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Science

Nano-coating To Make Implants MRI Safe 56

Posted by Hemos from the advancing-the-field dept.
Makarand writes "Patients who have implants containing any kind of metal cannot be MRI scanned as the powerful electromagnetic radio waves can induce currents large enough to heat the metal in implants to over 70 C and damage surrounding tissue. Now, Biophan, a biomedical devices company, has developed a nano-coating material that can protect implants by preventing most of the radio waves from reaching the internal components of the implant by reflecting them. It's high electrical resistance also prevents currents from flowing around the implant's surface and heating any nearby body tissue. Biophan's coating is a mixture of poorly conducting nanoparticles held in an insulating matrix. The coating is a mere three micrometres thick and can cut the energy induced in an implant by 89 per cent."
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Nano-coating To Make Implants MRI Safe More

Nano-coating To Make Implants MRI Safe

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  • She was a great insulator, but she did make a heap of heat. I dunno which I prefered though.

  • Wow (Score:3, Interesting)

    by Gangis ( 310282 ) * on Monday June 02, 2003 @07:26AM (#6094467) Journal
    I had a cochlear implant put in 4 years ago and I kind of wish we had that technology for it then... It kind of sucks not being able to use some diagnostic tools. When I first got my implant, I was given a card that specifically excludes me from getting a MRI with a strength of one tesla or more and that if I needed one, I would have to have the magnetic portion taken out surgically.
    • I doubt this technology would have helped you. Your cochlear implant probably uses a magnet to hold the external transmitting coil (which also contanis a magnet) against your head. This new technology reduces the ohmic heating susceptibility in metal implants induced by the RF excitation pulse in the MRI by using some special coating but does nothing to mitigate magnetic field effects. Your implant will always be vulnerable to very strong (>1 Tesla I guess)external magnetic fields ripping it out (OW!)
  • So when will they make them edible?

    Eh? It's MRI? Darn.

  • Metal implants? (Score:3, Insightful)

    by cperciva ( 102828 ) on Monday June 02, 2003 @08:07AM (#6094621) Homepage
    Like... dental fillings?

    Does anyone know what makes some metal implants worse than others? Is it just a question of size?
    • An MRI is a really, really big magnet.

      -Sean

    • Re:Metal implants? (Score:3, Informative)

      by Noren ( 605012 )
      Whether a substance is ferromagnetic or diamagnetic is the big difference. To somewhat oversimplify, Ferromagnetic substances have unpaired electrons which become attracted to magnetic fields. Most common substances are diamagnetic- all of their electrons paired up- and are thus (very weakly) repelled.

      Many, but far from all, metals are ferromagnetic. Amalgams (compounds with mercury) in dental fillings are generally diamagnetic.

      A given metal atom may pair up its electrons and become diamagnetic if it

      • Re:Metal implants? (Score:3, Interesting)

        by Muhammar ( 659468 )
        I heard of a story about a worker who got into an MRS head scan. He started screaming and they pulled him out but it was too late - a steel splinter that was embeded in one of his eyes from a work-related injury and got undetected for years started moving around in the >15 Gauss magnetic field.

        [Scrambled eyes, anyone?]
        • ">15 Gauss"? You probably mean 1.5 Tesla, or 15000 Gauss. Refrigerator magnets have field strengths of several hundred Gauss.

        • ... a steel splinter that was embeded in one of his eyes ...
          That's why you should get a head X-Ray before you get an MRI (at least your first one).
          When I got an MRI, the doctor recommended that I get an X-Ray because I occasionally use a grinder to sharpen my lawnmower blade, but it's always a good idea to get one no matter what, at least for your first MRI.
          It's inexpensive insurance against a possible cause of blindness.

  • I'm almost thinking it's a hose... (Score:4, Insightful)

    by JCMay ( 158033 ) <JeffMayNO@SPAMearthlink.net> on Monday June 02, 2003 @08:16AM (#6094686) Homepage
    This has got to be a hose; a material can't be a "good reflector" and an insulator at the same time.

    Mr. Maxwell taught us that EM waves are reflected from conductors because any electric field that is tangential to a conductor causes charges to move to cancel out that field (thre can be no electric field inside a conductor). These moving charges are more commonly called "currents."

    Insulating materials do not stop radiating fields; your radio works inside your wood framed house, doesn't it? Light propagates through the glass front of your CRT from the phosphors on the inside of the tube, doesn't it?

    Seems to me that if they're worried about induced eddy current heating of the implants, would it not make more sense to use *better* conductors, not worse ones? Better conductors would have lower I-squared-R losses, resulting in less resistive heating. Take that implant, put a few micro-inches of copper on it, and then seal it up with something biologically intert (some plastic?).

