Quenching your thirst for MRI science
This is a mini follow up to my Medical Imaging 101 series. MRI will be part 3. Consider this as a preview. Jean Liss shared an interesting video of an NMR magnet being quenched. http://goo.gl/cu1Ia
So what is quenching? What is the difference between an NMR magnet and an MRI magnet? Why are you showing me a picture of a chimney?
Superconducting: First let’s talk about superconducting. All magnets 1.4 Tesla and above are superconducting. Superconducting magnet are made of superconducting wires, typically niobium-titanium. The coils have no resistance when operated near absolute zero, 0 K. Liquid helium is the most common means of reaching and maintaining this temperature. A second coolant (cryogen), liquid nitrogen, is used to reduce the boil off of the liquid helium. Most modern units have a closed circuit refrigeration system so that you don’t have to top off the liquid nitrogen. Wiki: http://goo.gl/iufzR
NMR vs. MRI: What’s the difference? The video shows an NMR magnet being quenched. An NMR magnetic is used for spectroscopy, which doesn’t require gradient coils to create magnetic field gradients. MRI magnets use gradient coils to “encode” the position of each signal.
Quenching: Quenching is when the liquid helium or nitrogen boils off rapidly and loss of superconductivity of the current carrying coil (magnet). The superconductive coil becomes resistive and heats up, eventually boiling the liquid helium. For large magnets, enough helium gas can be released to displace all of the air, causing asphyxiation. Most MRI magnets are in small enclosed rooms for shielding purposes. Also, the force of the release of gas can be strong enough to blow out walls. So most MRI installations have a quench stack, a pipe that releases the helium outside of the room/building. So there you go, that’s what a quench stack is (pictured below, the third image is the hatch that was used to get the magnet into the room).
If you missed pt 1 and pt 2, they are here http://goo.gl/LTWUf and here http://goo.gl/IHaFw
#CHMedicalImagingSeries
#ScienceSunday #ScienceEveryday curated by Allison Sekuler Rajini Rao Robby Bowles and me. This week we are pleased to have guest curator Rich Pollett
We think of quenching as a four letter word in our labs 😉
Allison Sekuler we have a big plastic cover around the emergency quench button. Anyone who hits that accidentally is in big trouble with the boss.
Thanks Peter Lindelauf glad it was interesting.
We also have a big sign outside the MR room that says, “The magnet is always on.” Don’t want a rogue cleaning person to end up with a floor polisher lodged in the core….
Our research pre-clinical magnet is only accessible by us. However, I’m guessing there was a small accident with the clinical magnets. I heard that the cleaning staff had to go through MRI safety training.
We haven’t had any issues at our place, but we’ve seen too many examples of accidents at other places, so we take safety really seriously ;).
Peter Lindelauf our resident metal head Mahesh Sreekandath will be sad.
Like fotos
I’m not sure what you mean, Adina Cojoc.