The accuracy of geometric approximation of the mamilla in mammograms

Abstract The mammilla is an important landmark when judging mammograms. A method of finding the mammilla used by radiologists and within computer-aided mammography is based on the geometrical assumption that the mammilla is located at the point on the breast border that has the furthest distance perpendicular to the pectoralis muscle. This assumption has been widely accepted, and the aim of this paper is to present an evaluation of the accuracy of this method. Our evaluation, based on the Mammographic Image Analysis Society (MIAS) database, gave a correct estimate of the position of the mammilla for 125 images out of 305 (41%). In 62% of the cases, the geometrical approximation yielded a position within the mammilla, and in 74% of the cases, the error was less than the average extension of the mammilla. However, about 70% of the mammograms used for evaluation are inadequate in some sense and this affects the estimated position in a negative fashion. Theoretical studies conclude that the geometrical assumption is not very sensitive to disturbances in the estimate of the pectoralis direction, but to fluctuations in the extracted breast border.