Masking procedures and measures of angular similarity for detection of bilateral asymmetry in mammograms

We propose a method to analyze bilateral asymmetry in mammograms based upon systematic comparison of paired mammographic strips of the right and left breasts of a patient. Similarity between corresponding directional structures was quantified by applying measures of similarity to the masked strips. A novel application of Moran´s index was designed to measure the angular covariance between rose diagrams related to the phase and magnitude responses of multidirectional Gabor filters. A set of 128 mammograms from the DDSM database, including 32 normal and 32 asymmetric pairs, was used to validate the procedure. The leave-one-patient-out method was used for cross-validation of the results. The best result, with an area under the receiver operating characteristic curve of 0.8435, was achieved using similarity measures on craniocaudal views and Fisher-linear discriminant analysis. The results indicate that the proposed techniques can be applied for computer-aided detection of bilateral asymmetry.