"During a quench, which is not common, a large amount of helium evaporates and is vented outside the building through a venting system," the recall explains. "If an unknown blockage is present in the venting system and the pressure exceeds design limits, the structural integrity of the system could be compromised."
This is a risk of any mri machine that uses helium to cool a magnet. Why are only these machines being recalled when if you block the exhaust of any mri scanner it will blow up?
This is just speculation, but maybe there is a secondary rupture disk that vents the helium inside the room when the primary path (the exhaust to the outside) is blocked. And maybe that secondary rupture disk is too strong, so another random part of the helium containment fails, blowing up the machine and possibly injuring the patient. But please note again that this is pure speculation.
Why not add a pressure relief valve on the quench path with a very loud whistle? That should be enough to take care of such rare and compounded failures.
What does recall means in this context? De-energizing the superconductor and shipping it back? Seems like a waste and a planning nightmare.
A bursting disc is commonly used -- the diameter of the quench pipe is typically around 20 - 30 cm. The gas flow rates are insane; a PRV would fail and likely still not reduce the pressure inside quickly enough.
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.
I do not work with MRIs, but I work next to the guys who run the NMRs (which is the ~same technology). It is my understanding that all of these super cooled magnets are designed for the eventuality of an emergency quench. Which means the machine has a direct path to evacuate the gas, and it should be piped into the building's HVAC so that if a quench does happen, the people in the area do not suffocate because of lack of oxygen.
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.
The problem is you dont know what you are talking about and dont even understand the questions people are asking.
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.
> Every MRI machine quenches and vents. The question is what is different, in detail, that heightens the risk with this machine.
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.
