Visual evaluation of X-ray image with C-D diagram is widely used as a QC method of imaging monitors in hospitals. The accuracy of the visual evaluation is theoretically improved by observing test samples of X-ray images over and over again. However, the repetition of the observation probably causes the observer's visual fatigue. Consequently, the accuracy may be down. In this paper, we propose new visual evaluation with C-D diagram made on the basis of decision expectation of X-ray imaging signals which is deduced from Markov chain. In a Markov process, decision probability of the signals in an X-ray image sample changes with the number of observation times and finally converges at a certain value. C-D diagram was made based on the decision expectation, which was calculated, from the signal strength and its convergence probability. The C-D diagram with Markov chain is in good accord with that obtained from 30 times observation. The result suggests that it is possible to reduce the observation times by using the Markov chain. Therefore, we propose that the C-D diagram with Markov chain is useful for visual evaluation of X-ray image.
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