Medical x-ray imaging systems must be designed to ensure that maximum image quality is obtained for a specified radiation dose to the patient, and quality assurance programs are used to ensure these standards are maintained. This course is designed for anyone who wants to extend their understanding of how image quality is related to detector design and what that implies: how to talk about it, how to think about it, how to measure it and how to compare it. Performance metrics including the MTF, NPS, NEQ and DQE in digital radiography and mammography will be discussed. A cascaded-systems analysis will be used to help interpret the DQE of some real systems. The DQE of photon-counting systems, and the impact of detector limitations, will be discussed. Both non-mathematical intuitive descriptions and more rigorous mathematical descriptions will be presented.