Also interesting to know that someone can go through 104 MRI per year safely.
The radio waves generated for the technique can cause heating when the energy is absorbed. This should be limited by how the MRI is designed, however I am not familiar with the detailed design of MRI instruments.
More research could be done in this area for very long term effects, but I haven't seen any convincing evidence for concern.
ex: http://www.sciencedirect.com/science/article/pii/S0009912011...
PS: Ands yes I mean MRI not CT.
There are high field research magnets, but most of the stuff over 7T are small animal magnets anyway (it is very much easier to maintain homogeneity in the main field over a smaller bore. So you're well into "research only" territory here.
There are other trade offs with field strength also, so it really isn't a matter of just "bigger is better".
None of this is clinically relevant, and none of it is US specific.
To be fair, the SAR problems become bigger at bigger fields too, which is related to what you are talking about. It's not really sensible to talk about this as a "problem of bigger fields" because it is there for all systems, and furthermore is also pulse-sequence dependent. By which I mean you may have a pulse sequence that is fine at 3T but woudl be dangerous at 7T, or 7T -> 10T or whatever.