Effect of tissue thickness variation in volumetric breast density estimation

A method is presnented for the estimation of dense breast tissue volume from full-field digital mammograms. The digital signal from the image is determined by using a physical signal propagation model that considers the incident x-ray spectrum and detector efficiency, assuming that the breast is composed of only adipose and firbroglandular tissue. The effect of an error in the breast thickness on the volumetric breast density (VBD) was studied using the model by replacing a curved thickness profile, as measured by optical photogrammetry on a compressed breast, by a constant thickness. It was found that a constant thickness approximation within 2% of the mean of the curved thickness is sufficient to keep the error within 5% VBD units for breasts of 10%, 25%, 50% density. Relying on the thickness readout of mammography units typically induces large errors in the VBD estimation.