Correspondences between microcalcification projections on two mammographic views acquired with digital systems.

In this paper, we have proposed an algorithm for automatic matching of MC projections viewed on two mammograms of the same breast. The implemented algorithm consists in three steps. From five morphological features of the MC, a similarity function was built between each MC of the first image of the pair, and each MC of the second image. These values quantified the resemblance between each pair of MC and permitted, for a given MC of the first image, to sort the MC of the second image which could be matched to it. From the geometry of the system providing the pairs of images being analysed, we derived some geometrical constraints that must be satisfied by corresponding MC. In order to take into account the fact that due to breast deformation, the corresponding MC is often off the classical epipolar line constructed on the basis of stereovision assumption, we instead consider an epipolar strip on both side of the approximated epipolar line. The MC of the second image which was out of that strip was eliminated. Then a coefficient was applied to the remaining MC that took into account their distances to the approximated epipolar line. Finally, the selection procedure was used to pick out the right pair. In order to test our algorithm, we compared the result it yielded with those coming from two operators who matched a number of MC with confidence. A concordance of 78.43% was obtained between confident manual matching and automatic matching. Since this algorithm was designed to be part of a tool for 3D reconstruction of microcalcification clusters, we reconstructed some clusters with manual matching and automatic matching and compared the shapes of the clusters obtained in these two ways. The resemblance in some cases was very good and average in a number of others. This suggests that our algorithm should be improved. Therefore, apart from ongoing effort to introduce other constraints, we believe that taking into account the third view provided by the imaging system could be of great help. We shall soon explore this possibility. Overall, we believe that despite the failure of our tool in some cases it can already at this stage be used with some confidence.