It's a poltergoost!

August 20, 2005 3:42 AM

Sucked in! MRI scanners are hungry for any metal objects in the nearby vicinity, with hilarious and sometimes tragic results. The roughly 10,000 scanners in the United States are found not just in hospitals, but in storefront clinics and even mounted on trucks, making rounds of small hospitals or parking at malls to do scans for a fee.
posted by asok (49 comments total)

MRI is not reccomended for those with magnets in their fingers.
posted by asok at 3:50 AM on August 20, 2005

"Shrapnel and machine-shop debris can also cause problems. In the 1990's, one patient was blinded in an eye when a metal sliver in it from an earlier accident moved."

I think most hospitals have metal check bays for patients prior to use to prevent this sort of thing happening. I say this in case anyone is worried about having metal in their body they don't know about and they need to have an MRI.

Lighting an MRI unit is a bit of a headache too, I can tell you.
posted by nthdegx at 4:01 AM on August 20, 2005

Wow this is horrible, because it's so avoidable.
posted by parallax7d at 6:09 AM on August 20, 2005

Ack! I was in an MRI some time ago and i'm glad I didn't get hit by anything metallic.

Don't they check the MRI rooms to make sure nothing metallic is there?
posted by divabat at 6:15 AM on August 20, 2005

I had an MRI done on my knee last week. The scan took over an hour, and the tech explained it was because they have a weak magnet. Nonetheless, it was installed in a big metal mesh cage, presumably to avoid accidents with metal elsewhere in the room.
posted by tippiedog at 6:27 AM on August 20, 2005

I used to work for an NMR company (up to 25 Tesla supercon magnets) doing service engineering. More than once flying screwdrivers and X-acto knives narrowly missed my head. I did get my keys grabbed more than a few times. And credit cards wiped.

Something they don't mention in the NYT article is that sometimes when metal objects are in the vicitinty of these things is they disrupt the stability of the magnetic field inside the coil and current hot spots can occur. These hot spots literally heat up an isolated area and can raise the temperature (helium is liquid below 4K, or -458F) enough to cause the coil to lose its superconductivity. These things operate with an incredible amount of current coursing through them and without the superconductivity the coil heats up and boils off the liquid helium and nitrogen blasting super-cold gas into the room. Really loud and quite alarming. And expensive.
posted by RockCorpse at 6:34 AM on August 20, 2005

ARGGHH
posted by zouhair at 6:58 AM on August 20, 2005

nthdegx, how do the metal check bays work? Since i read in the NYT article that tattoos with iron oxide ink, present risks, they'll have to be pretty damn good these days, huh? I mean how do you check that?
posted by dabitch at 7:00 AM on August 20, 2005

They warned me about metal. But they did not say one word about the noise. Who expects high-tech to make mechanical noises? I lay very still in the damn thing, but quite scared that it was about to fall apart! Afterwards I researched it, and refused to return. This was in Germany, and I wasn't much interested in dealing with the nasty-tempered German women running it anyway. My single worst experience in 5 years of living in Germany. (which actually speaks well for the place, and I miss it).
posted by Goofyy at 7:01 AM on August 20, 2005

I'm happy we only have a few of these in the city of Montréal. The waiting lists are so long that people just die while on the waiting list.
posted by kika at 7:17 AM on August 20, 2005

I've had two. They both warned me about the metal, and made sure I took my shoes off because shoes often have little metal pieces in the soles. At the second and most recent (2004), they went so far as to make patients change into a full hospital get-up - paper top and pants. Maybe people had too many problems with rivets in their jeans?

The first one warned me about noise, so that wasn't a problem. And then there's this, that they also don't tell you about.


posted by dilettante at 7:24 AM on August 20, 2005

At the hospital where I got my head MRI, it was standard procedure to give valium to anyone sticking their head in the tube to avoid claustrophobic freak outs. Needless to say, I don't remember much of the experience. I remember it was loud though. Reeeaaallllyyyy loud.

