Medical imaging has become a powerful non-invasive diagnostic tool for the modern medicine. It has an interdisciplinary achievement of many physicists, chemists, engineers and medical doctors, especially in the last twenty-five years. In this introductory, three-unit course, we are going to discuss the underlined physics, imaging techniques, imaging system and their applications for systems used in diagnostic radiology. For medical imaging that is not used in radiology, we are not able to cover it at this point due to the limited time we have in one semester.