Hi all,
I’m planning on implanting an x series product in the near future and wonder if they are safe up to the new Texas MRI standard which is close to 18 teslas. I’d really hate to have to remove it after implanting it.
Do you have access to an MRI with a field strength of 18T, or are you just curious? I’m sure if you’re willing to test it out, Amal would send you a loose tag to hold near it and see what happens.
2 Likes
Unfortunately no, I only posted because I heard from a friend that 18T was the new standard here. While I do have another friend who is a radiologist, their machine is 4-5 T.
Well I guess we can only conjecture for now. Here is the Dangerous Things info on MRI
The unit Tesla is used to communicate magnetic flux density. As far as I can tell from the math, the unit Tesla scales linearly. That means a 3T MRI has a maximum field strength that will produce twice as much pull on the implant as a 1.5T MRI, and a 18T MRI will produce six times as much pull on the implant as a 3T MRI.
One important note is “maximum field strength”. Magnetic fields drop off very quickly with distance (inverse cubed.) The MRI is directing the maximum field strength at the region to be imaged. If the implant is in your hand which is a foot or more away, the implant may not be experiencing the full strength of the field (I’m not an MRI tech, so don’t quote me.) Hospitals can also provide mu metal shielding plates to put over your hand that will bend the magnetic field around it.
Another thing I would like to clarify is that the flex implants are unlikely to be affected by an MRI at all. The copper coils are not magnetic, and the amount of ferromagnetic material in the chips is negligible. The only reason the x series are a concern is because their antenna is wrapped around a cylinder of iron.
1 Like
Interesting note about the Flexes - didn’t know that. Just for curiosity’s sake, does the MRI induce any kind of current in the Flex coil? And could it possibly be damaged if enough current got induced into the coil?
@bepiswriter I’m not sure 100% on this, but I don’t think that the field from an MRI could overload a flex. Something about frequencies not being in the same band. @amal Did you get any force data from the 3T test, that would save me the math of creating a model from scratch to simulate the forces.
My understanding of this process is not complete (I’m not an RF engineer) but I’ll try and convey the salient points.
We talk about coupling often on these forums. The quality of the coupling between two coils has to do with many factors, but two of the most important are the shape of the magnetic field produced, and the flux density in that field. When those two factors match well, two coils will have good coupling and in our use case they can be read and written to reliably.
The reason “coupling” is all we worry about is because all the equipment we use is “tuned” to specific frequencies (say 13.56MHz). That’s why you can’t communicate with a 125kHz tag using your phone. All the waves that hit the antenna at a different frequency than the one the circuit is configured to receive get filtered out (attenuated). They’re present in the tag, their strength (and therefore current induced) is just greatly reduced.
MRIs need to vibrate cells in a very particular way (Larmor frequency) to get useful information from the scan. The frequency that they operate at is dependant on the field strength. Here’s a handy chart I found:
So we might need to worry about overcurrent frying the chip when it’s a 0.3T MRI. That would depend entirely on the type of chip and the protection built into the die.
1 Like
That chart was what I was most curious about - the frequency of each strength. Theoretically there shouldn’t be too much of an issue, although it’d be ironic if the lowest strength MRI killed a chip.
1 Like
Ha, yeah. I suspect that would be good news if it meant the technology was being phased out in favor of more powerful units. Sorry if I was blasting you with a bunch of information you already knew, I figure somebody can get some use out of it.
Nah you’re good, I’d always rather have more info than less.
Just FYI I’ve had an MRI done with a flexDF in my hand. No issues at all, still works perfectly.
!!! uhh… are you sure it’s not 1.8T? Because the only MRIs I’ve seen with T over 7 are in uni labs and special research facilities. The only thing I could find online about an 18T MRI machine was this article from May 2019 that talked about developing the “world’s first 18T MRI machine” with an 11cm bore… so something tells me he might have meant 1.8T
Actually the problem has to do with the resonance and collapsing field. Any conductor can become an electromagnet in a field event. That’s the problem, not just the ferrite core of the x-series. Positioned correctly, a simple piece of copper wire could generate it’s own electromagnetic field from the lines of flux running through it (eddy currents) and produce physical effects such as heating and kinetic motion. In essence, this is what’s happening with the magnet-down-the-copper-pipe trick. It’s called the Lenz’s Law… and here are two of my favorite vids about it… the latter of which actually explores MRI tricks 
1 Like
Not sure, I’ll talk to him again this week. At this point, my implant is ordered and I’m committed. So if it get pulled out for any reason, screw it. Also I called sparrows tattoo in Mansfield/Arlington Texas to see about having a professional install it, but they straight up told me it’s illegal for a piercing artist to do that here, so I guess I’ll be doing the procedure myself.
If you want to drive to Dallas or Austin, Pineapple is a great dude who will do a good job; https://www.shamanmodifications.com/piercing-by-pineapple.html
My car is so close to death, so I don’t think that’s an option unfortunately. It can’t be that hard to do myself, I’ve got medical training.