Recently, in addition to the method for evaluating physically the quality of radiographic images, the method of psycological estimate has been proposed. It has been standard practice in which the final evaluation of radiographic images have been carried out by human vision. For this reason, we are not able to understand the process and references used in a physical evaluation. So we evaluated the Thurstone's Method of Paired Comparisons as a method of evaluating the plain skull radiographs, and have produced a scale. We evaluated sharpness, granularity, contrast, etc. and so the total image quality of plain skull radiographs. It indicated a strong relationship between total evaluation and sharpness of the plain skull radiographs. Since the preference value of the observer was able to be analyzed quantitatively by using the Thurstone method, it was possible to do a subjective evaluation of image quality on an interval scale. Thus, the analysis based on the interval scale was verified to be useful for a total evaluation.