I wonder what happens to patients with metal screws holding bones together and such? Do they get eaten by the magnet or what?
posted by grapefruitmoon at 7:49 AM on August 20, 2005

The metal-mesh room is more to isolate the disruptive effect of NMR on other hospital equipment than to keep metal from being attracted to the magnet.

The loss of superconductivity is called "quenching" and is very dramatic. If the exam room is small, the helium boil-off creates thick clouds (yes, of water vapor) that start at the ceiling and can extend to the floor. If that happens, the prudent thing to do is leave, because the helium can displace enough breathable air to cause unconsciousness. The odds against your seeing this are very high.

I believe people with metal pins, screws, or plates (or pacemakers, etc.) are prohibited from getting MRI scans.
posted by Kirth Gerson at 7:57 AM on August 20, 2005

Woah.
posted by Civil_Disobedient at 8:01 AM on August 20, 2005

Those crazy magnets. When will they learn?
posted by TwelveTwo at 9:03 AM on August 20, 2005

dabitch, presumably they work the same way other metal detectors work.
posted by nthdegx at 9:11 AM on August 20, 2005

I just had one this week. I had to put on a hospital gown and leave everything I brought with me in a locker. They quizzed me thoroughly about any injury that could have left metal in my body or surgery that may have involved staples. No oxygen tanks anywhere near the MRI room, it is pumped through the wall in there. They also gave me earplugs to help with the noise.

Still, it was a really unpleasant experience--being stuck in a tube for 45 minutes, told to remain completely still and asked to hold my breath repeatedly. I can totally see why they have special machines for "larger" people or those with claustrophobia.
posted by jrossi4r at 9:50 AM on August 20, 2005

I am putting on my chainmail and wielding my broadsword and setting out on my new quest to rid our lands of the MRI machine.
posted by DigDugDag at 9:53 AM on August 20, 2005

I get MRIs every year or two.

I much prefer an MRI to a CT scan. CT scans quite frequently involve intravenous contrast medium injections which are, frankly, slightly creepy: a warm, grainy fluid gets pumped into your arm and then slowly inches through your bloodstream with each heart beat. MRIs rarely require anything to improve contrast.

For much the same reason they can keep their PET scans too. MRI all the way.
posted by snarfodox at 9:55 AM on August 20, 2005

The most notorious accident was the death of 6-year-old Michael Colombini in 2001 at the Westchester Medical Center in Valhalla, N.Y. He was sedated in a scanner after a brain operation when his oxygen supply failed. An anesthesiologist ran for an oxygen tank and failed to notice that the one he found in the hall outside was made of steel. As he returned, the tank shot out of his hands, hitting Michael in the head.


That is undoubtedly the most distraught anesthesiologist is history. An awful tragedy.
posted by The Jesse Helms at 10:12 AM on August 20, 2005

The MRI technician warned me about the loud tapping and gave me ear plugs. I was asked if I had metal screws or plates. Was instructed to remove my earrings and watch, but not my rings?? I hated the claustrophobic feeling. In Oz no valium was offered. The seond time I asked for an eye patch to assist with the claustrophobia. Hopefully I won't have to have anymore MRI's. At least I didn't have to share the space with a chair or a buffer : - ).

The CT scan.....shocking migraine afterwards.
posted by Chimp at 10:41 AM on August 20, 2005

I saw the article in NYT, and so wasn't going to read this, but got drawn in.
posted by RelentlesslyOptimistic at 12:29 PM on August 20, 2005

A long time friend of mine was chief scientist at a major NMR research lab around the time the techniques to selectively image different tissue types were being developed. At the time I was very interested in 3D graphics and modelling techniques so he was able to sucker me into volunteering to have my head scanned with the promise I could have the datasets afterwards.

I went through the whole metal detector bit before being put in the machine and was told the story about the man who had one eye destroyed. Apparently he was a steelworker and was completely unaware he had a fragment of metal in his eye - until the magnet tore it out.

As others have noted it's not a very pleasant experience and, like Goofyy, I was unpleasantly surprised at just how noisy it was - you don't expect a high tech setup to leave you feeling like you're stuck in a metal pipe with a malevolent dwarf hammering on the outside.

