Elimination of gridlines by using non linear filter in mammograhic image

The mammographic X-ray equipment uses a radiographic grid in order to remove the scatter radiation and improve image contrast. The grid causes striped lines to appear on the film and may degrade diagnostic information. In this study, we propose a new method which reduces the noise caused by the grid on mammographic film using non linear image filtering. We performed median filtering and the V-filtering as a method of image filtering. We consider the region of the filters to eliminate gridlines effectively. In the experiment using the breast phantom, we calculated signal to noise (SN) ratios in the micro calcifications region. The SN ratio of the image processed by median filtering after the V-filtering was increased. Furthermore, we evaluated the noise by using the power spectrum in a line profile by fast Fourier transform. The value of the power spectrum at a frequency that represented the periodic noise made by the gridlines was decreased. We could confirm the validity of image filtering. It was found out that our proposed image filtering method was useful for eliminating gridlines in the X-ray image.