Barry Ng
Wed. 10 Jul.13,
17:10
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I am trying to understand why titanium is considered "MRI Safe".
I see three potential problems when considering the MRI safety of a material:
1 - If it is a ferromagnetic material extreme damaging forces will be applied to the material if exposed to a very strong magnetic field. Titanium is not a magnetic material so I do not see this as a problem.
2 - When a relatively large flat conductor (e.g. a titanium plate) is exposed to a changing magnetic field (Faraday's law) eddy currents will be created internally as the result of induced voltages. These eddy currents can be very high and cause resistive heating ("I squared R losses"). I would think these eddy currents would have the potential to cause extreme heating of the titanium. I know from experience this does occur with steel and titanium has a conductivity about the same as steel. Titanium is not magnetic as is steel but induced voltages due not require a ferromagnetic material (.e.g. copper as used in real world generators, etc.).
3 - Induced voltages are created across the length of a conductor as the result of the conductor being exposed to a changing magnetic field ("genrator effect" - Faraday's Law). Again this effect does not require a magnetic material. So why, at best, does this effect not have the potential to be uncomfortable or even very painful to the MRI patient being exposed to a huge changing magnetic field?
Invariably the response to why titanium is safe focuses on the fact that it is not magnetic. I get the deer in the headlight look when I ask about eddy current heating and induced voltages.
Please help me understand why unduced eddy current heating and induce voltages are not a concern.
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