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."

Comments

Wow

[Gangis]

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'm almost thinking it's a hose...

[JCMay]

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...

[esonik]

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.

Magnetic field?

[MacAndrew]

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.)

pulled out

[SuperBanana]

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.

PSA

[Henry V .009]

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.

Other shielding possibilities?

[boredman]

Could this technology also be used to shield RF-sensitive circuits, or perhaps EMP-harden ICs?

-boredman