I'm very much interested in brain imaging as it relates to psychiatry and I believe there are no brain imaging fellowships open to applications from psych grads. Are there any opportunities out there for psychiatry residents or grads to further specialize in brain imaging?
This is what I would do:
1) contact departments(radiology, neuroradiology, neurology,etc) that can offer to teach you what you want at your university. Be ready to explain your unique situation, future goals, and what you want to learn
2) talk to your PD about the opportunity that you were able to set up with with whatever department(i.e. Radiology); get ure PD's blessing; you'd be surprised how open other departments are
3) if you manage to get this far, bust your butt and shine like crazy when your there for that half day, or month or whatever
4) get to know people in that department
5) ask for a letter of recommendation and ask if they have any suggestions as to where you can apply or where they went for their brain imaging fellowship
6) apply with your unique background
Just be aware, this doesn't come easy and requires tons of emailing, answering why you want to do this, coordinating everything yourself. And yea, it may not give you the ABMS certification, but doing the fellowship will give you the privileges at hospitals in the future down the line. Applications are always open, you just have to prove that you can put in the work, have the knowledge to be in the fellowship, and show that you have been able to work in that area. Good luck!