Outlining and categorising mammographic breast density: expert radiologist perception

The main aim of this study is to investigate the outlining and categorising of mammographic breast density by expert radiologists in order to help to understand what kind of region radiologists perceive as breast density and how they assess the density of a mammogram. It investigates inter-radiologist variability in breast density outlining and assessment. Forty-five normal cranio-caudal view mammograms with a range of appearances of breast density were presented to twenty radiologists. Each participant was asked to manually outline any mammographic breast density using an interactive pen tablet and to visually classify mammographic breast density in two ways by using the BI-RADS density categorization system by the American College of Radiology, and by estimating the percentage of area of mammographic breast density. Large differences were found in breast density outlining for all BI-RADS density categories. Scattered and patchy breast density appeared to be associated with large variation in outlining. There was moderate inter-radiologist agreement in BI-RADS density categorising (Kappa = 0.489). Breast density is a complex radiological feature that impacts upon assessment consistency.