# How can they run MRI's in a crowded hospital? **URL:** \ **Category:** Factual Questions\ **Created:** [June 13, 2008, 8:35pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853 "2008-06-13T20:35:14Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Mr\_Buttons](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@Mr\_Buttons](https://boards.straightdope.com/u/Mr_Buttons)\ **Post date:** [June 13, 2008, 8:35pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/1 "2008-06-13T20:35:14Z")
Inspired by the thread: [What would a magnet do to my laptop?](http://boards.straightdope.com/sdmb/showthread.php?t=471655) I’m not an expert on EMFs or anything, but aren’t MRI machines just about the biggest man-made EMF producers? How can we run such strong magnetic fields near all of the expensive/super-sensitive computers/machines. You can’t wear jewelry/wristwatches/etc. around them because it has enough power to rip them off your body, your arm/skin in the way being of little consequence to the EMFs. At least that’s what I’ve heard. So how does something putting out those kind of EMF waves, around ALL the sensitive medical equipment within the same building, NOT damage the computer monitoring equipment? I’m guessing that they have a lead shield or something, but I don’t know if lead blocks EMF’s. Sorry for rambling, but any opinions to enlighten me are much appreciated. 🙂 ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [June 13, 2008, 8:47pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/2 "2008-06-13T20:47:41Z")
[Faraday Shield](http://en.wikipedia.org/wiki/Faraday_shield) > [@](#): > > To a large degree, Faraday cages also shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the radiation’s wavelength. ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [June 13, 2008, 8:53pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/3 "2008-06-13T20:53:16Z")
The two MRIs I’ve seen in local hospitals are isolated in their own buildings. ---
**Author:** ![Mr\_Buttons](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@Mr\_Buttons](https://boards.straightdope.com/u/Mr_Buttons)\ **Post date:** [June 13, 2008, 8:59pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/4 "2008-06-13T20:59:07Z")
[QUOTE=Santo Rugger] [Faraday Shield](http://en.wikipedia.org/wiki/Faraday_shield) [/QUOTE] Cool, very interesting. That’s pretty much all I needed. Thanks. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [June 13, 2008, 9:14pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/5 "2008-06-13T21:14:52Z")
[QUOTE=Mr Buttons] Cool, very interesting. That’s pretty much all I needed. Thanks. [/QUOTE] No problem. FWIW, IIRC the holes in the cage when I had an MRI on my knee a couple months ago were about 1mm diameter, spaced about 1.5 mm apart. A solid ferrous metal would block the magnetic field, too, but I don’t know how it would interact with lead or aluminum. ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [June 13, 2008, 9:30pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/6 "2008-06-13T21:30:36Z")
[QUOTE=Mr Buttons] Cool, very interesting. That’s pretty much all I needed. Thanks. [/QUOTE] I realize that the answer has been obtained, but I thought I’d add tuppence. The faraday cage at my hospital’s MRI had gone bad - we could tell because the images were getting degraded, due to random radiowaves being received by the MRI. One of the cheap ways to test for field integrity is to go into the MRI suite with a portable radio - If you get a station, your faraday cage has gone wonky. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [June 13, 2008, 9:40pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/7 "2008-06-13T21:40:34Z")
[QUOTE=Attack from the 3rd dimension] I realize that the answer has been obtained, but I thought I’d add tuppence. The faraday cage at my hospital’s MRI had gone bad - we could tell because the images were getting degraded, due to random radiowaves being received by the MRI. One of the cheap ways to test for field integrity is to go into the MRI suite with a portable radio - If you get a station, your faraday cage has gone wonky. [/QUOTE] Any idea how a Faraday cage goes bad? It seems to me that it would have to be an actual physical breakdown of the structure. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [June 13, 2008, 10:02pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/8 "2008-06-13T22:02:01Z")
The strong magnetic field in an MRI is pretty much static, and Faraday cages don’t block static magnetic fields well. From the linked article: > [@](#): > > A Faraday cage will not shield its contents from static magnetic fields. I suspect the main “shielding” is just distance from the machine. The fields will fall off as 1/r^3. Presumably, an MRI machine needs the Faraday cage to block RF fields from interfering with its operation. > [@](#): > > Any idea how a Faraday cage goes bad? I’d guess there are doors that have to be closed to complete the cage, and that they have contacts that are corroded, or bent. Either that, or seams (maybe where walls meet) have come loose. ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [June 13, 2008, 11:11pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/9 "2008-06-13T23:11:38Z")
You can shield it with [mu-metal](http://en.wikipedia.org/wiki/Mu-metal), but it isn’t cheap. ---
**Author:** ![Attack\_from\_the\_3rd\_dimension](https://avatars.discourse-cdn.com/v4/letter/a/b38774/32.png) [@Attack\_from\_the\_3rd\_dimension](https://boards.straightdope.com/u/Attack_from_the_3rd_dimension)\ **Post date:** [June 13, 2008, 11:43pm UTC](https://boards.straightdope.com/t/how-can-they-run-mris-in-a-crowded-hospital/452853/10 "2008-06-13T23:43:32Z")
[QUOTE=Santo Rugger] Any idea how a Faraday cage goes bad? It seems to me that it would have to be an actual physical breakdown of the structure. [/QUOTE] It starts off with hanging around the pool hall drinking beer, then turns to marihuana, or “weed”, which is the gateway to “hard stuff”. The main protective aspect of the magnetic field is in fact distance, and the cage is primarily to prevent RF interference, as mentioned above. In our case, the MRI suite is in the periphery of a much-remodeled building which has had multiple leaks and such. I suspect that it was leaks and corrosion, as they had to rip out most of the walls - around the massive magnet - and rebuild them. They upgraded the magnet while they were there. An unrelated idea for a movie: Tony Soprano type gets part interest in a private MRI clinic. He builds a secret room behind the magnet, within the faraday cage, so he can use it as a safe discussion room. All remote EM transmissions are blocked by the cage, magnetic tape is made useless by the magnetic field. When the bad guys come to kill him, he breaks through the false wall into the MRI suite, and hilarity ensues. Patient runs for its, pistols get sucked into magnet bore, steel jackets slugs curve into the magnet, liquid nitrogen goes squirting around. If you make the movie, just say “Thanks, Attack from the 3rd Dimension”.