Automatic pectoral muscle segmentation on mammograms by straight line estimation and cliff detection

Mammograms, which are X-ray images of the female breast, are used widely by radiologists to screen for breast cancer. The first stage of any computerized analysis of the digitised mammogram is to divide the image into anatomically distinct regions. The pectoral muscle is one of these regions and it appears on mediolateral oblique views of mammograms. In this paper, the rationale and algorithms for fully automatic, two-part segmentation of the pectoral muscle are presented. The algorithm consists of (a) estimation of the muscle edge by a straight line; and (b) refinement of the detected edge by surface smoothing and edge detection in a restricted neighbourhood derived from the first estimate.