Estimating Breast Thickness for Dual-Energy Subtraction in Contrast-Enhanced Digital Mammography: A Theoretical Model

Dual-energy contrast-enhanced digital mammography (DE CE-DM) images the perfusion and vasculature of the breast using an iodinated contrast agent. High-energy (HE) and low-energy (LE) images of the breast are acquired; the DE image is obtained by a weighted logarithmic subtraction of the image pair. We hypothesized that the optimal DE subtraction weighting factor, w, is dependent on three parameters: breast thickness, kV, and filter material. We simulated the attenuation of x-rays through breasts of thicknesses ranging from 0.5 to 10 cm using different filter and kV combinations. The glandularity of the phantom for a given thickness was varied using different combinations of adipose and glandular tissues. We calculated the logarithm of the LE and HE signal intensities. For a given kV-filter pair, the signals decrease with increasing tissue thickness and glandularity. The DE weighting factor is thickness-dependent, and it decreases with increasing energy difference between the LE-HE kV pairs. These results facilitate the subtraction of tissue in the periphery of the breast, and aid in discriminating between contrast agent uptake in glandular tissue and subtraction artefacts.