• brendansimms@lemmy.world
      link
      fedilink
      English
      arrow-up
      0
      ·
      1 天前

      Just going through comments spreading MRI information (source: I work with MRI scanners). Nothing is spinning inside the MRI machine. CT scanners have an internal spinning component, but MRIs do not.

      • zr0@lemmy.dbzer0.com
        link
        fedilink
        English
        arrow-up
        0
        ·
        1 天前

        Thank you, I actually did not know that. While we are at it: what is causing the sounds? And how often do those machines have to be calibrated, as I believe the RF receivers (?) have to be super sensitive and accurate.

        • brendansimms@lemmy.world
          link
          fedilink
          English
          arrow-up
          0
          ·
          21 小时前

          The sound is caused by ‘gradient coils’ that are being switched on and off at kHz frequency, which is in the audible range for humans. The sound is caused by those coils vibrating due to the interaction of the magnetic field with the electric current in the coils: they’re non magnetic but they still feel the ‘Lorentz force’. As far as calibration, there is a pre-scan step (which is one reason why MRIs can take awhile) used to optimize the RF settings to each patient. Patients come in many shapes and sizes so the settings have to be tuned to get a good image every time. I’m actually not sure of how often they need to be serviced, but it seems like the manufacturers are here checking on the machines pretty often!

    • Kazumara@discuss.tchncs.de
      link
      fedilink
      English
      arrow-up
      0
      ·
      2 天前

      The detector spins around the patient, but does the magnetic field spin too? I though not, but I’m not that certain.

      • Ledivin@lemmy.world
        link
        fedilink
        English
        arrow-up
        0
        ·
        edit-2
        2 天前

        Nope, the detector is separate from the magnet - the magnet encircles the patient completely, and doesn’t move. I’m sure the magnetic field is affected slightly by the rotating machinery, but that should be consistent and would be accounted for in the imaging algorithms.

      • zr0@lemmy.dbzer0.com
        link
        fedilink
        English
        arrow-up
        0
        ·
        2 天前

        I doubt it, obviously depending on the applied force.

        Skin is rather tough to rip with a blunt tool so yeah, maybe the head was disconnected from the spine immediately, making him look like a giraffe spinning at 12 RPM round and round.