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Nano-coating To Make Implants MRI Safe
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."
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.
"Black holes are where God divided by zero." - Steve Wright
So when will they make them edible?
Eh? It's MRI? Darn.
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Like... dental fillings?
Does anyone know what makes some metal implants worse than others? Is it just a question of size?
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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?).
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.
:), 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.
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
(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.)
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.
Please help metamoderate.
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.
Could you coat, say, a gun with that stuff and make it invisible to metal detectors?
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Could this technology also be used to shield RF-sensitive circuits, or perhaps EMP-harden ICs?
-boredman
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 reflecting and absorbing all the radio.
If you use a copper sheath, for example, you have an *excellent* conductor; it means it will absorb the RF, convert it into electricity, and then that electricity, being essentially an inductive short, will heat up as more energy is pumped into it, and then get dumped back into the body as heat.
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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.
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!
.. 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 is inadvertantly presumed safe, as by my very diligent coworker who took in an IV pole that looked just like ours (there are expensive aluminum equivalents to these items) -- the pole was aluminum, but not the base. Perhaps a walk-in patient doesn't tell when interviewed about the Zippo lighter in her pocket which then almost smacks into the tech's (my) head.
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
The room seems no different from anywhere else, and the magnetic field increase exponentially as you approach, easily ripping something away before you can react.
A prudent solution is an airport-style metal detector. There are practical problems with using them that i don't recall; some places do use them. The wands work, but leave you vulnerable to the vacant-brain syndromes above.
As for the Westchester oxygen bottle, I believe what happened was that a magnetic-safe gurney was used but the ordinary oxygen bottle was concealed n the tray beneath by the sheet. This does not justify the tragedy, but demystifies it some. We always followed accidents with great interest.
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.
Those who sacrifice security to condemn liberty deserve to repeat history or something. - Benjamin Santayana
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.
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