Right, but that's true of all MRI's - so what's different in this one?
A blocked quench pipe and a stainless steel (typically A4 stainless) cryostat becomes a bomb: cryogens expand in volume by about a factor of ~700 when boiling and so the volume they occupy at 1 bar and 300 K is, well, far far larger than the volume of the room the scanner is in.
This is the sort of thing that is a (remote) risk to life. I've only ever seen one (preclinical, not-for-human-use) magnet unexpectedly quench; copying and pasting a paragraph from my PhD thesis:
*The overpressure created by the rapid boiling of the large volume of liquid helium surrounding the superconducting magnet was sufficient to burst the bursting disc (as designed), which allowed the venting of helium gas from the inner cryostat to the emergency quench pipe (the bursting disc was temporarily replaced by clingfilm in this photograph). Additionally, it was also sufficient to rip and blow off the quench pipe, break two windows, damage the floor, and relocate several light items within the magnet room (which, presumably, was not as designed)*Every MRI machine quenches and vents. The question is what is different, in detail, that heightens the risk with this machine.
your response is like saying "the engine wont work" as a complete explanation for why a type of car has more automotive problems than another. Then, when a mechanic is curious about the nature of the failure, you call them stupid, saying "I already told you, i said it doesnt work!"
I certainly hope you are not in charge of solving problems in any professional capacity.
The design can't safely accommodate the level of energy that ends up in the machine if its clogged.
In the spirit of analogies, it's like asking why a 10 oz glass overflows with 200 degree water and a 10 oz glass doesn't overflow with 100 degree water. It exceeded it's capacity.
There's nothing more complicated to it, you could call in an MRI technician, get the PDF manual, talk to several doctors, disassemble it and put it back together, and learn no more than that.
You got extraordinarily rude and personal, I hope you don't do that often on HN, that was an outlier in my 13 years here. I hope all is well and it's an exception.
What does recall means in this context? De-energizing the superconductor and shipping it back? Seems like a waste and a planning nightmare.
A surprising amount of maintenance can occur while the magnets are cold and energized. My armchair-uniformed-guess is that they can replace the not-always-working relief path without venting.
Remember, cryostats are like Russian dolls suspended on torsion wire. You want the mass of the metal inside to be as low as possible because it forms cold bridges to the outside world and increases the boil-off rate. Quenches should not happen once the magnet leaves the factory, but until that point it's not uncommon for a machine to have several "training" quenches as the (typically NbSn or NbTi) superconducting wire effectively anneals in place. A fixable giant hole in the top (with a graphite, insulating series of bursting discs) is the approach usually taken.