    • Re:I'm almost thinking it's a hose... (Score:4, Informative)

      by esonik ( 222874 ) on Monday June 02, 2003 @12:51PM (#6096775)
      I think you missed the part about "conductive nanoparticles that are implanted in the non-conducting matrix". As you might know from transformator theory, you can reduce eddy current loss in the yoke by making the yoke from a stack of thin metal sheets rather than a solid yoke, i.e. reducing the size of continuous metal parts.
    • I did some searching and I think I found a patent [uspto.gov] for this. From a quick read, it looks like the nano-coating is only for blocking magnetic fields. The Biophan's website talks about "Carbon-composite coatings". These might be for RF shielding.

      The website is pretty weak on details and the New Scientist article doesn't make sence.

    • Well, you are reasoning along the right lines, but your conclusions are incorrect. Isulators can be trasparent to some electromagnetic (EM) waves, but not nessesarily to the entire spectrum. That is, materials are trasparent to some frequencies but opaque to others. To demonstrate this point, lets look at the exaples you listed...

      Yes, the radio works in your house. This is becuase most of the materials in your house are transparent to radio waves (and those that are opaque to radio waves are too small
    • They said *electrical* insulator. So they aren't supposed to stop radiating fields, that's what the metal/semiconductor particles are for. The insulator is supposed to stop heat/current from building up by preventing a current from ever flowing through/around the device.

      So what they are describing is a very poor Faraday cage embedded inside a non conducting matrix.

      Like rebar inside a concrete building!

      Notice how you get no cell phone reception inside? The building is acting like a Faraday cage by reflect
    • The insulating materials in my house do a great job of stopping EM fields around 600 Terahertz.

      The sheet of white paper on my desk is a good EM reflector throughout the visible spectrum, but doesn't conduct worth a damn. I can shine a 5 Watt green laser on it and it doesn't even heat up noticeably.

  • Wolverine didn't fry in X-Men???

    • Re:so how come... (Score:1, Offtopic)

      by Bonker ( 243350 )
      While the above is funny, it's important to remember that movie and comic book physics are nothing like real-world physics.

      Like many fantasy characters, Wolverine casually violates the laws of physics and biology. Compare Logan to the cyclopses and giants of mythology, which were almost certainly based on deformed or diseased humans. Most descriptions of giants have them towering above humans. Since volume (and therefore mass of similar density material) increases with the cube of radius, most fantasy gian
      • Giants can be explained by the annunaki [google.com], a race of space gods that mingled with the earthly population. Their presence is even noted in the bible, which speaks of gods walking amoungst men. Unfortunately, however, the bible holds little more credibility than the average comic book... ;-)

  • Magnetic field? (Score:5, Informative)

    by MacAndrew ( 463832 ) on Monday June 02, 2003 @08:47AM (#6094854) Homepage
    I was an MRI tech for 4 years, so golly I have special experience here. Our primary reason for restricting metal was not heating -- the RF is not all that strong, not like a microwave -- but the 1.5 Tesla magnetic field (that's a moderately strong magnet). Our concern was that the field would pull or twist something sensitive like an aneurysm clip. Also the metal would cause a distortion in the magnetic field such that it was impossible to extract images near something fixed, such as screwed into bone -- the biggest practical problem here.

    The field is *powerful* -- in one case it took several of us to pull free a chunk of metal another tech had unwittingly brought into the room.

    I can see how this would be useful for non-magnetic materials like most stainless (yes, there are magnetic blends of ss in the 4xx series before someone tries to correct me :), which would be susceptible to induced current. We were mostly worried about older pacemakers that were not entirely solid-state. Many pacemakers are not full-time, btw, that it the heart can work without them.

    (Rudimentary MRI primer: the primary field sets up a net alignment of molecules in the body, most significantly water; the RF pulses then tweak these molecules so they emit RF of their own, revealing location and quantity. Things have evolved since i was a tech, however.)
    • Heating and burning are well-known concerns. A small sample of the peer-reviewed literature turned up by a quick Medline search includes:
      • Thanks for the cites. However as a veteran of administering many thousands of scans and having talked with our Boston regional service techs about other magnets, I'm skeptical of "numerous" burns -- these incidents are thankfully rare and usually involve the poorly thought-out introduction of foreign objects, not medical implants and the like addressed by this invention. Our EKG monitoring cables were of ordinary design but constructed to be compatible with the scanner. With third-party devices or improp
        • Burns from MRI scans are rare, but entirely possible, especially with patients connected to monitoring equipment. The important thing when dealing with wired patients is to make sure none of the wires or leads form any kind of loop. Otherwise you end up with a classic implementation of Maxwell's laws and induce currents and heating in the looped lead, resulting in a burn potential.

