3 ms·

Presumably with an X-ray/CT scan.

by askvictor 7y ago

numpad0 7y ago
Can’t you apply a minuscule power and watch out for overcurrent?
- ska 7y ago
  No, the main field is effectively permanent.
  - numpad0 7y ago
    I mean, some sort of non-super-conducting MRI analogue device that the patient will have to go through.
    - ska 7y ago
      You could find big things that way, but maybe not small things that were deep. I suspect it is hard to make something powerful enough to detect everything that might be an issue in say a 7T field, yet still safe.
- Amarok 7y ago
  Some devices are safe to scan at lower intensities and for less time, but it's the radiologist who check on that, so not my expertise.
mohn 7y ago
Exactly! Maybe my initial comment should have emphasized the relative significance of reasons for preferring X-ray CT over MRI in an emergency: 1) Speed. 2) Depiction of bone (less relevant if it's not a trauma case with suspected broken bones). ?) Risk to patient in case of internal metal. Some MRI suites are set up with airport style metal detectors to prevent people from accidentally bringing metal into the magnet room. I haven't heard of metal detectors being used to screen non-responsive patients, though. It's a reasonable question, but I think that even if some instantaneous metal detector with a false negative rate of 0 could be made, emergency docs would rather scan for five seconds to get a CT than five minutes to get an MRI that has coarser resolution, poor bone depiction, and a chance that the whole image is ruined if the patient moves.
01100011 7y ago
Well, obviously. What I'm saying is, why isn't there a sensitive enough metal detector which outputs a binary value of whether or not a dangerous level of metal is present? You need to check for two things I imagine: ferrous objects which could be pulled by the magnet, and conductive objects which would heat up when absorbing the MRI RF pulses. Both seem possible to do with a bedside device.

Presumably with an X-ray/CT scan.

numpad0 7y ago

Can’t you apply a minuscule power and watch out for overcurrent?

ska 7y ago
No, the main field is effectively permanent.
- numpad0 7y ago
  I mean, some sort of non-super-conducting MRI analogue device that the patient will have to go through.
  - ska 7y ago
    You could find big things that way, but maybe not small things that were deep. I suspect it is hard to make something powerful enough to detect everything that might be an issue in say a 7T field, yet still safe.
Amarok 7y ago
Some devices are safe to scan at lower intensities and for less time, but it's the radiologist who check on that, so not my expertise.

mohn 7y ago

Exactly! Maybe my initial comment should have emphasized the relative significance of reasons for preferring X-ray CT over MRI in an emergency: 1) Speed. 2) Depiction of bone (less relevant if it's not a trauma case with suspected broken bones). ?) Risk to patient in case of internal metal. Some MRI suites are set up with airport style metal detectors to prevent people from accidentally bringing metal into the magnet room. I haven't heard of metal detectors being used to screen non-responsive patients, though. It's a reasonable question, but I think that even if some instantaneous metal detector with a false negative rate of 0 could be made, emergency docs would rather scan for five seconds to get a CT than five minutes to get an MRI that has coarser resolution, poor bone depiction, and a chance that the whole image is ruined if the patient moves.

01100011 7y ago

Well, obviously. What I'm saying is, why isn't there a sensitive enough metal detector which outputs a binary value of whether or not a dangerous level of metal is present? You need to check for two things I imagine: ferrous objects which could be pulled by the magnet, and conductive objects which would heat up when absorbing the MRI RF pulses. Both seem possible to do with a bedside device.