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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 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.)
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.