          This happened recently in the hospital I work at, and while the patient wasn't seriously injured, it did cause a bit of a sti
        • I won't quibble with your experience. I would only point out that since so many MRIs are performed, burns can be both numerous (raw count) and rare (small fraction of total scans performed).

          If the burn rate were 0.001% (This number is just pulled out of my hat to illustrate. I have no reason to believe that it has any relation to the actual frequency of burns), any given clinic could expect to perform tens of thousands of scans without seeing a single burn, but given 40 million scans [amersham.com] performed each year th

          • Point taken! I guess the difference is psychological. As someone who had to talk all those *psychaitric* patients through a claustrophobic 40-minute exam that required no motion, their confidence was crucial, so I sure would pick rare over numerous to depict risk. If I were looking at scanner or equipment design or training the latter -- well, no, maybe "significant." Actually a 0.0001% rate would be pretty damn good.

            This idea, to try to make scans available for more people, certainly benefits that sub
            • I sure would pick rare over numerous to depict risk.

              Damn straight! You are correct to do so. The total number is completely irrelevant to an individual considering an exam. The right number is the probability, which you correctly focus on. The problem you're dealing with is that the patient is likely to read about a rare adverse event in the newspaper and focus on that, just as with shark attacks at beaches.

              In contrast, according to the Institute of Medicine [nap.edu], any time you check into a hospital in the Un

    • I was an MRI tech for 4 years, so golly I have special experience here.

      I'm just curious, what are the benefits of MRI vs PET or PET vs MRI? Would metal inside someone conduct positrons with a PET scanner?
      • I never worked with PET, though some researchers there were correlating MRI's fabulous depiction of structure with PET's spatially blurry depiction of metabolism (someone was doing SPECT, too). I speculate metal would not be a big problem with PET, depending on its quantity, though it would of course tend to absorb radiation (PET actually detects the radiation resulting from the annihilation of the positron). MRI has expanded since i did it to fMRI, or functional MRI, which does show metabolism and doesn'

  • pulled out (Score:4, Interesting)

    by SuperBanana ( 662181 ) on Monday June 02, 2003 @09:57AM (#6095346)
    Patients who have implants containing any kind of metal cannot be MRI scanned as the powerful electromagnetic radio waves can induce currents large enough to heat the metal in implants to over 70 C and damage surrounding tissue.

    That's not the only problem- there's the whole magnetic force issue. Remember the last Bond movie, where he's in the MRI room? It's not an exaggeration- anything ferrous within a 20+ foot radius will, in fact, get picked up and pulled toward the center of the machine. That's why, unlike the Bond movies, nothing ferrous is ever supposed to be allowed into the same room.

    A child at Westchester Medical Center was killed a year or two back when an oxygen cylinder against a wall was launched into the center of the MRI machine(it literally flew through the air into the center), crushing his skull.

    Another "famous" incident involved a prison inmate who was not killed or injured, but the policeman guarding him lost his gun- I can't remember if it was holstered or in his hands, but it ended up hitting the MRI machine, AND discharging- not to mention I think it also partially damaged the dewar vessel surrounding the magnet. In both cases, the nurses and doctors hadn't managed to think through the most basic safety issue- NOTHING metal goes in an MRI room, PERIOD(Westchester never did publicly "figure out" how the oxygen cylinder, which never should have been in there in the first place, got there- much less why the nurses didn't remove it.)

    Now, imagine if the metal object was inside your knee...forget "damaged tissue", you could end up with a face-knee transplant.

    • "Nothing ferrous is ever supposed to be allowed into the same room."

      So really hairy men can't get MRIs either?
    • Aren't most metal implants made of Titanium (non-ferrous) anyway (for bio-compatibility) ?
      • Total joints (i.e. total hip and knee replacements) have surfaces which are usually made of some type of steel - the Titanium doesn't have good wear characteristics in the body for total joints. Titanium forms a surface oxide coating which leads to pitting, increased poly wear and further "rusting" of the titanium. Thus most total joints have stainless steel for the plastic metal interface. Steel has been used in the body for years w/o any problems. Titanium has become more popular in the last decade or
    • Interesting...I have some MRI films here in my office showing a metal screw and staple in my knee. The films were taken to examine a re-injury of an ACL reconstruction (which fortunately turned out not to be another tear). I can't find the original surgical report, but I was under the impression that they were made of surgical steel. They didn't rip out when the second MRI was taken.
      • Most screw anchors are Titanium - a non magnetic metal. Titanium is also "good" in a MRI cause it doesn't degrade the signal much - unlike steel which causes all sorts of artifacts - making the MRI useless in that area being scanned.

    • MRI accidents (Score:3, Informative)

      by MacAndrew ( 463832 )
      Believe me, anyone who works with MRI is aware of the risk! We wouldn't even keep things in our pockets, including easily erased bank cards!

