An MRI quench occurs when the magnet coils suddenly lose their superconducting properties and become resistive, eliminating the magnetic field. This can happen accidentally due to a disruption or intentionally by pressing the emergency button. When the button is pressed, the helium rapidly escapes from the cryogen bath, requiring evacuation. A quench recovery requires time and special equipment to re-cool and re-energize the magnet. Safety precautions are important both before and during a quench.

1. Quench of MRI

2. What is Quench ?
Quenching is the process whereby there is a sudden loss of
absolute zero of temperature in the magnet coils, so that
they cease to be super conducting and become resistive,
thus eliminating the magnetic field. This results in helium
escaping from the cryogen bath extremely rapidly. It may
happen accidentally or can be manually instigated in the
case of an emergency.

3. Magnet coil component

4. What are causes of Quench ?
There are two situations in which a quench occurs :
● 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

5. What may let quench occur accidentally ?
● Further measures taken to minimize the loss of liquid helium are the
addition of a coldhead and compressor system, which functions
essentially like a high-tech refrigerator.
● The coldhead-compressor system, when it’s working properly, means
there is almost no loss of liquid. When the coldhead-compressor fails,
sometimes the magnet slowly loses liquid and sometimes it loses liquid
rapidly. If the air conditioning in the equipment room fails (or for some
systems, the water chiller) and the room heats up, the compressor will
shut itself off, and the liquid helium will start to boil off rapidly the
magnet can become unusable relatively quickly.
● The magnet can also warm up due to power failure or a broken
component in the magnet refrigeration system.

6. What happened when emergency button
pushed ?
● The coils of the magnet are encased in a thermos
bottle-like housing to minimize heat leaking into the
innermost part of the magnet. These thermal losses
which result in the liquid helium ‘boiling off’ into
helium gas, which is then lost to the atmosphere as it
exits through a small vent.
● 1000 liters (liquid helium) =700,000 liters (helium gas).
● So this huge amount of gas may break burst disc while
going to the vent and the burst disc is keeping the
pressure in the coil and it made of graphite .

8. When you should push emergency button ?
• A life-threatening accident (e.g. a person is trapped
between a heavy ferromagnetic object and the magnet)
• An uncontrollable fire in the Magnet Room which requires
the use of ferromagnetic fire-fighting equipment
Note: The decision to quench the magnet should be made
by an Authorised Person.

9. What are precautions before quench button
being pushed ?
● 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 open
Note: 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.

10. What are Precautions for a quench
accidentally ?
● 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.

11. Escape and Evacuation Routes

12. Quench Recovery
MRI magnets are designed to recover from a quench to be
re-energized again. But it’s expensive and slow to recover;
the service engineer will have to spend considerable time
to do the work and it requires special tools, power supplies,
and a supply of liquid helium. In some cases, if the magnet
has gone to near-room temperature, it’s necessary to bring
in special vacuum pumps and go through a time-
consuming re-cooling process. Because the tools and liquid
helium aren’t always immediately available, if your magnet
quenches, it’s usually several days before it can be used
again.

13. Steps of quench recovery
● Determine the status of your magnet
● Recommend a plan of action
● Disperse a qualified magnet engineer to your location
● Disperse all needed equipment to service the magnet
● Replace O’ rings and reseal your magnet
● Pump down to high vacuum specification
● Cool the LN2 and LHe temperature
● Re-energize and Re-cryoshim the magnet

14. MRI quench fill safety tips
Wear this things to protect you:
● Protective Goggles used to protect the eyes from injury due to flying cold liquids
and parts.
● Protective Gloves used to protect the hands from injury caused by contact with
extremely cold liquids or surfaces and for protection from injury caused by rough
edges.
● Protective Clothes used to protect the body from injury caused by contact with
extremely cold liquids or surfaces and for protection from wounds.
● Safety Shoes used to protect the feet from injury from falling of heavy objects. An
anti-slip sole protects from injury caused by slipping and falling on slippery floor
and steps. Only use safety shoes with non-ferromagnetic toe caps.
● Portable Oxygen Monitor and Alarm used to warn against low oxygen
concentrations in surrounding air