Thickness correction of mammographic images by anisotropic filtering and interpolation of dense tissue

Without image processing, the dynamic range of display systems is too small to optimally display both the interior and the peripheral zone of a compressed breast. To overcome manual adjustment of contrast, we propose an algorithm for peripheral enhancement of digital or digitized mammograms. This is done by virtually adding homogeneous tissue at the peripheral zone, where the breast comes loose from the compression paddle. The gradual signal increase due to a smaller breast thickness near the breast edge is estimated by the solution of the anisotropic diffusion equation. The conductivity is set small in the direction perpendicular to the breast edge, and large in the parallel direction. By this, large conductivities (much blurring) can be applied, while undesirable artifacts that would be caused by isotropic filtering are minimized. This measure is not always enough to prevent some reduction of relevant contrast. Therefore, dense tissue along parallel curves to the breast edge is interpolated before smoothing the image. Anisotropic diffusion filtering and dense tissue interpolation are both new techniques to improve peripheral enhancement. Comparison with some other methods showed that our approach performs at least as good as other methods.