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Quench process (MRI specific)

 

Measures are put in place to ensure the safety of patients and staff in the event of a quench

 

+ Risks associated with magnet quench

  • A quench is an event that occurs when a superconducting magnet (such as those used in MRI) loses its superconductivity and undergoes a rapid increase in the resistivity of the magnet coil.1
    • The quench process once set off cannot be reversed and takes approximately two minutes2 
    • The quench generates heat that results in the rapid evaporation, or boil-off, of the magnet coolant (liquid helium)1

  • There are two situations in which a quench may occur:1
    • Spontaneously: due to some force or disruption to the magnet system (these events are rare) 
    • Intentionally: when the “Magnet Stop” button is depressed in response to an emergency situation

  • Evaporated helium created by a quench poses an immediate hazard to those in the vicinity of the magnet and the quench exhaust vent:
    • The coolant is extremely cold and can cause cold burn and frostbite within seconds for those that come into contact with it 
    • The rapidly released gas can enter the MRI scanning room (if there is a problem with the venting) and displace the oxygen, posing a risk for asphyxiation

  • A quench can also cause damage to the MRI equipment and disruption to the function of a department:
    • A quench can potentially damage the MRI magnet itself 
    • Regardless of the damage done, a quench will result in at least several days of system down-time, and recovery to operation is expensive

+ Intentional quench

  • Intentional quench is an emergency measure to be initiated in cases where no other alternative will suffice:1
    • Fire that cannot be controlled by the non-magnetic fire extinguisher 
    • An individual pinned against the magnet, trapped or in a potentially life-threatening situation by a non-removable ferrous object

  • In case of an intentional quench:
    • The MRI department is evacuated  
    • The exhaust fan is activated 
    • The door to the scan room is fixed open – a build-up of pressure in the scan room could make an inward opening door difficult to open3

  • Following the quench, the MRI department should remain evacuated until a suitably qualified person (e.g., a representative of the supplier) has inspected the system and confirmed it is safe.

+ Precautions for a quench emergency

  • MRTs should be aware of any and all local or provincial guidelines that relate to quench in their facility.
  • An accidental quench requires immediate evacuation of the vicinity.
    • Procedures are put in place to establish evacuation routes and responsibilities 
    • Evacuation procedures are reviewed by all staff on a regular basis

  • Safety measures are implemented to allow exit from the scan room in case of a quench emergency. These may include:
    • A reconfiguration of the door so it opens outwards 
    • Installation of sliding doors that can be opened in an emergency 
    • Installation of emergency escape/ventilation panels on the door or in a suitable wall 
    • Provision of emergency equipment to allow MRTs to break a window in the event of door malfunction

  • Police and fire response personnel are restricted from entering the MR scan room with their equipment until it can be confirmed that the magnetic field has been successfully dissipated.4

+ References

  1. Queens University. Centre for Neuroscience Studies. Queens’ MRI Facility Standard Operating Procedures: Emergency Shutdown and Quench Procedures. Available at: http://www.queensu.ca/neuroscience/MRI-facility/operation-procedures/shutdown.html. Accessed November 3, 2014.
  2. Louisiana State University Health Shreveport Radiology Department. MRI Quenching the magnet. Available at: http://www.sh.lsuhsc.edu/raddept/pdf/sec14/Rad%20Proc%2014.13.pdf. Accessed November 3, 2014.
  3. Medicines and Healthcare products Regulatory Agency (MHRA). Device Bulletin: Safety Guidelines for Magnetic Resonance Imaging Equipment in Clinical Use. Available at: http://www.mhra.gov.uk/home/groups/dts-iac/documents/publication/con2033065.pdf. Accessed November 3, 2014.
  4. Kanal E, Barkovich J, Bell C, et al. ACR Guidance Document on MR Safe Practices: 2013. J Magn Reson Imaging 2013;37:501-530.

Validation

October 9, 2014

 

 
Canadian Association of Medical Radiation Technologists
85 Albert St, Suite 1000, Ottawa, ON, K1P 6A4
phone: 613 234-0012 / 800 463-9729
fax: 613 234-1097
www.camrt.ca