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