X线照片斑点的自相关函数的测试探讨

Research on testing of ACF of radiographic mottling

目的：测试Ｘ线照片斑点的自相关函数（ａｕｔｏ－ｃｏｒｅｌａｔｉｏｎｆｕｎｃｔｉｏｎ，ＡＣＦ）。材料与方法：对Ｆｕｊｉ（ＣａＷＯ４），Ｆｕｊｉ（ＢａＦＣｌＥｕ），天津Ｘ线胶片（ＣａＷＯ４）和天津Ｘ线胶片（ＢａＦＣｌＥｕ）４种屏－片组合系统，在同一摄影条件下获得Ｘ线照片，用显微密度计对其进行扫描取得Ｘ线照片的密度分布曲线Ｄ（Ｘ），作为离散型随机信号来处理，计算出４种屏－片系统的Ｘ线照片斑点的ＡＣＦ值。结果：与ＢａＦＣｌＥｕ组合的Ｘ线照片斑点的ＡＣＦ值比与ＣａＷＯ４组合的屏片系统的大。结论：ＢａＦＣｌＥｕ增感屏因结构颗粒大，对Ｘ线照片影响大（或相关性强），控制Ｘ线照片斑点ＡＣＦ值的主要措施是，使增感屏的颗粒不宜过大。

Purpose: To test ACF(auto correlation function) of granules on radiograph. Materials and methods: With four kinds of screen film systems Fuji/CaWO 4, Tianjin/CaWO 4, Fuji/(BaFCl∶Eu) and Tianjin/(BaFCl∶Eu), radiographs were obtained under the same exposure conditions. Through sanning these radiographs with microdensitometer the density distribution curves D(x) were obtained. There curves could be recognized as discrete random signals. By processing the curves, the ACF values of the radiographic mottling of these films were calculated. Results: the ACF of BaFCl∶Eu was greater than that of CaWO 4. Conclusion: The larger the granules of film screens, the greater the value of ACF. The method of controlling ACF is to reduce the size of screen granules.