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Medical MRI question

  1. Jul 17, 2008 #1

    lisab

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    About a year and a half ago, I had an MRI. During the scan something very strange kept happening.

    The procedure was actually a series of many scans - it took over an hour to get them all done. Before each one, the tech would go through a procedure he called tuning. The machine would hum at three different tones during this tuning. The third hum was where the strange thing would happen.

    I was on my back with my hands crossed across my belly. As soon as the third hum would start, my arms and hands would feel electric shock and fly apart. No matter how hard I tried to relax and keep my hands clasped, I couldn't. It wasn't painful, but I could not control my muscles at all. It would last maybe a second.

    The tech said it was the startle reflex. I can't rule it out, but since I knew it was coming each time I don't think that's what it was. I mean, in an MRI there are lots of different, unexpected sounds, and I didn't startle at any of those. Just the third one of the tuning process - every time!

    Later, when I saw the neurologist, he didn't have an explanation. He just sort of brushed it off.

    Anyone know what was happening?
     
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  3. Jul 17, 2008 #2

    Astronuc

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    Maybe Ivan Seeking can offer a comment, but it would be difficult without knowing the frequencies used. MRI use strongly local magnetic fields to excite magnetic resonances of protons (hydrogen) and selected nuclei in the tissue, and perhaps that induced some mild electrical currents in the body, or the magnetic field had some effect on the electrical impulse of the heart or nerve systems.

    It is disconcerting that the technician and neurologist didn't seem to understand what was happening.

    See more details - http://www.cis.rit.edu/htbooks/mri/inside.htm

    http://www.hull.ac.uk/mri/lectures/gpl_page.html

    http://www.mritutor.org/mritutor/
     
    Last edited: Jul 19, 2008
  4. Jul 17, 2008 #3

    lisab

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    Two of those links mentioned that high dB/dt can cause peripheral nerve stimulation! That has to be it. And it makes sense that the higher dB/dt only occurred during the tuning - they were probably bracketing the frequencies that they were planning to use during the scan.

    Thanks Astro :smile: !

    But is this common? The people I have spoken to who have had MRIs didn't experience this.
     
    Last edited: Jul 17, 2008
  5. Jul 18, 2008 #4

    Tsu

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    It's not something that I've ever heard of, but I'll try to remember to ask one of our MR Techs. I'm going to stop off at work tomorrow to say hi and I'll see if one is working when I get there (it'll be later).
     
  6. Jul 18, 2008 #5

    Dale

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    If it was not a startle reflex then my guess would be peripheral nerve stimulation. Did you have sweaty palms at the time?

    Generally a good staff will tell you to not clasp your hands over your belly. They will tell you to lay your arms at your side or to keep your hands separated. If your hands are sweaty at all and you clasp your hands on your belly then your arms and shoulders form a rather large loop in which to induce currents.

    Peripheral nerve stimulation is not itself dangerous, although as you experienced it can be disturbing to the patient. It generally occurs only when the dB/dt is high in the anterior-posterior direction since this is normal to the largest loops you can form in the body. Also, some people are simply more sensitive to peripheral nerve stimulation.

    Although it is not something that is dangerous, all the manufacturers have to limit their system's so as to reduce peripheral nerve stimulation.

    Having said all of this, I am surprised that the adjustment procedure is what triggered it, usually the adjustment uses fairly low gradients.
     
  7. Jul 18, 2008 #6

    Tsu

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    Well, there ya go. An excellent answer from a REAL expert. :biggrin:
     
  8. Jul 19, 2008 #7

    Ivan Seeking

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    Not directly related, but I was wondering if you have ever heard of anything like this: We once had an MRI tech who had an MRI done on her own unit [a mobile]. Although she never made a sound during the entire study, and though she was awake, when the study was done, she claimed that she had been screaming to be let out.

    It was attributed to claustrophobia, but she claimed that she wasn't claustrophobic.
     
  9. Jul 19, 2008 #8

    Dale

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    I haven't heard of something like that. Could it be as simple as having the volume turned off for the intercom?
     
  10. Jul 19, 2008 #9

    Ivan Seeking

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    No, she could be seen through the window the entire time, and the intercom worked. The fact that she didn't accept the claustrophobia explanation made it all rather interesting.
     
  11. Jul 19, 2008 #10

    Tsu

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    Every time I go near our MR scanner I just want to walk North in the WORST WAY!!!11 :rofl:


    oh. sorry. ok. i'll stop now. :biggrin:
     
  12. Jan 10, 2009 #11
    Obviously I can't identify my company, but about 10 years ago a new type of exam (with hardware changes) came out that uses steep gradients and short Tr times. (back when the normal MRI sounds changed from "buzzing" to "humming"). We heard about the effect LISAB describes a lot. It was happening during this special exam, not tuning, but my point is that our educators (and literature) started suggesting right away that for ALL exams not to clasp hands, for the exact reasons mentioned by DALESPAM. All manufactures now have this technology and I would think give the same instructions. This is surprising.

    Maybe it's never been reported to the FDA as an injury, so it does not get special attention from the trainers?
     
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