All of that was nothing, though, compared to what happened afterwards. My friend brought up a somewhat crude yet realistic 3D model of my head on the computer (Yikes! are my ears really that big?) then he selectively removed the outer layers of my skin....

I decided I didn't want those models. Just knowing they were on my computer would have made me feel creepy!
posted by arc at 12:32 PM on August 20, 2005

Experiencing unforeseen difficulties on my mission. Over. Send well armored reinforcements pronto. Over.
posted by DigDugDag at 2:06 PM on August 20, 2005

"... it's so avoidable."

Isn't that precisely wrong? Small amounts of metal are so ubiquitous and mundane that it is only too easy to overlook them.
posted by i_am_joe's_spleen at 2:28 PM on August 20, 2005

Magnetically steering tissue-sampling catheters through the brain:

Dacey began the history-making operation by drilling a small hole, about the diameter of a pinkie finger, through the top of his patient's skull. As soon as the last bone fragments were swept clear, he temporarily closed the opening with a plastic bolt. Six small pieces of metal that would later serve as markers were then attached to the outside of the skull...

...With a safe route to the tumor mapped, the patient's head was placed in the MSS, where it was positioned between three sets of superconducting magnets. The plastic bolt that temporarily sealed the hole in the skull was removed. A tiny magnet attached to a guidewire, surrounded by a spaghetti-thin plastic catheter, was gently pressed against the patient's brain...

...The "pull" was provided by the attraction of a series of rapidly changing magnetic fields that the superconducting magnets created within the patient's brain. The head of the guidewire followed the advancing magnet field, slowly cutting a curved route to the tumor, in precise 1mm steps.

MRI is used during diagnosis to pinpoint the biopsy target. More details here and here.
posted by cenoxo at 2:43 PM on August 20, 2005

Jeez. I never realized how tiny those tubes are. If anyone thinks they are scanning me, they better have a bowl full of valium.
posted by dame at 3:16 PM on August 20, 2005

mythbusters episode 19 (link) looked at the tattoo-in-the-mri myth. If I remember correctly, they didn't any reaction with a normal one, so they tattooed pigskin with custom ink that had a huge amount of iron in it and still no reaction.
posted by concreteforest at 4:22 PM on August 20, 2005

Mythbusters is a great show, but I wouldn't take medical advice from them (dead pigskin isn't a living human being.) Better to listen to your radiologist:

...extensive tattoos and some kinds of make-up contain enough metal particles to have the potential to cause heat injury although this is rarely a problem.

MRI effects on tattoos (and permanent makeup like tattooed eyeliner) are rare and minor, but they're not a myth. From the report MRI Safety at the American Academy of Micropigmentation:

...a small number of patients (fewer than 10) have experienced transient skin irritation, cutaneous swelling, or heating sensations at the site of the permanent colorings in association with MR procedures. More recently, there has been one anecdotal report of a patient undergoing MR imaging who complained of a burning sensation at the site where a large tattoo had been applied on his arm using a black pigment.

Investigation of the incidents related to patients experiencing problems in relation to the presence of tattoos revealed that there was a tendency for the problem to occur whenever pigments that contained iron oxide or other similar ferromagnetic substance(s) were used. This includes those pigments that are especially black or blue in color.

Supposedly, certain ferrous pigments used for the tattooing process can interact with the electromagnetic fields used for MR procedures, producing the reported problems.

A recent case report indicated that 24 year old patient experienced a sudden burning pain at the site of a decorative tattoo while undergoing an MR procedure on the lumbar spine using a 1.5 T MR system. Swelling and erythema was resolved within 12 hours, with no evident permanent sequela. To permit completion of the MR examination, an excision of the tattoed skin with primary closure of the site was performed. Apparently, the tattoo pigment used in this case was ferromagnetic, accounting for the symptoms experienced by the patient.
posted by cenoxo at 5:27 PM on August 20, 2005

I can believe the magnetic-tattoo stories. One of the ways the government detects counterfeit money is by looking for the magnetic signature of the black ink in genuine currency. Apparently, the iron content of the ink was originally just an accident, but once they discovered it, they wrote it into the specification. So I can see where tattoo ink might have a similarly accidental iron content.
posted by Kirth Gerson at 6:00 PM on August 20, 2005

Where I work there is a girl who used to work at Austin Radiological Associates, a big radiology group here in town. She used to set up appointments for patients.

