muppets

Turn the MRI off maybe ?

I was in one of those recently, and was wondering just how powerful those magnets really were. It's no wonder they don't let you in if you have any metal in your body, like surgical pins or bits of solder.

>> ^charliem:
Turn the MRI off maybe ?


Except that it's a magnet. You can't turn off magnets..

There was a kid killed in Philadelphia when someone left an oxygen cylinder in the room when they fired up the MRI. Very sad. They also ask if you work with metals in your job, because if you have a little chip of steel in your skin somewhere, or god forbid your eye it's big trouble.

>> ^JohnChrist:
>> ^charliem:
Turn the MRI off maybe ?

Except that it's a magnet. You can't turn off magnets..


Are you for real ?

Edit: Also, cant believe someone upvoted that. The collective IQ of VS just dropped 20 points.

This is from Wikipedia: http://en.wikipedia.org/wiki/Magnetic_Resonance_Imaging
The magnetic field and the associated risk of missile-effect accidents remains a permanent hazard — as superconductive MRI magnets retain their magnetic field, even in the event of a power outage.



Looks like it doesn't turn off even when turned off.

So that is why my teeth flew out. Those darn fillings!

Charliem: You can turn off *electro*magnets. And even then certain types will remain magnetic. You can't turn off a magnet.

>> ^Lucidium:
Charliem: You can turn off electro magnets. And even then certain types will remain magnetic. You can't turn off a magnet.


Simply not true.
The only electo-magnets that "retain" their fields after being switched off, are super-conductive rare-earth elements that have been super-cooled to very low kelvin temperatures.

When the material is bought back up past its super-conductive threshold, it loses its magnetic field.

Every electro magnet that can be switched off, loses its magnetic properties.

MRI's rarely use permanent magnets, as the resolution of a perm magnet is so low, and the materials required to produce a field strong enough for a clear picture, are immensely expensive, and heavy.

Theres a pretty decent chance this is an EM MRI, all they needed to do was let the thing warm up a bit after using it (generally by turning the cooling pumps off).

Well charliem, those MRIs are cooled with liquid helium which is quite expensive and it would take some time to warm up and cool down again. this will probably have to be done slowly to prevent fracture.

[add comment to indicate how stupid the trained technicians are.]

[further stipulate how much smarter I am.]

[include derisive comments toward other commenters.]

[ego inflation +1]

Even aluminum acts weird in an MRI room. Take a large aluminum plate and try and move it inside the barrel of an MRI... it's SLOW MOTION, impossible to move quickly with any force.

How much you want to bet that this episode began with Bubba, Junior, and Jethro all saying "Hey y'all watch this!"

Looks like it's been mentioned, but one doesn't simply "turn off" an MRI. Ramping down an MRI may mean a full day (or more) of downtime and a call to the vendor to send out an engineer to administrate the ramp down and ramp up, which isn't cheap. Some MRIs have an Emergency Quench that will kill the field quickly (within minutes), but it can result in irreversible damage to the coil, so their use is recommended only when someone's life is threatened by an object pinning them to the machine.

I have a titanium plate held in with stainless steel screws in my neck, and I've been inside an MRI several times without incident.

Not particularly surprising, as titanium and surgical stainless steel are not particularly magnetic, or downright non-magnetic. If I'm not mistaken, though, they can still produce significant imaging artifacts.

"MRI"? More junk science. It's obviously demonic chair possession.

whats all this science talk about? im a radiology tech, they teach you in school that MRI runs on pure black magic. everyone knows that, pfft.

also, the junk in your neck does indeed produce some righteous artifact.... like its pretty pointless to ever get a CT scan of your neck.

i dont understand how that chair got anywhere near the MRI in the first place. everywhere ive ever worked has had specialty items for MRI. special chairs, stretchers, wheelchairs, oxygen tanks, etc. and the room where the techs sit their butts is not the room where the patients are scanned. wierd.

>> ^JohnChrist:
>> ^charliem:
Turn the MRI off maybe ?

