Hruska CB, et al. - For the assessment of background parenchymal uptake (BPU; identified as a breast cancer risk factor), a new quantitative method was tested focusing on its reproducibility, comparing quantitative results with previously established subjective BPU categories, and examining the link between quantitative BPU and breast cancer risk. Using a simple region-of-interest analysis tool, nonradiologist operators could reliably perform quantitative measurement of BPU, defined as the ratio of average counts in fibroglandular tissue relative to that in fat. Independent of mammographic density and hormonal factors, quantitative BPU was identified as a functional imaging biomarker of breast cancer risk, like results obtained with subjective BPU categories.