Methods for improving the accuracy of a technique for estimating volumetric breast density are described. A breast tissue-equivalent phantom encompassing a range of thicknesses and compositions of tissue is used to evaluate the sources of error in the technique. The image acquisition parameters that can affect the accuracy of calibration are considered, and sensitivity to these factors is evaluated. The robustness of the technique was tested by obtaining calibration images on 24 mammography machines, at 18 different sites, over a period of 3 years. The ability to use a single calibration on all machines of a given model type was assessed by comparing effective linear attenuation coefficients of fat and fibroglandular tissues, derived from the calibration phantom images obtained from various machines.
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