The split and merge technique [30] is the other classical region-based segmentation method. As the name indicates, the process consists of recursively splitting the image until all regions confirm to a homogeneity criterion. In an accompanying step, all adjacent regions satisfying a second homogeneity criterion are merged. However, to our knowledge, for mammographic mass segmentation, this approach has only been used by Rangayyan et al. [151] who, beginning with a hand-selected region of interest containing a single mass, used this technique to approximate its boundary by polygons.