Image quality and patient exposure in mammography, tomography, angiography and bone radiography

In diagnostic radiology, the physical factors affecting image quality and patient exposure are complex and must be studied for each individual procedure. They are a function of recording system unsharpness, geometric unsharpness, image noise, and of the shape, size, and absorption properties of the anatomic part radiographed and the lesion to be detected. The choice of recording system has a significant effect on image quality, and the speed of the recording system is directly related to patient exposure for each procedure. This paper discusses the complexities involved in the selection of recording systems for four radiologic procedures. The authors describe in detail their most recent work on mammography with the Lo-Dose system, whereby a significant reduction in exposure may not reduce, but may even increase, the diagnostic accuracy by reducing geometric unsharpness. We also describe several examples: (a) in tomography, image resolution is not decreased and diagnostic certainty is affected by a change from a medium-speed screen to a high-speed screen recording system (patient exposure is reduced by a factor of 2); (b) in fine-detail skeletal radiography, the diagnostic information is increased significantly by a change from a conventional screen-film technique to a non-screen technique with fine-grain film and optical magnification, but at the cost of increased patient exposure; and (c) in cerebral angiography, diagnostic information can be increased by use of a screen-film recording system of higher resolution, but lower speed for imaging of small blood vessels. Modulation transfer functions and clinical examples are used to illustrate each procedure. (author)