Why do MRI machines cost so much to shut off?
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So basically the magnetic field from the MRI comes from a huge current in the superconducting wires inside a liquid helium bath. The superconducting wires are special in that below a certain temperature, they can flow the current without resistance. Normally, because the current is so large, you want to slowly put it in or take it out, because if you do it too fast, it’s too “turbulent” for the current to flow without resistance. This heats up the wires and causes a runaway effect, which will boil off the liquid helium. In an emergency, you can’t do it slowly, so a lot of the liquid helium is blown off. For regular maintenance, you can take the current out slowly and the liquid helium is not wasted.
Normally, you can collect the helium flowing out and recycle it, but in an emergency, a lot of liquid is turned into gas and takes up a lot of room, so the pumps can’t collect all of it and most of the gas is relieved to atmosphere.
By the way, just to give an idea of the cost of helium. I work in lab settings not hospital so maybe the prices are slightly off. But 100L liquid helium costs about $1500 plus shipping and handling. Typical MRI machines holds 1700L liquid helium. So each emergency quench will cost $25K in just liquid helium, plus shipping and machine maintenance.
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