Local versus whole breast volumetric breast density assessments and implications

Mammographic breast density is very important in the area of cancer risk evaluation, dosimetry and image quality optimization. Many studies have shown that a breast consisting of 50% glandular and 50% adipose tissues is not a representative model of typical breast composition, as the mean volumetric breast density has been found to be less than 20%, much lower than the commonly assumed value of 50/50. In this paper we investigate the characteristics of local breast density distribution of a breast in a large population. We find that the maximum local breast density, calculated from a densest region of a breast, is about 2.3X as high as the mean whole breast density. Therefore the maximum local breast density seems to match the 50/50 model better. Since modern mammography systems employ automatic exposure control (AEC) to ensure acceptable image quality for dense regions of a breast, and since the local breast density over AEC sensor regions often fall into the range of 40% and higher, the 50/50 breast model and physical phantoms should continue to be used in development of x-ray technique and clinical evaluation of mammography systems.