RELATIONSHIP BETWEEN DETECTABILITY BY THE 18-AFC METHOD AND SPECTRAL SN RATIO

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  • 18 肢強制選択法の検出率とスペクトル SN 比との相関について

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We examined the relationship between SN ratio of visual threshold value and radiographic image by using various sizes of plastic columns and various speeds of screen/film systems to change the signal value. We tried to get a visual estimation applyjng the 18-AFC (18-alternative forced choice) method using five radiological technologists. On the other side, we got a physical estimation applying the spectral SN ratio composed of NEQ (u) (Number of noise-equivalent quanta (u)) and distributed spectral of the signal. As a result, when we assumed the threshold value of detectability of the 18-AFC method was 50%, we found that SN ratio of the visual threshold value was 3.23. When the speed of the screen/film system increases, the threshold value of the SN ratio decreases. We were able to confirm that the visual characteristics depend on the contrast and spatial frequency of the signal.

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