MRI Quenching

I learned something new this week. Modern MRI scanners produce high-strength magnetic fields (typically 1.5T up to about 20T – scanners for use with humans max out at about 7T right now {those are very rare though, 1.5T and 3T are more common). To produce these fields the scanners need to have strong electric currents. In order to handle large currents, scanners use superconductors cooled with liquid helium. In cases of serious malfunction or emergency the MRI scanner can be quenched, which releases all of the liquid helium. The helium turns into a gaseous state rapidly and expands to fill the room. The quench will make a loud sound like a jet engine or a pop. If the room is small enough, all of the air can be pushed out as the helium expands and increases the pressure. Most MRI rooms have fail-safe systems that release the helium outside, which prevents the occupants from suffocating.MRI Quench

Image from here.

4 Replies to “MRI Quenching”

  1. Question about Quench… Is a quench a sudden loss of vacuum in the container the liquid helium is in? My limited understanding of MRI is the following…MRI magnets are usually a superconducting type of magnet. The magnet is made by a coil of wire wrapped around a cylinder/bore. When an electric current is passed through the coil there is a magnetic field generated. The wire in a superconductor is bathed in liquid helium (or other cryogens) at about -450C. I’ve heard that the liquid helium is kept under a vacuum state preventing it from becoming a gas.

  2. The helium is kept very cold to keep it in a liquid state (it is at close to normal atmospheric pressure, but it is in a tank surrounded by a vacuum as insultion.. as in a Thermos flask). Quench occurs if there is a fault in the superconductive path, causing a local rise in electrical resistance, therefore heating, and therefore boil off of gas and further loss of super conductivity, and therefore further boil off of helium etc etc

  3. Does anyone know how quickly after cooling will an MRI quench? I know it will depend on if the MRI is running or if it is ramped down, but any estimates?

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