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Maybe. MRI is not the preferred brain imaging modality in emergency situations, X-ray computed tomography is. Consider patients who are unconscious (or awake b
by mohn 7y ago
Maybe. MRI is not the preferred brain imaging modality in emergency situations, X-ray computed tomography is.
Consider patients who are unconscious (or awake but unreliable) due to head trauma, stroke, etc. You can't do a proper MR safety screening interview to find out if they have ferrous metal or other conductive objects in their head. The magnetic field can potentially torque an old aneurysm clip or piece of shrapnel, and the radio frequency excitation field can cause heating and burns if there are antenna-like conductors present.
MRI is slow and the images are easy to ruin if the subject moves around too much during the long acquisition time, so bouncing around in the back of an ambulance isn't the ideal setting. A 3D volume with whole head coverage and suitably fine spatial resolution can take several minutes to acquire, versus just a few seconds for X-ray CT. The MRI signal to noise ratio is also proportional to field strength, so low field systems like this are at a disadvantage for image quality. On the plus side, low field does mean less risk of moving ferrous material inside the subject.
- 01100011 7y ago> You can't do a proper MR safety screening interview Are we really not capable of detecting such dangers externally without patient input? It seems like detecting even small pieces of metal would be relatively trivial.
- askvictor 7y agoPresumably with an X-ray/CT scan.
- numpad0 7y agoCan’t you apply a minuscule power and watch out for overcurrent?
- ska 7y agoNo, the main field is effectively permanent.
- numpad0 7y agoI mean, some sort of non-super-conducting MRI analogue device that the patient will have to go through.
- ska 7y agoYou 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 agoSome 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 agoExactly! 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 agoWell, 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.
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- cma 7y agohttps://www.aan.com/PressRoom/Home/PressRelease/849 https://www.aan.com/PressRoom/Home/PressRelease/849 > According to the guideline, diffusion MRI should be considered more useful than a CT scan for diagnosing acute ischemic stroke within 12 hours of a person’s first stroke symptom. In one large study, among others, that was reviewed for the guideline, stroke was accurately detected 83 percent of the time by MRI versus 26 percent of the time by CT. Main thing they need to know is stroke vs aneurism and accuracy is really important.
- Amarok 7y agoIt has applications in emergencies[1].Speaking for the UK, every stroke center will want one. Dirt cheap as well. [1]https://news.ycombinator.com/item?id=22340458 https://news.ycombinator.com/item?id=22340458