Breast density is one of the strongest known breast cancer risk factors. Breast density has primarily been measured by either categorical scores of the proportion of opacity on a screening mammogram or as a ratio of the delineated dense area to the total breast area on a mammogram. These methods are limited by their subjectivity, their lack of absolute reference standards, and lack of automation for clinical use.

We present a novel automated method for measuring breast composition we call Breast Compositional Density measured using single X-ray absorptiometry techniques, or BD_SXA. BD_SXA measures breast compositional density by comparing the opacity on the mammogram to two reference standards imaged with each breast. We present the mathematical derivation of BD_SXA, methods for correcting for radiographic nonuniformity in the mammogram, and in vitro measures of accuracy and repeatability. Using phantoms, BD_SXA has been shown to have a long-term repeatability of better than 2% for a breast composition range of 0 to 100% fibroglandular density.