  Measurements of breast density have the potential to improve the efficiency
and reduce the cost of screening mammography through personalized screening.
Breast density has traditionally been evaluated from the dense area in a
mammogram, but volumetric assessment methods, which measure the volumetric
fraction of fibro-glandular tissue in the breast, are potentially more
consistent and physically sound. The purpose of the present study is to
evaluate a method for measuring the volumetric breast density using
photon-counting spectral tomosynthesis. The performance of the method was
evaluated using phantom measurements and clinical data from a small population
(n=18). The precision was determined to 2.4 percentage points (pp) of
volumetric breast density. Strong correlations were observed between
contralateral (R^2=0.95) and ipsilateral (R^2=0.96) breast-density
measurements. The measured breast density was anti-correlated to breast
thickness, as expected, and exhibited a skewed distribution in the range [3.7%,
55%] and with a median of 18%. We conclude that the method yields promising
results that are consistent with expectations. The relatively high precision of
the method may enable novel applications such as treatment monitoring.