For the people too big to fit in the MRI (I think the weight limit was 400 lbs), they had a special facility in San Antonio they sent them to to be imaged.

Sea World. I am 100% serious. So basically, they treat you like a whale if you are that huge.
posted by beth at 7:39 PM on August 20, 2005

Tattoo ink can have some nastier metallic contents, including:

...Antimony, Arsenic, Beryllium, Cobalt, Lead, Lead compounds, Nickel and Selenium, collectively referred to as toxic metals, each of which is a toxic chemical that is known to the State of California to be carcinogenic and/or may result in reproductive harm.
posted by cenoxo at 7:52 PM on August 20, 2005

Why are the MRI machines so noisy?
posted by five fresh fish at 7:57 PM on August 20, 2005

People, two words: plastic chairs. I mean, most of the items in those machines were chairs, so it seems like a no brainer.
posted by e40 at 10:01 PM on August 20, 2005

I worked for a while around (and in) a hospital MRI unit. They are truly amazing machines which have opened new doors for medical research and treatment. All patients and those working near the units are given a very thorough screening interview. All recent implants (screws, plates, etc) are made of non-ferro-magnetic material but should still be discussed. People with tattoos were told that if they became uncomfortably hot, signal and they could exit the unit before any damage could be done. The real worry is older aneurysm clips or soft tissue implants as well as foreign bodies. People who had worked extensively with metal were ineligible for research studies (not medically necessary).

There was a case of a patient coming to the ER with neurological symptoms and intoxicated to the point of unintelligibility that required an MRI for diagnosis. No interview was possible but a forward thinking resident got an x-ray only to find a roofing nail deep in the patient's brain. An MRI could have killed him.

The thing to remember is that the magnet is maintained 24 hours a day. Shutting it off involves quenching the magnet and then restarting it is a multi-thousand dollar project. Patient accidents are tragic and require constant vigilance but many of the images above are due to untrained custodial and maintenance workers after hours.

I think that GE puts out a video with graphic depictions of the power of the magnets, which was required viewing on numerous occasions. They show a pipewrench released from 5 ft away piercing an entire cinder block at the bore of the magnet.

In short: staggering medical potential with risks that can be managed by vigilant staff and technicians.
posted by Corpus Callosum at 2:03 AM on August 21, 2005

Wow Corpus. Thanks for that addition. I had no idea they maintained the magnet always. The pipe wrench meets cinder block thing is awesome.

I'm kind of surprised that the powerful magnetic field doesn't make trouble with the electrochemical processes of the body. Although, clearly that fascinating discovery about depression and MRI contributed by dilettante indicates there is some effect. Perhaps so subtle, its been missed.
posted by Goofyy at 3:23 AM on August 21, 2005

My senior project involved designing a warning system for MRI centers to prevent this sort of accident. We toured a facility, and while they're very careful about removing ferrous objects from patients, the techs themselves often walk around with a big bunch of keys around their necks. Stuff like that. Our sponsor (an MRI equipment maker) told us that as far as he knows, MRI centers all use the line "our personnel are all highly trained and we've never had an accident" to say there won't ever be one.

One of the scenarios we kept in mind while designing was a fire in the scanning room, and the firefighters come in with their axes...
posted by casarkos at 8:38 AM on August 21, 2005

dilettante: odd that you'd mention the article. I went through the MRI after suppering panic attacks (at the time we didn't know it was just panic attacks so we had to rule out everything else first). That day I was diagnosed with panic disorder and depression.

