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Concordance of computer-extracted image features with BI-RADS descriptors for mammographic mass margin

The purpose of this study was to develop and evaluate computer-extracted features for characterizing mammographic mass margins according to BI-RADS spiculated and circumscribed categories. The mass was automatically segmented using an active contour model. A spiculation measure for a pixel on the mass boundary was defined by using the angular difference between the image gradient vector and the normal to the mass, averaged over pixels in a spiculation search region. For the circumscribed margin feature, the angular difference between the principal eigenvector of the Hessian matrix and the normal to the mass was estimated in a band of pixels centered at each point on the boundary, and the feature was extracted from the resulting profile along the boundary. Three MQSA radiologists provided BI-RADS margin ratings for a data set of 198 regions of interest containing breast masses. The features were evaluated with respect to the individual radiologists' characterization using receiver operating characteristic (ROC) analysis, as well as with respect to that from the majority rule, in which a mass was labeled as spiculated (circumscribed) if it was characterized as such by 2 or 3 radiologists, and non-spiculated (non-circumscribed) otherwise. We also investigated the performance of the features for consensus masses, defined as those labeled as spiculated (circumscribed) or nonspiculated (non-circumscribed) by all three radiologists. When masses were labeled according to radiologists R1, R2, and R3 individually, the spiculation feature had an area Az under the ROC curve of 0.90±0.04, 0.90±0.03, 0.88±0.03, respectively, while the circumscribed margin feature had an Az value of 0.77±0.04, 0.74±0.04, and 0.80±0.03, respectively. When masses were labeled according to the majority rule, the Az values for the spiculation and the circumscribed margin features were 0.92±0.03 and 0.80±±0.03, respectively. When only the consensus masses were considered, the Az values for the spiculation and the circumscribed margin features were 0.96±0.04 and 0.87±0.04, respectively. We conclude that the newly developed features had high accuracy for characterizing mass margins according to BI-RADS descriptors.