I'm a mathematics major, interested in dynamic systems modeling (if I met any of you in the interviews and you didn't make the connection yet, you probably know who I am now! 🙂 ). I too am not so interested in a wet lab necessarily.
Arguments can be made that UofWashington is the absolute best place to go for mathematical biology. They have ~20 faculty members studying in this niche area, far more than the next best (probably UMichigan, with about 8). A few of these guys are bioinformatics.
I really don't think that UofW is a powerhouse in medical imaging, though I'm not certain. I know that both Yale and WashU are very strong in this area, though I'm sure there are more.