I was very uncomfortable and fidgety in the MRI; it certainly did not please me.
posted by divabat at 9:52 AM on August 21, 2005

So why not just knock yourself out, duct-tape your head in place, and 'wake me when it's over'? You need to stay awake and in voice contact with the MRI operator throughout the procedure.

Besides risks from ferromagnetic metal, the UCSD document Safety Guidelines for Conducting MRI Experiments Involving Human Subjects (375kb PDF) mentions that "In high magnetic fields, rapid motion of the head can cause dizziness, vertigo, nausea, or a metallic taste." This is one reason why you're moved slowly into (and should remain still while inside) an MRI scanner.

Your body tissues are heated slightly by the scanner's radio frequencies. Scans are adjusted to your body weight to minimize this, a heat sensor in the scanner core monitors your temperature, and the room is kept at 70º or less. The rapidly cycling magnetic field may also cause uncomfortable "stimulation in peripheral nerves, muscle, and blood vessels", resulting in headaches, tingling, skin overly sensitive to touch, or muscle twitching. If you feel any discomfort, say so.

Noises over 120 dB may occur "when current is pulsed through a gradient coil sitting in a magnetic field it acts somewhat like a loudspeaker, creating a sharp tapping sound at the characteristic frequency of gradient pulsing (around 1 kHz). The sound levels are most intense during dynamic imaging that requires rapid gradient switching." Earplugs can be worn, but music headsets have wires that can heat up in the electromagnetic field (not a good idea). For the same reason, tattoos/permanent eyeliner with metallic inks may cause skin irritation.

In case of fire, the UCSD MRI facility has white extinguishers made of non-ferrous materials, and "red extinguishers should not be taken into the magnet room." If firemen need to take in ferromagnetic tools, the scanner's magnet must be quenched first, or there may be more flying axes than a lumberjack contest...
posted by cenoxo at 12:45 PM on August 21, 2005

If the magnet has to be quenched before firefighters can enter, there will most likely be no fire when they do. Helium expands to seven hundred times its liquid volume when it changes to gas, and that is going to starve any fire in the exam room.
posted by Kirth Gerson at 2:03 PM on August 21, 2005

A few years ago one of our anesthesiology residents took the wrong anesthesia machine into the MRI room to anesthetize a patient for a scan (this is done routinely for children who can't remain still for the time needed for an exam and adults for whom Valium is not enough) and ended up with the machine stuck to the side of the scanner. Fortunately no one was hurt, buth the magnet had to be quenched (non-emergently) and it took two days to drain off the liquid helium, inspect/repair the machine, refill the magnet, and power it all back. Now the special non-ferromagnetic anesthesia machine is kept in the MRI room at all times. My biggest concern is that the crash carts are full of things that are not MRI compatible and in an emergency someone may forget that and bring one into the room, rather than taking the patient to the cart.

The metal cage around the MRI room mentioned above is not for the magnet, rather it is a Faraday cage to protect the sensitive radio equipment in the scanner from stray radio waves
posted by TedW at 2:39 PM on August 21, 2005

One more MRI story: we had a child with a possible brain tumor who needed an MRI but had multiple crowns on his teeth. While these were safe, they would have degraded the images beyond the point of usefullness. So we anesthetized the child, his dentist removed all the dental work, we moved him to MRI, did the scan, went back to the dental room to have the crowns replaced, and woke him up. At least that was how it was supposed to work. When we went to do the scan it was still distorted; a thorough search for stray safety pins, paper clips, and so on turned up nothing. Mom couldn't think of anything at first, but eventually recalled that a couple of years earlier his brother shot him with a BB gun. At the time all mom saw was a pinhole sized cut, but it turns out he had a BB in his cheek. We ended up redoing the dental work, a few week later a plastic surgeon had to operate to remove the BB, and when he had healed from that, we were finally able to do the whole dentist-MRI-dentist again procedure described above. What a struggle just for an MRI.
posted by TedW at 2:50 PM on August 21, 2005

Are there any nasty side-effects to having one's body subjected to huge, pulsating magnetic fields?

Ted: replaced the dentalwork with ceramics, I should hope. No need for metal fillings.

