What is quenching?

Quenching is the rapid release of the liquid cryogens used to maintain the magnet of an MRI scanner in its superconducting state. Liquid cryogens are gases kept in their liquid state at very low temperatures. For MRI scanners, helium is typically used and allows the superconducting magnets to operate at a very low level of energy consumption. When the magnet quenches, the liquid helium evaporates and is vented out of the building, and the release is typically accompanied by a loud bang or hissing. The magnetic coils then change from being superconductive to resistive, and the magnetic field strength drops significantly (though not always completely to zero). Quenching may be spontaneous or intentional (i.e., by pressing the scanner’s STOP button); both causes are extremely rare. Spontaneous quenching may occur due to magnet malfunction, severe vibration, or insufficient or impure cryogens. Intentional quenching may be necessary if the magnet is resulting in injury to a patient or medical personnel, or in the event of a fire or other event that requires emergent access to the MRI scanner room.