Except that it's a magnet. You can't turn off magnets..


Thing is, it's an electromagnet.

the chair died yesterday. complications arose due to an un-diagnosed armrest tumor.

charliem, this is actually the most informative and thought-provoking discussion that I have read on VS in a very long time.

As an MR researcher, the 'Why don't you just turn off the magnet' complex is a safety issue we battle everyday. It's easy to make mistakes , even if properly trained, because you can't see the magnetic field, and by the time you feel it, it's often too late. Almost every MR researcher I know has had their credit cards wiped (at least once) by forgetting their wallet in their pockets when they go grab something from the MR suite. This case is more serious but luckily it looks as though no one was injured.

To clear things up, clinical MRI's use Superconducting Electromagnets. After installation, the current is slowly ramped up until the desired field strength is reached but they *DO NOT* require additional power to keep them running. There is NO power cord for the magnet and the current will run FOREVER so long as the coil is kept cool enough to remain superconducting (usually using liquid helium as mentioned previously).

An enormous amount of energy is released when a magnet "Quenches" i.e. heats up and becomes non-superconducting. Once the coil has non-zero resistance a ton of heat is generated, the liquid helium boils off, and the coil can expand causing permanent damage to the magnet. Furthermore, when the helium gas boils off it can displace all the oxygen in the room creating another hazard: asphyxiation.

While most systems have a "Quench" button which has been engineered to be as friendly as possible to the magnet, it is a costly and risky maneuver which is reserved for cases when human life is in danger i.e. someone walks in with a non-MRI safe gurney which pins someone to the magnet... It has happened.

The point is, this is not a magnetic field that can switched off easily/cheaply and turned back on quickly/cheaply!!

As for metal implants, it is important to remember not all metals are magnetic, and most implants are made of MRI Safe materials i.e. won't rip out of your skin in the presence of a strong magnetic field. However, most are not "MRI Compatible" meaning they will cause image artifacts in a small area around their location.

MRI is safe, working with humans around an MRI is the dangerous part.

What he said... except the part about asphyxiation.

You have be in basically a sealed off room to die from helium. I have been working for cryogens for 9 years, and while I have always heard *you can die from the gas* it is a little ridiculous with helium. It is lighter than air so it will float to the top of the room and escape to the atmosphere.

Maybe us physics people are crazy, or it is the physical size of our magnets, or we just know how to fix them when they go bad... but I always just ramp the temperature when I want to kill the field. And you can ramp the current to change the field. This I have done.

at my hospital they built the dr's office/outpatient procedure building AROUND our magnet. its an 8 story building. magnet on the 4th floor. when the magnet goes, its gone. a major dallas hospital without an MRI..........
we look like chumps!

>> ^MycroftHomlz:
What he said... except the part about asphyxiation.
You have be in basically a sealed off room to die from helium. I have been working for cryogens for 9 years, and while I have always heard you can die from the gas it is a little ridiculous with helium. It is lighter than air so it will float to the top of the room and escape to the atmosphere.
Maybe us physics people are crazy, or it is the physical size of our magnets, or we just know how to fix them when they go bad... but I always just ramp the temperature when I want to kill the field. And you can ramp the current to change the field. This I have done.


Thing is, its not just helium thats doing the cooling.
A lot of MRI's also use Nitrogen to mediate the temperature between the helium / wire, and helium / atmosphere barrier to prevent cracks in the containment chamber, and unwanted condensation near the electronics.

If a quench occurs, it will release both gasses into the room in the event of a ventilation failure. If you enter the MRI room without leaving the door open, the pressure differential created by the quench can create enough force on the door to prevent you from opening it, causing you to be stuck in a room with a quickly diminishing supply of O2.

Thus...you die.

Always leave the door open when you are using the room.

http://www.videosift.com/video/What-NOT-to-do-with-metal-objects-and-MRI-machines-10s

*short

This video has been flagged as being less than 1 minute in length - declared short by maatc.