Establishing correspondence in mammograms and tomosynthesis projections

We are developing a computer based aid for automated analysis of digital mammograms and digital breast tomosynthesis (DBT) images. The ultimate goal is to establish correspondence between regions in images obtained using different modalities. This paper is focused on establishing point correspondences between mammograms and DBT projections. Correspondence has been established utilizing two similarity criteria, one based on topology of prominent elongated anatomical structures, and another based on texture near the potential correspondence points. We evaluated robustness of the described technique with respect to variations in x-ray tube angle. The evaluation included 72 image pairs: 9 DBT projections from both left and right breasts of 4 women and corresponding mammograms. The evaluation was performed by a consensus between two trained observers. Two images with highlighted pairs of automatically established point correspondences were presented. The observers were asked to manually identify the correct correspondences and measure the displacement error. Points for which correspondences could not be manually identified were excluded. The topology method automatically generated an average of 12.2 correspondences per image pair, for which the average measured displacement error was 1.33 mm (N = 10.5). The texture method generated 18.6 correspondences with an average measured error of 1.80 mm (N = 14.7). The algorithms were found to be robust; the number of correspondences and the average displacement did not significantly change with variations in tube angle.