Every rad resident must take the physics board exam to become board certified. This test includes the fundamental physics of all of the imaging modalities used by radiologists. This includes, X-rays, CT, MRI, utrasound, nuclear medicine, radiation safety, and radiobiology. Thus we have background knowledge of what is taking place in all of the images we interpret and can have the techs adjust parameters to get a better image. If you've ever seen radiation burns from a cardiac cath patient, you'll understand why this is essential knowledge (which many cardiologists seem to lack).