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.