I'm no radiologist or physicist but heres my take:
We have a 7T at the NIH and from what i've seen so far, it seems to be a mixed bag. Getting decent images apparently requires a lot more effort since the signal-to-noise ratio(SNR) is different for 7T as opposed to 1.5 and 3T.
There's a Dutch guy in the NIH's NMR center by the name of Jeff Duyhn who has been saying that there's a curve for the magnets in terms of SNR. That is, there's better SNR for moving from 1.5 to 3T, but the move from 3T to 7T only yields nominally more signal in comparison to the exponential increase in noise. Maybe there needs to be some better shimming and post-processing of 7T data? At the end of the day though, I get the feeling from the physicists that 3T is the sweet spot for SNR.
Everyone in the NMR center is moving towards multi-channel coils and faster image reconstruction platforms for the 3Ts. The current 8-channel coils that we have produces some impressive EPI images with a TR of 0.5 seconds! In fact, a lot of the 3Ts are going down in the next few months so that GE can make the upgrades for 16-channel head coils. I'm sure that there's probably a sweet spot for number of channels too, but I guess they'll figure out what that is as the multi-channel technology progresses.
As for 7T being harmful... I cant say that theres anything published linking harmful side effects. However, when I jumped into the 7T, I felt the room start to spin as if I had been spun on a chair for 30 seconds. After the dizziness passed though, I fell asleep like I always do in the scanners.
🙂
I'm told by others that the dizziness passes the more often you get scanned in the 7T but I have a feeling that 7T isnt going to make its way into a clinical setting for a while to come unless they can think of a way to prevent that room spinning dizziness.
Can private practices really afford to have 3T's nowadays? Wow, what a great time to be alive!
bosky said:
There is some debate about this question re: very high fields in the academic MRI community at the moment and I suspect we will be using 3T clinically for the next 5-10 years (especially in private practice). These higher fields will probably prove most beneficial to fMRI and MR spectroscopy research.
These magnets are extremely expensive, difficult to site, it takes 10-20 minutes to bring someone into the isocenter of the bore (due to dB/dt), and there aren't a lot of rf coils designed for these fields (none comercially available). Field strength doesn't seem harmful up to at least 10T, but the FDA has only approved 4T for clinical non-research applications. Further, T1 contrast disappears at high fields (diffusion is the future!). Recent research also demonstrated that rf waves at these field strengths form destructive interference patterns that leave huge signal voids in the middle of "large samples" (aka human head) that will require significant further coil development. You also can't currently use rapid imaging techniques at high fields - EPI is terrible! this means you lose time by resorting to PGSE sequences....
I think most companies realize these problems and are prepared to make the academics work it all out. Companies are more focused on building better gradients and rf coils to maximize the potential of 3 and 1.5T scanners.
Cool research toys though! I used high field magnets frequently for my PhD research and work in a lab that works on high field problems (I guess that's obvious from this email!), and I want to go somewhere with a 7T human scanner for my residency....
