Do you mean radiology, as in you're an MD and moving into a radiology residency? Or are you taking an x-ray technician course? Or are you a medical physics graduate student with focus on imaging?
If your intention is to become a medical physicist, you will want to have a solid foundation in calculus and differential equations. The most applicable math course I took was a "mathematical methods for physicists" course that covered Fourier transforms and the principle of convolution and such, which are using in the theory of image processing.
On the medical side of things, you don't usually need to go quite so far in depth, but holding a good grasp of matrix operations will certainly help. Regardless of the program, make sure you satisfy the prerequisits.