8 ms·
Metal chair near MRI machine
- lutorm 16y agoI didn't realize they were on all the time.
- jarin 16y agoYou know how it takes months to power up and down the Large Hadron Collider? MRI machines are kind of like a mini version of that.
- retube 16y agoand it takes weeks to power them down too, else you get the dreaded quench... http://en.wikipedia.org/wiki/Superconducting_magnet#Magnet_quench http://en.wikipedia.org/wiki/Superconducting_magnet#Magnet_q...
- mbateman 16y agoYes, you can't even turn them off by unplugging them, as it were. A certain kind of emergency shutdown dumps the helium needed to allow superconductivity (and thus maintain the magnetic field). It costs like $20,000 to do this and is quite dangerous in itself.
- india 16y agoIt's called MRI quenching and dangerous it can be[1]. [1] http://www.youtube.com/watch?v=1R7KsfosV-o http://www.youtube.com/watch?v=1R7KsfosV-o
- InclinedPlane 16y agoModern high-field superconducting MRI magnets can hold tens of megajoules of stored magnetic field energy, equivalent to the explosive energy in several kilograms of TNT.
- lutorm 16y agoYeah, I should have thought this through. I knew you kept them cool, and with a bit of thinking it should have been clear that you don't turn a superconducting coil off, since nothing's powering it... ;-)
- glabifrons 16y agoThey're not. They're only magnetic when they are in operation. I've been in them, I've been with people who've been in them, and my family is in the medical field. If they were fully energized all the time, you wouldn't be able to bring people in and out of the room on a stretcher.
- mbateman 16y agoI'm not an MRI tech but I work on MRI image analysis academically, so I know a bit more than usual by hearsay and I see them used all the time. Why are there "MRI magnet is always on" signs in the medical imaging areas of the med school here? Are you sure they don't use titanium stretchers near the field? Why do they perpetually supply the MRI with liquid helium? My understanding is that even when they are not used there is a field of between 1 and 3 teslas, depending on the scanner. (A quick google search for things like "mri magnet is always on" and "mri safety" and such seems to confirm this.) Edit: Also, you can get closish to the scanner with a ferromagnetic object without a problem. The field doesn't encompass the whole room or anything. 10 or 15 feet away will be fine.
- glabifrons 16y agoI apologize, I should clarify my point. They're not magnetic enough to pull a chair off the floor or things across the room (as the story indicates) when they are not in operation. You can walk around the room with your watch on (for example), but if they fire it up and you're in there with it, it's destroyed. Just look how close they have to get the steel oxygen bottle to the center (in the video linked above) before it moves. It's almost inside it already.
- kressler 16y agoThere are low field scanners that use conventional electromagnets, which aren't always on. However, the scanner shown is a 1.5 Tesla (T) or 3T scanner (difficult to say which from just the housing), and the main magnetic field is always on. The main field is supplied by a superconducting ring immersed in liquid helium. As a previous poster noted, the only way to shut one down is to dump the helium, and the cost to bring the scanner back up is in the tens of thousands of dollars. There are smaller electromagnets involved to apply field gradients across the bore of the scanner (on the order of 50 mT/m) which are off when the scanner is not operating, but these are quite small compared to the main field. My Ph.D. dissertation was on data acquisition and reconstruction techniques for MRI. I've logged hundreds of hours operating high field scanners like the one shown, and dozens of hours being scanned for various research studies. I've also (carefully) hauled a variety of strange things in and out of scanner rooms. Most of the tools we used were non-ferrous, and we had to be extremely careful with the few ferrous pieces of equipment we had to use. The magnetic field does drop off rapidly as you move away from the scanner, so objects more than 10 feet or so away are unlikely to be pulled in.
- js2 16y agoDepends on the MRI magnet type apparently, but with modern superconducting magnets, yes: http://health.howstuffworks.com/mri.htm/printable http://health.howstuffworks.com/mri.htm/printable http://en.wikipedia.org/wiki/Superconducting_magnet#Persistent_mode http://en.wikipedia.org/wiki/Superconducting_magnet#Persiste...
- deleted 16y ago[deleted]
- anthonyb 16y agoLots of fun pictures on that site, eg. http://www.simplyphysics.com/flying_objects/FloorPolisher.JPG http://www.simplyphysics.com/flying_objects/FloorPolisher.JP... Which looks like it might be a bit harder to remove...
- jafl5272 16y agohttp://www.simplyphysics.com/flying_objects/acetylenetorch.html http://www.simplyphysics.com/flying_objects/acetylenetorch.h...
- anthonyb 16y agoand http://www.simplyphysics.com/flying_objects/Chair_Removal.flv http://www.simplyphysics.com/flying_objects/Chair_Removal.fl... to give you some idea of how hard they "suck" - that's two guys (one with a lever) plus some sort of strapping so that people in another room can pull too.
- jonsen 16y agoTakes an iron man to do it. He is in the other room ;-)
- joezydeco 16y agoHere's a steel bottle getting sucked in http://www.youtube.com/watch?v=7g5UVrOt2CI http://www.youtube.com/watch?v=7g5UVrOt2CI
- thunk 16y agonom nom nom Edit: Oooh, yeah. Make it hurt.
