Books on medical imaging
I quite like the Medical Imaging Signals and Systems by Jerry L. Prince and Jonathan Links. If you're looking for a DSP approach to medical imaging, this is a good start. It's also quite good on the physics of medical imaging. the format of the book follows one medical imaging modality at a time. It first teaches you the relevant physics of how the imaging itself works for that modality, and then goes into the signal processing side of things in the following chapter.