A BREAST DENSITY INDEX FOR DIGITAL MAMMOGRAMS BASED ON RADIOLOGISTS RANKING

The purpose of this study was to develop and evaluate a computerized m ethod of calculating a breast density index (BDI) from digitized mammo grams that was designed specifically to model radiologists' perception of breast density. A set of 153 pairs of digitized mammograms (cranio -caudal, CC, and mediolateral oblique, MLO, views) were acquired and p reprocessed to reduce detector biases. The sets of mammograms were ord ered on an ordinal scale (a scale based only on relative rank-ordering ) by two radiologists, and a cardinal (an absolute numerical score) BD I value was calculated from the ordinal ranks. The images were also as signed cardinal BDI values by the radiologists in a subsequent session . Six mathematical features (including fractal dimension and others) w ere calculated from the digital mammograms, and were used in conjuncti on with single value decomposition and multiple linear regression to c alculate a computerized BDI. The linear correlation coefficient betwee n different ordinal ranking sessions were as follows: intraradiologist intraprojection (CC/CC): r = 0.978; intraradiologist interprojection (CC/MLO): r = 0.960; and interradiologist intraprojection (CC/CC): r = 0.968. A separate breast density index was derived from three separat e ordinal rankings by one radiologist (two with CC views, one with the MLO view). The computer derived BDI had a correlation coefficient (r) of 0.907 with the radiologists' ordinal BDI. A comparison between rad iologists using a cardinal scoring system (which is closest to how rad iologists actually evaluate breast density) showed r = 0.914. A breast density index calculated by a computer but modeled after radiologist perception of breast density may be valuable in objectively measuring breast density. Such a metric may prove valuable in numerous areas, in cluding breast cancer risk assessment and in evaluating screening tech niques specifically designed to improve imaging of the dense breast. C opyright (C) 1998 by W.B. Saunders Company.