How dangerous are magnetic items near an MRI magnet?

Fun, games and safety implications with a 4 tesla (T) MRI magnet that was about to be decommissioned. Note how magnetic objects let loose tend to oscillate along the magnet bore. That's because the peak magnetic field gradients are at either end (near the magnet face), causing peak acceleration as the object enters, followed by progressively damped changes of direction. See practiCalfMRI.blogspot.com for more information.

Category:

Science & Technology

Tags:

• mri
• safety
• magnets
• magnetism
• ferromagnetism
• tesla

[gorgeousdzastr]

I am so impressed with these idiots wasting valuable resources to stoke their curiosity at the average MRI machine costing over $1 million dollars.. nice use of specialty equipment.

You're fired!

[practiCalfMRI]

@gorgeousdzastr The magnet was a decade old and no longer used for research. Weighing four tons and requiring expensive rigging to remove/ship, and with a scrap value only in the tens of thousands (there's not much of a market for old 4 T magnets), it was better for us to convert it into a "mock scanner," for practice functional MRI sessions. So the specialty equipment is still in use, just not as a scanner.

[gorgeousdzastr]

@practiCalfMRI 4 tons, iron? What is the "magnet"? Is it coiled around ferrous material?

Got a procurement number? I may be interested in salvage. Of course depending on DOT requirements etc..

[practiCalfMRI]

@gorgeousdzastr The cryostat is steel on the outside, lots of Mylar and other gubbins on the inside. The wire is a superconductor, Nb-Ti alloy. Honestly, it's a lot of money to crane/move these behemoths! But if you *really* want one then it probably won't be difficult to find, provided you have the $50K-$100K for rigging/trucking! (And if you're on a university campus, for putting the grass and flowers back all nice... another $50K :-)

[practiCalfMRI]

@gorgeousdzastr PS we donated the old electronics and patient bed was donated to the manufacturer to support the three or four existing 4 T magnets still out there.

[askjerry]

Define QUENCHED - do you do something to it so that it will not function as a magnet anymore? I thought it was just a coil... a large coil... but just a coil. How do you prevent it from working... unless you burn it up?

[practiCalfMRI]

@askjerry A quench is violent; vibration can damage the superconducting wire, for example. And air ice can get into the magnet turret via cryopumping if a new burst disk isn't installed soon after the quench. In our case, though, we were done with the magnet. See my upcoming response to @gorgeousdzastr for why we went this route instead of a controlled run-down.

[JumleBumle]

Fucking magnets. How do they work?

[DivideByRy]

Freaking interns...

[TypesEvilAspieEyes]

I got piercings . A lot !! So I have to take them off when I get an MRI done or they get pulled out of my skin!!

[gorgeousdzastr]

@practiCalfMRI I could manage the rigging, but not 50K for flowers.

Thanks.. but no thanks. rofl I don't pay people to let me haul off their junk. :-O

cheers

[gorgeousdzastr]

@practiCalfMRI PS.. Your hired back.

rofl

[practiCalfMRI]

@askjerry In a controlled quench, using the magnet's built-in circuitry, all the electrical energy (tens of megajoules) is dumped as heat across diodes, causing all the liquid helium in the cryostat to expand and blow through a carbon "burst disk" located in a special duct atop the magnet. The circuit can be activated with an emergency button, it takes about 25-30 sec for the field to decay to near zero. More...