- deleted 16y ago[deleted]
- naz 16y agoIt is refreshing to see such a candid writeup emerge from such a normally lawsuit-fearing industry.
- gridspy 16y agoI guess it helps that no patients were injured in the accident.
- ars 16y agoA gun flew into a machine and dischared with the safety still on! http://www.simplyphysics.com/flying_objects/GuninMagnet.html http://www.simplyphysics.com/flying_objects/GuninMagnet.html
- derefr 16y agoNow that's something I'd like to see on MythBusters. (Though not necessarily with an MRI machine—those things cost more than their entire budget. A large ferromagnetic coil would do nicely.)
- gridspy 16y agoAwesome explanation of the physics of why the gun discharged here (http://www.ajronline.org/cgi/content/full/178/5/1092 http://www.ajronline.org/cgi/content/full/178/5/1092) Short summary: - A round was chambered in a safety locked gun. - The "Sear" at the top of the gun that normally moves when the gun is fired was locked, and the empty cartridge was still in the gun, confirming that the gun was physically locked - The pin was pulled into the unlocked firing position by the magnetic field - The impact of the gun when it hit the CT caused the firing pin to move against the spring and hit the back of the loaded bullet, causing it to fire. There is white paint on the front of the gun where the gun hit the CT confirming the impact point
- Zak 16y agoGood summary, but it doesn't quite make it clear what safety device failed. The firing pin block exists to ensure that an impact in-line with the firing pin cannot move it when the trigger is not depressed. It too could be moved by inertia, but its movement is perpendicular to the firing pin itself, so an impact cannot move both at once. In this case, the magnetic field moved the firing pin block, while inertia pushed the firing pin forward relative to the rest of the gun. This is the only time I've ever heard of a firing pin block failure resulting in an accidental discharge.
- epochwolf 16y ago> This is the only time I've ever heard of a firing pin block failure resulting in an accidental discharge. The is the only time I heard of a gun encountering an extremely powerful magnetic field.
- tocomment 16y agoIt's weird to think that in 20 to 30 years well have magnetic fields this strong in every day devices. I wonder how we will deal with issues like this.
- carterschonwald 16y agowhat sort of devices are you thinking about? Pocket fusion reactors and other sorts of plasma bottling tech?
- rbanffy 16y agoTime machines, of course. http://en.wikipedia.org/wiki/John_Titor#Time_machine http://en.wikipedia.org/wiki/John_Titor#Time_machine
- tocomment 16y agoHow about a portable MRI for starters? You could possibly use it a brain computer interface. You could also perhaps use transcranial magnetic stimulation to send data into your brain? (Just some wild thoughts). On the more mundane side, you could use the diamagnetic effect of high magnetic fields to deflect water from windshields, keep snow off your driveway, give your tires traction on ice. You could even hover over water. I'm sure there are lots of other applications I'm overlooking.
- deleted 16y ago[deleted]
- tocomment 16y agoWhy all the down votes? If these ideas are flawed why not explain it? How are ideas for the application of magnetic fields not in the spirit of hn?
- hugh3 16y agoI think the downvotes are for the unsupported assertion that in 20-30 years we'll have magnets this strong in everyday devices. This seems unlikely, for various reasons.
- zweben 16y agoThey should buy some plastic chairs.
- kree10 16y agoReminds me of a story I read years ago (can't find a working link) of how the IT staff at a hospital would routinely wipe hard drives by just taking them into the MRI room. Once, one of them decided to save time by not removing the drive from the PC first, and you can probably guess the rest.
- mkramlich 16y ago... they had to wipe the PC off the MRI? Or wipe the IT staff off the MRI/PC?
- mkramlich 16y agoI hope the MRI's don't run Windows. Then they'd have two problems.
- kressler 16y agoSome of them do run Windows on the console the operator the uses. Some run Linux, and some of the older generation scanners used SGI workstations. They run various RTOS's on the systems that actually control the scanner.
- cgomez 16y agoI thoroughly enjoyed your reply as it offered useful information while also making the original commenter look silly.
- mkramlich 16y agoI did not enjoy your reply as it did not add anything useful, and overlooked the fact that the comment you considered silly was intended as a joke. Dismissing something funny as silly is a bit like dismissing water as being moist. ;)
- enntwo 16y agoOn a Windows/Hospital related note, I heard this antecdote in a class, any confirmation if true or source? Seems very plausible and likely. During an operation, one of the OR monitoring devices went down because it was running on Windows and was neglected for some period of time, causing Windows to do an automatic reboot for a "Critical Windows Update." Of course, seeing a necessary piece of OR equipment go down due to a Windows setting didn't make anyone happy, so the response was to remove automatic update from all of the Windows boxes in the Hospital. Not just mission critical ones, all of them: Secratary's machies, Nurse's machines, IT machines, etc. Fast forwood some months/years, no manual updates were done either, and with automatic ones turned off, a virus came across through a worker's computer and wiped out everything. True or not, I still think it is a good story for how not to handle security issues.
