The Clemson Bioengineering department normally wants PhD students to come up with a proposal and do the qualifying exam within 18 months of starting. Since my plan is to do course work and research concurrently, I need to come up with something sooner than that.
I've been rolling around a few possible areas in my head and doing some literature searching to see what's been done.
One obvious area, given our brand-new-state-of-the-art-only-3-in-the-US dual source CT scanner, is dual energy CT. There's been some work doing tissue discrimination and characterization using dual energy CT, but not too much. I could also spend some time studying some of the dosimetry characteristics of doing dual energy CT.
Another area that I would like to explore is phase contrast imaging, although that generally requires a synchrotron source and fairly specialized detectors. Plus I'm not sure that would fit in with the Bioengineering group very well.
There's another idea about CT dosimetry that has been rolling around in my brain for quite a while now, but it's going to take a fair bit of work to flesh out properly and see how feasible it is. If I can take this concept, formalize it, test its validity and make it easy to implement, it could potentially change the way patient radiation doses are determined by the CT scanner.
That would be a lot to do for a PhD, but even if I only accomplished half of it, it would be a big thing.