on a large scale, here on Earth. Yee haw.

  • So, how long do you think its will take before the effect can be controlled with targeted, lower power magnetic fields to enhance virtual reality systems, from flight simulators to total immersive video games?

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