Quench | MR system

Quench- MRI
MR system- Quench

Starting the Magnet 

When a magnet is started the first time, it is done in a particular way or sequence. First, the superconducting coil is cooled to -269 degrees Celsius by helium and liquid nitrogen. Then the magnet is energized by delivering current from the external power source to the superconducting coil. This process is called ramping. Once the desired level of current is achieved, the power supply is cut off. The current continuous to circulate through the coil as long as the temperature is maintained below -269 degrees Celsius. The current and the magnetic field produced remain constant and subject only to minor changes. 

Quench (MRI)

Quench is discharge or loss of magnetic field of the superconducting magnet. This occurs because of increased resistance in the superconducting coil, which results in heat formation. This heat in turn causes cryogens to evaporate. This sets in a vicious cycle, which ultimately results in increased temperature, increased resistance, evaporation of all cryogens, and complete loss of magnetic field, Triggering factor for the resistance could be minor the motion of wire in the coil or flux jumping, which results in heat production. Rarely quench can be deliberately performed to save patients' life. This is done in situations where the patient accidentally gets trapped in the magnet by objects such as an oxygen cylinder or wheelchair. All MR systems should have a vent to allow the helium to escape outside in case a quench occurs. Helium released inside the scan room can replace the oxygen completely and can cause asphyxia. It also produces increased pressure in the scan room, which may prevent the opening of the door. Every scan room should have an oxygen monitor that will alarm if oxygen level falls below a critical level. To restart the magnet after the quench, cryogens are filled and wires are cooled to -269 degrees Celsius. Then the ramping is done till a desirable level of a magnetic field is achieved.

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