Applications of the median filter to digital radiographic images

It is well known that Digital Subtraction Angiography (DSA) images suffer from the influence of noise. Linear filters have been applied to DSA images with some success but are known to introduce image degradation. It is particularly important that edge details be preserved in DSA images since the outline of vessels frequently contains the diagnostically useful information. The non-linear median filter possesses the property of removing spurious noise while preserving edge detail in an image. In the work presented here the difficulties of applying a median filter in two dimensions to the cartesian matrix of a typical image are investigated. The development of a suitable noise-added test image for this purpose is presented.