Concerning the photomultiplier tube problem, the two solutions are optical coupling and avalanche photodiodes. In optical coupling, the electromagnetic radiation is detected within the magnet and coupled optically to the PMT’s outside the magnet. Avalanche photodiodes are silicon devices that simulate the cascade effect of PMT’s but are virtually unaffected by high magnetic fields.

Also, I saw that you mentioned that ISMRM had very few talks on MRI/PET last year. Unfortunately, it looks to be the same this year. However, you should check out SNM this year. Most of the interest in MRI/PET systems will be there.

note – I mistyped CT above when I should have typed PET/CT (now fixed). I see the overall point; PET/CT is a success because it marries anatomy (CT) with function (PET). MRI/PET would do the same, but offer functional imaging on both sides of the fence, and bring superior soft tissue contrast to the anatomic side. I agree Dustin that the attenuation issue is probably the single biggest obstacle (though one wonders, if PET/CT systems are the default nowadays anyway, why not merge MRI with PET/CT rather than just PET.. MRI/PET/CT!)

I think that PET is sexy but in the long term is too specialized. The economics of 18F dont lend themselves to flexible clinical imaging the way that SPECT can. The more I think about it, the more I believe that an MRI/SPECT combo would be way more useful overall.

Can MR/CT replace PET? Thats an interesting question. Do we even need CT to replace PET? What does CT really bring to the, er, table? Unless you mean, MRI/CT could replace PET/CT. But then if you’re gonna go through the ttrouble of integrating CT anyway, why not go for the trifecta system again

PET/MR just can’t replace CT. CT wins by so much on speed/resolution/geometric accuracy that it’s not even funny. Also, there isn’t a way to easily correct for attenuation in MR/PET like there is in PET/CT.

For that matter, if you have certain implants you can’t even walk into an MR suite.

Now MR/CT could technically replace PET, simply because MR can detect 19F, which a lot easier to get than 18F. The sensitivity might even be as good or better. This would require some major improvements with whole-body MR technology first, though.