Generally speaking, image quality is proportional to radiation dose in computed tomography; this is not the case for plain film radiographs where image quality can be obstructed by radiation dose. It is extremely important to track images based on their diagnostic value when preceding with any dose optimization program. For an in-depth discussion of the relationship between image quality and radiation dose see: McNitt-Gray, M 2002:  AAPM/RSNA Physics Tutorial for Residents: Topics in CT