Investigation of modulation transfer function (MTF) in a digital imaging system

The modulation transfer function (MTF) has been used for evaluation of radiographic image quality. However, in digital radiographic system such as a computed radiography (CR), the MTF can not be used in the same way of an analog system of evaluation because digital system is not shift-invaliant system. Then, we suggest the 'MTFfinal' which includes geometric unsharpness, detector unsharpness, unsharpness of the sampling aperture and unsharpness of the display (Laser-printer). It is an analog component in the digital system and in agreement with the definition of the MTF. Furthermore, an overall aliasing has to be used with MTFfinal for evaluating the digital system because it is one of the important factors of the digital system. The MTFfinal and the overall aliasing can be obtained from the overall MTFs of the center alignment and the shifted alignment. (author)