      But accidents happen. Perhaps you have someone unfamiliar visiting like that cop (I bet he just walked into the room before they had a chance to demetal him .. I once scanned a prisoner in full shackles because the two rather large police escorts said he was too dangerous to remove them ... but they were attached, hence not a problem). Perhaps a piece of equipment i

  • PSA (Score:4, Funny)

    by Henry V .009 ( 518000 ) on Monday June 02, 2003 @10:14AM (#6095463) Journal
    Never, never, never, carry scissors into the MRI room.

    The best thing about this technology, of course, is that we will be able to wear pace-makers into the qwikee-mart again.
    • > Never, never, never, carry scissors into the MRI room.

      Isn't it,

      Never, never, never, run with scissors in the MRI room?
    • The best thing about this technology, of course, is that we will be able to wear pace-makers into the qwikee-mart again.

      Well, hot diggity shucky-dang! Nothin' thrills me more than grabbin' a pacemaker, slappin' it in and firin' it up, and headin' down to the ol' Qwikee-Mart!

    • Re:PSA (Score:2)

      by Imabug ( 2259 )
      it's never wise to bypass the metal detectors even if you don't think the object is ferro or diamagnetic.

      http://radinfo.musc.edu/images/photos/MRIvsChai r 01 .jpg
      http://radinfo.musc.edu/images/photos/MRIvsC hair02 .jpg

      This happened to our brand new 3T magnet. A nurse attending a patient decided to pull a chair into the room so she could sit down. There were already wooden chairs in the room, but for some reason the person decided this chair would be better.

      The magnet was down for about 3 days while serv

  • hmm... (Score:2, Interesting)

    by EMH_Mark3 ( 305983 )
    Could you coat, say, a gun with that stuff and make it invisible to metal detectors?
    • I was thinking more along the lines of coating electronic housings with that. Help reduce em from devices interferring with each other....
      On the gun issue you could probaly make the outside coating thicker and use a barrel plug of the same stuff to keep any fields going down the barrel. Course you would have to make sure that when you coat the gun you dont leave any cracks for the field to get into.

    • Re:hmm... (Score:2, Informative)

      by oobar ( 600154 )
      It would have no effect on metal detectors. The metal detectors work by sensing the rather distinct change in magnetic permeability of the space near the coil that occurs when something containing ferromagnetic elements (iron, nickel, cobalt) is present.

      By the way, did anyone else think that guy mentioned in the article who died because he failed to mention his pacemaker (even when asked several times) should be nominated for a Darwin award?
  • Don't bother RTFA. There's only one more paragraph than the post, and only one thing not mentioned there. Of all the days to decide to click the link....

  • Other shielding possibilities? (Score:3, Interesting)

    by boredman ( 169127 ) on Monday June 02, 2003 @01:51PM (#6097382)
    Could this technology also be used to shield RF-sensitive circuits, or perhaps EMP-harden ICs?

    -boredman

  • not a nano coating (Score:3, Insightful)

    by Goldsmith ( 561202 ) on Monday June 02, 2003 @09:55PM (#6102107)
    The coating is a mere three micrometres thick

    I guess that would make it a microcoating?

    We have a usefull word for nanoparticles as well... molecules.

  • High School Field Trip (Score:3, Interesting)

    by jasno ( 124830 ) on Tuesday June 03, 2003 @09:08PM (#6111069) Journal
    I remeber going on a high school field trip to the University of Washington to check out their MRI equipment. It was part of my occupational electronics course, and our Prof. was an ex-GE medical guy with connections(excellent Professor, too). I had prepared a coil of 10ga copper wire(maybe 8" across, 3/4" thick bundle of wire, don't remember how many windings) with a flashlight bulb attached. I also brought an audio cassette tape and an aluminum vent filter(12"x24"x1/4" or so).

    I tried moving the coil of wire in the opening of the MRI and didn't see anything on the bulb, so I removed it and shorted the wires together. When I placed the loop near the opening and attempted to twist it, it resisted with something like 10 ft/lbs of torqe. It was incredibly eerie having something floating in midair resist so strongly. The audio tape was almost ripped out of my hand and had the bias stripped off so it was no longer usable. When we stood the aluminum filter on its end on the patient bed and let it fall, it fell like it was submerged in a viscous liquid.

    They told us that a monkey wrench takes 3 guys to pull it out and if you walk into the room with steel toed boots you can feel your legs getting pulled to the side. Very cool stuff.

  • Current MRI magnets operate at about 1 Tesla, with a bore large enough to accomdate a human head, or even a whole human body. In the future, there is a good chance that we will be using more powerful magnets, which may exacerbate the effect this company is trying to compensate for. The question is, will the thickness of their coating suffice when we are using higher power magnets? For instance, at the Ohio State University Medical Center, the world's most powerful medical MRI unit is in the first stages

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