Quantifying image quality at breast periphery vs mammary gland in mammography using wavelet analysis

Use of high contrast film-screen systems in mammography, in combination wit h the fact that exposure parameters are selected to ensure good visualizati on of the mammary gland, results in overexposure of the film area correspon ding to the breast periphery, therefore decreasing image quality. The aim o f this work was to provide a quantitative evaluation of image quality at th e breast periphery compared with the mammary gland. To deal with the diffic ulties in quantification of image quality introduced by low contrast encoun tered at the breast periphery, wavelet analysis has been used for derivatio n of a contrast indicator (CI) and a noise indicator (NI), taking into acco unt local grey level variations. Gradient magnitude coefficients correspond ing to region of interest (ROI) grey level values are the basis of Cl defin ition. Mammary gland and breast periphery were sampled by equally spaced RO Is, the quantity of which was determined by a heuristic method. For NI defi nition, the power values of gradient magnitude coefficients corresponding t o the ROI were utilized. Image quality at the breast periphery compared wit h the mammary gland was evaluated using 150 craniocaudal images from the Di gital Database for Screening Mammography. Measurements were carried out usi ng a tool developed in our department. A 50% contrast decrease at the breas t periphery was observed, while noise decreased by approximately 2%.