Absolutely not always. Yes, there are MRI with permanent magnets, but these are huge and only reach up to 0.4 Tesla. Electromagnets are the standard today:
No, you were right. MRI machines that can be turned on and off are of two varieties, the regular electromagnet, and the superconducting one. The regular electromagnet versions are obsolete, they take up to an hour of being turned on before you can get accurate measurements from them. Almost all MRI machines in operation today are of the superconducting type.
Superconducting magnets take hours to turn on. They need to get a lot of electricity running through them. It needs to be kept at a superconducting temperature, and charging it heats it up. They also take quite a while to turn off, though faster than turning on. Their fast emergency shutdown involves releasing their liquid helium coolant. If you want a video of this, search “MRI quench”.
These MRIs are only turned off for maintenance. MRI machine rooms are highly restricted, anyone entering must be screened for potentially dangerous objects. For more info, search for “are MRI machines always on”.
This is not how it works, though. As soon as the patient starts getting inside the machine - carnage.
The magnet is always active.
Edit: I’ve been schooled.
No, coins aren’t ferromagnetic.
Sure. But then why did the dude in the comic die, then? Exploding coins?
You have a better explanation?
I thought I did.
Absolutely not always. Yes, there are MRI with permanent magnets, but these are huge and only reach up to 0.4 Tesla. Electromagnets are the standard today:
“Helium cooled superconducting magnets are the most common type found in MRI scanners today.” - https://en.m.wikipedia.org/wiki/Physics_of_magnetic_resonance_imaging
Thank you. I’ve been schooled and I stand corrected.
No, you were right. MRI machines that can be turned on and off are of two varieties, the regular electromagnet, and the superconducting one. The regular electromagnet versions are obsolete, they take up to an hour of being turned on before you can get accurate measurements from them. Almost all MRI machines in operation today are of the superconducting type.
Superconducting magnets take hours to turn on. They need to get a lot of electricity running through them. It needs to be kept at a superconducting temperature, and charging it heats it up. They also take quite a while to turn off, though faster than turning on. Their fast emergency shutdown involves releasing their liquid helium coolant. If you want a video of this, search “MRI quench”.
These MRIs are only turned off for maintenance. MRI machine rooms are highly restricted, anyone entering must be screened for potentially dangerous objects. For more info, search for “are MRI machines always on”.