- techiferous 16y agoReminds me of neodymium magnets, which can be so strong that you have to plan your route through a room when transporting them: http://www.wiredpakistan.com/forums/viewtopic.php?id=4895 http://www.wiredpakistan.com/forums/viewtopic.php?id=4895 http://cgi.ebay.com/350-lb-Rare-Earth-Neodymium-Magnet-INDUSTRIAL-FORCE-New-/220615966201?cmd=ViewItem&pt=LH_DefaultDomain_0&hash=item335dbc7df9#ht_3753wt_1242 http://cgi.ebay.com/350-lb-Rare-Earth-Neodymium-Magnet-INDUS...
- whatwhatwhat 16y agoThis is a great link... My father is a Radiology Engineer and I will defiitely be sending this his way.
- Confusion 16y agoI've had this kind of thing happen to me when I was graduating in physics. I was working with a liquid helium based refrigerator that had a superconducting magnet inside it, pretty much the same technology used in MRI. The setup could reach fields up to 13T and the old CRT display that accompanied the setup would visibly skew above ~6T (it was pretty close to the magnets). I was sitting on a small wheeled stool of which two varieties floated around the labs: one with metallic wheels (red) and one for use near these setups (blue). Unfortunately, one of the wrong ones had found its way into this lab, but do you normally pay attention to the color of stools? I sat down, probably around a meter from the setup, cranked up the magnetic field, stood up to adjust something and BANG, the stool collided with the fridge. Luckily nothing was damaged, but the reason for these two types of stools was suddenly very clear to me :)
- retube 16y ago13 Tesla? That sounds a lot. would make it just about one of the most powerful magnets in the world. I would have thought 6T would vaporise a TV set, not just distort the image. E.g the ATLAS magnet is 4T and requires 21,000 amps to power it.... http://public.web.cern.ch/public/en/spotlight/SpotlightATLAS-en.html http://public.web.cern.ch/public/en/spotlight/SpotlightATLAS...
- Confusion 16y agoIn 2001 it would have been a world record, but by 2005 those kinds of superconducting magnets had become pretty regular pieces of equipment, at least for the kind of nanophysics lab I was in. You should realize it creates that field only inside a small space with a diameter of a few cm. The entire thing is suspended in liquid helium, including the samples on which we did measurements. I believe we estimated that, at a meter from the magnet, the field had dropped to something like 3T. I'm not sure how much power it drew, but I seem to recall it was plugged into a regular socket.
- Rufus 16y agoThe dueling speculation with regard to how close (or far) you need to be from an MRI scanner ignores a few points. First, the attractive (translational) effect is not strictly a result of the strength of the magnet, it is a product of the magnet strength and the magnetic spatial gradient (or, by analogy, the 'steepness' of the magnetic field). Contemporary MRI scanners use what's referred to as 'active magnetic shielding' which means that the magnetic field is 'girdled' and held closer to the scanner than it would be if we just let it follow the cube-of-the-distance drop-off rate. This increases the 'steepness' of the magnetic field, but pulls it closer to the body of the instrument. One of the major factors regarding attractive force is the object that is being pulled. The longer it is (not so much the 'bigness' but the length), the greater the potential pull. The attractive force is a result of the difference between the magnetic field as experienced by one end of an object and the field at the other end. The greater the difference (a product of the steepness of the field and length of the object), the stronger the attractive force. So, theoretically you could take a 2D ferromagnetic filament and, if you turned it so that it didn't cross any of the magnetic flux lines, the attractive force would = 0. Keeping the center in the same location but rotating the filament so that it crossed flux lines, presto, attractive force! If you're looking for more information about magnetic projectile accidents, I suggest you check out http://mrimetaldetector.com/blog/2010/02/mri-projectile-accidents-one-exemplar/ http://mrimetaldetector.com/blog/2010/02/mri-projectile-acci... and the other posts.
- blahblahblah 16y agoRufus knows what he's talking about. A conventional 1.5T or 3T clinical scanner with active shielding makes the danger zone of the fringe field more compact, but also makes the transition zone between where a ferromagnetic object experiences little force and where it experiences intense force that makes it a dangerous projectile quite small in space (and therefore quite difficult for a human being to predict). If you've got a ferromagnetic object within the 5 gauss line on a modern clinical system, you are playing a dangerous game of chicken. On a system without active shielding, that transition zone is more gradual. The quoted field strength of a magnet can be very deceptive. That number indicates the strength of the field at the magnet's isocenter. It says absolutely nothing about the characteristics of the fringe field. There are small 9T animal magnets that you can work on with a steel crescent wrench and 1.5T magnets that you wouldn't dare to even consider walking in the room with ferromagnetic tools.
- Rufus 16y agoBTW: A few companies that make MR spectrometers for laboratory research sell 900 MHz systems, which are = 21 Tesla (and change). People MRI's are a whole lot weaker than many research magnets out there, today.