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Around 1 p.m. on Dec. 7, 2006, an MRI magnet exploded at Atlanta Diagnostic Center in Kennesaw, Ga. According to media reports, one of the workers moving the machine at the time suffered an injured arm, and the other worker had shrapnel in the back of his head. The blast also exacted a toll on the facility itself, leaving a 10-foot by 10-foot hole in a nearby wall.
About a month later, in January 2007, an MRI magnet at a facility in Birmingham, Ala., blew up in the middle of the night. While no one was injured, the explosion decimated the building's MRI suite and damaged the facility's exterior walls and roof.
Another MRI magnet explosion, which occurred in 2003 at the Peninsula Regional Medical Center in Salisbury, Md., was caught on tape by a local television station (video of the incident is available at www.youtube.com/watch?v=1R7KsfosV-o). A local news outlet reported that the magnet--in the process of being replaced at the time--was being vented when it burst.
At least five MRI magnet explosions have occurred in the U.S. within the last 10 years, and there may be others that have gone unreported, MRI safety experts say. Officially, no reasons have been given for such incidents, but there are links that would indicate a common cause. And like many other accidents, MRI magnet explosions can often be prevented by taking precautions.
Not quite a quench
An MRI magnet explosion is not quite the same as a magnet quench, and it's important to differentiate between the two, says Robert Junk, AIA, AHRA, founder and principal in charge of medical design with MRI-Planning in Kansas City, Mo.
Nearly all clinical MRI magnets have a cryogen vent, or quench pipe, which acts to conduct escaping cryogens to a safe discharge point, such as a rooftop.
A quench occurs when cryogens are suddenly released or vented from the unit's cryostat. This happens when the cryogens convert from a liquid to a gaseous state, he says.
A quench can be set off manually, by a technologist, when there is a need to rapidly reduce the magnetic field of the MRI unit, Junk says. This is only done in emergency situations, such as when a person is pinned to the magnet by a large metal object that cannot be removed by hand. A quench can also be caused by outside events that destabilize the magnet, including extended periods of power loss, extreme vibrations such as an earthquake, or improper maintenance or operation of the MRI, usually associated with servicing the cryogens. A handful of MRI units also spontaneously quench every year for no apparent reason, Junk notes.
A magnet explosion occurs when the release of gas is interrupted or blocked, causing pressure to build up and rupture the cryostat vessel or the quench pipe with explosive force.
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