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MRI-compatible and visible retro-reflective markers

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  • #1

    MRI-compatible and visible retro-reflective markers

    Hi,

    for my research I will perform a motion capture and I will make MRI scans of my subjects. I would prefer to leave the spherical, retro-reflective markers that I will use for my motion capture on the subject while making the MRI scan. It is therefore essential that these markers are MRI-compatible and visible on the scans. We don't have those markers and I am not aware of their existence. A search on the internet did not lead to any results. Do you have any suggestions? Does anyone know for example of markers that can be filled by contrast agent? Any tips would be much appreciated! Thanks!

    Bart
    Tags: motion capture, mri, retro-reflective
  • #2
    Re: MRI-compatible and visible retro-reflective markers

    Hi Bart,
    I tried this a few years ago with a bit of success. I encased an old marker in a small plastic cup ( marginally bigger than the marker), where the base of the marker effectively was the lid. I filled the cup with Copper II Sulfate solution, and glued the old marker on to seal it. I drew on the subject around where the marker base was at the 3DGA, and replaced them with my copper II sulfate solution encased marker for use in the MRI scanner. The copper II sulfate shows up in the scan, leaving a black sphere where the marker is. I had a bit of an image shift, but Frances Sheehan used copper II sulfate doped gelatin (ref below) which might work better.

    Chris


    Sheehan, F. T., Zajac, F. E., & Drace, J. E. (1997). Using cine phase contrast magnetic resonance imaging to non-invasively study< i> in vivo</i> knee dynamics. Journal of biomechanics, 31(1), 21-26.

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    • #3
      Re: MRI-compatible and visible retro-reflective markers

      Hi Bart,

      There are some markers made by Beekley that could be useful for you: http://www.beekley.com/MRI/PinPoint_SFV.asp These should be compatible with standard motion capture markers and visible in MRI images.

      Joe

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      • #4
        Re: MRI-compatible and visible retro-reflective markers

        Hi Bart,

        A relatively cheap and easy way to do it is buy paintballs and then cover them in reflective tape and glue to the base of your choice (rubber works well)

        Alasdair

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        • #5
          Re: MRI-compatible and visible retro-reflective markers

          Hello Bart,

          Please I would like to know if you published any papers based on your MRI-visible and retro reflective markers. I have a similar project but have not quite seen any papers that carry this out. Does anyone know of any papers?

          Your help is greatly appreciated,
          Kind Regards

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          • #6
            Re: MRI-compatible and visible retro-reflective markers

            Hi,
            We ended up working around the issue of retro reflective MRI-compatible and MRI-visible markers. We have tried using paintball bullets and sprayed them with retro reflective spray paint. It didn't work great though. The sprayed paintballs weren't as visible to our mocap system as the official markers, but most importantly they didn't show up well on our MRI scans. This problem can probably be resolved by using fish oil capsules. Fish oil shows up very well on MRI so if you can find round capsules you could try spray painting those with retro reflective paint.

            Hope this helps.

            Bart

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            • #7
              Re: MRI-compatible and visible retro-reflective markers

              Hi Ibukunoluwa,

              If you’re looking for an alternative solution, The MotionMonitor software provides three methods for registering a CT or MRI scan with motion capture data. Some of these would alleviate the requirement to have the reflective markers attached during the scan. For example, you could use anatomical landmarks (identified in both the scan and biomechanical model) to register the scan tothe motion capture data. The result is detailed motion analysis based on the subject-specific bone geometry.

              Additional information is available here: https://www.innsport.com/applications/landmark-tracking.aspx

              Good luck with your research!

              Meredith Evans

              Innovative Sports Training, Inc.
              mevans@TheMotionMonitor.com
              www.TheMotionMonitor.com

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              • #8
                Re: MRI-compatible and visible retro-reflective markers

                Motion Capture passive markers being made of inert material should not pose any interference in MRI signals, provided marker base and marker posts too are not metallic. You will have to register motion capture data with MRI data though by some means, for example using anatomical landmarks as mentioned by Meredith.

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                • #9
                  Re: MRI-compatible and visible retro-reflective markers

                  Hello:

                  Qualisys manufacturers a complete 3D - MRI Motion Capture system. Such systems require lightweight, non MRI interfering spheres. These can be found at our website: http://www.qualisys.com/accessories/...weight-marker/

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