Method of measuring contrast‐to‐noise ratio ( CNR ) in nonuniform image area in digital radiography

Summary One of the physical indices for evaluating the image quality of digital radiography is the contrast‐to‐noise ratio ( CNR ). The CNR was reported to simulate human perception. Thus, the CNR is a variable index for evaluating detectability in digital radiography. However, it is difficult to evaluate the CNR in a nonuniform image area. In this study, we have devised a new method for measuring the CNR in a nonuniform image area on digital radiography using the top‐hat transform. Furthermore, we investigated the radiation dose dependence of CNR in the digital image of an anthropomorphic breast phantom containing a simulated calcification. We have shown that the CNR in a nonuniform image area can be analyzed with high accuracy by the devised method for measuring the CNR . As for the radiation dose dependence of the CNR , the CNR increased with the mAs values and fell depending on the increase in the density of mammary glands in the anthropomorphic breast phantom. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(7): 32–41, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/ecj.11416