Relationship between pysical and visual image qualiy of asymmetric screen-film syatems

We investigated the relationship betwwn physical and visual image quality of asymmetric screen/film systems. The physical image quality parameters included the characteristic curve, modulation transfer functin (MTF), and noise Wiener spectrum. The visual image quality indiecs, such as sharpness and grainiess, were determined using a method of paired compari-sons of ahest phantom radiographs. When the speeds of asymmetric systems increased, the visual evaluation for sharpness was lower but that for grainiess was higher.Both visual evaluations for sharpness and graininess were lower with higher kV X rays, Visual graininess was closely correlated with the Wiener spectrum, but sharpness was only slightly correlated with the MTF. The sharpness of the asymmetric systems was inferior to that of the conven-tional ratio of 1 : 2 for the front and back screens should be applied for clinical use of the asymmetric systems.

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