Figure 2.

Illustration of the calibration procedure and spectral breast‐density measurement for a: Unprocessed high‐ and sum‐energy images (raw counts); nonspectral calibration on a PMMA step wedge; high‐ and sum‐energy mammograms; spectral calibration on tissue‐equivalent material and PMMA‐to‐thickness and ‐density LUTs; thickness and density maps; calculation of density and volume measures. Iso‐thickness and ‐density lines (dotted) and calibration points (circles) are indicated in the LUTs. Note that the thickness and density maps are normally not displayed to the user but are an internal part of the algorithm.