Novel use of single X-ray absorptiometry for measuring breast density.

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.