A quench occurs when the superconducting wire losses its ability to super conduct. Freund explains, "This can only happen when the temperature around a part of the wire is raised above the temperature required. The wire goes to a 'normal' state which creates heat in the system causing a rapid boil-off of liquid helium and a loss of the magnetic field."

Because magnets can lose most of their reservoir of helium during a quench, the expense to repair this problem is costly. The downtime to repair a quench depends on how quickly a service expert can respond, but any downtime for an MRI unit means lost revenue.


Helium boil-off occurs continually inside an MRI magnet reservoir. Newer machines require less top offs, but liquid helium fills are a regular part of MRI service. Liquid nitrogen, which is less expensive than liquid helium, is used to cool a magnet during a quench.

Oxford Instruments makes the required checks of the system prior to refilling and re-energizing. Improper filling, failure of the fill line, ramping power supply problems and ice removal are all reasons magnets can quench. It is important that anyone performing any of these operations be fully trained to do so.

Highly trained technicians use specialized equipment: non-magnetic tools, helium siphons, gas flow regulators, helium leak detection equipment, turbo-molecular vacuum pumps, rotary van pumps, mass spectrometer leak detectors and oxygen monitors to perform repair services. It is preferable for service to be rendered by a technician who has been extensively trained from an OEM or a helium supplier.

Freund warns to check quench pipes regularly for water accumulation from rain or other sources. He tells of one of the most challenging situations he has encountered which involved deicing. "Most recently, our team needed to deice a magnet system in which water entered the magnet via the quench pipe. This type of ice (caused by water) is incredibly difficult to remove because of the low temperature inside the magnet. Magnets that have too much ice often need to be warmed up to remove the ice. Our team calls this a 'Thermal Cycle.' It is very time consuming and very expensive. We were able to clear enough ice on the system after days of hard work in a mobile environment. In the end, we were able to get the customer back on track."

"From a downtime and cost perspective, a cool-down process for an MRI can take 7-10 days and exceed $30,000. The process requires precise actions," described by Freund. "First, the system needs to have the vacuum established and leak checked. Even a system that has a vacuum needs to be pumped down prior to starting the cooling process. The magnet coil needs to be 'pre-cooled' with liquid nitrogen for some time and then have the nitrogen removed in its entirety prior to filling with helium."

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