Aside: I'm rather surprised it's proved so difficult to keep major metal items outside the MRI room. I'd have thought SOP would be to identify everything that might be commonly needed, and ensure a non-magnetic version were available in the room; and to have a double-doored entry with a helluva metal detector and an buzzer/strobe alerting anyone passing the first door with metal on their person.
posted by five fresh fish at 6:45 PM on August 21, 2005

Kirth Gerson: it usually vents to the outside atmosphere.
posted by polyglot at 7:57 PM on August 21, 2005

fff: Are there any nasty side-effects to having one's body subjected to huge, pulsating magnetic fields?

Maybe. This primer from the FDA's Center for Devices and Radiological Health mentions some possible MRI side effects:

4.2 Pulsed Gradient Magnetic Fields

Another component of the MR environment is a pulsed gradient magnetic field that is used for signal localization. When this gradient magnetic field is applied, the magnetic field intensity changes rapidly, giving rise to a time-varying magnetic field. During the rise time of the magnetic field, a voltage is induced in an electrical conductor, even when it is stationary in the field. However, in most MRI systems, the currents induced by the pulsed magnetic gradient field are about 1,000 times smaller than those induced by the pulsed RF component and are therefore not of great concern with regard to thermal injuries.1 Major concerns with the pulsed gradient fields are biological effects including electrical nerve stimulation and the generation of light flashes (magnetophosphenes) that may result from a slight torque exerted on the retinal cones. Current FDA guidance limits the Time Rate of Change of Magnetic Field (dB/dt) to levels which do not result in painful peripheral nerve stimulation.

All seriousness aside, if you end up embedded in the machine, we'll bring you lunch while we try to get you out, OK? A nice, hot lunch:

4.3 Pulsed Radio Frequency Fields

A third main component of the MR environment is the pulsed radio frequency (RF) magnetic fields which is used to elicit MR signals from tissue. With regard to biological effects, one main concern with this component of MR is the production of heat in tissue. The rate at which RF energy is deposited in tissue is defined as the specific absorption rate (SAR) which is measured in units of watts per kilogram (W/kg). Current FDA guidance limits SAR whole body exposure to 4.0 W/kg for patients with normal thermoregulatory function and 1.5 W/kg for all patients, regardless of their condition. The duty cycle on the RF pulse during MR imaging is restricted based on this SAR limit.

With regard to medical devices, electrical currents may be induced in conductive metal implants, such as skull plates, and hip prostheses. When conductive patient leads are used during MR scanning, it is especially critical that no loops are formed by the leads. Looped patient leads or devices such as the halo device used for spinal immobilization can pick up RF energy resulting in induced currents, heating of the material, and as a result, potentially severe patient burns. To further reduce the possibility of burns, it is recommended to thermally insulate electrically conductive material in the bore of the magnet from the patient using blankets or sheets.

Considering that we're constantly bathed in them, this does raise the debate of adverse heath effects of electromagnetic fields.
posted by cenoxo at 7:58 PM on August 21, 2005

Well, we're constantly bathed in electrical fields, too. Nonetheless, a lightening strike can still ruin one's day.

Are there any groovy, laymen-interpretable images from an MRI? 'cause if there are, I'll be sure to jump on the chance to take part. Otherwise, I think I'll reserve it to a doctor's recommendation.
posted by five fresh fish at 8:10 PM on August 21, 2005

Here's a link to a couple of groovy yet clinical MRI images of sexual intercourse and female orgasm. Safe for work.
posted by JDC8 at 3:04 AM on August 22, 2005

casarkos writes "the techs themselves often walk around with a big bunch of keys around their necks"

To be fair keys are usually made of brass and therefor are safe to have around a MRI. The key ring on the other hand ...
posted by Mitheral at 11:54 AM on August 22, 2005

polyglot writes; Kirth Gerson: it usually vents to the outside atmosphere.

Damn safety equipment takes all the fun out of things.
posted by Kirth Gerson at 5:52 PM on August 22, 2005