  Spectral imaging is the acquisition of multiple images of an object at
different energy spectra. In mammography, dual-energy imaging (spectral imaging
with two energy levels) has been investigated for several applications, in
particular material decomposition, which allows for quantitative analysis of
breast composition and quantitative contrast-enhanced imaging. Material
decomposition with dual-energy imaging is based on the assumption that there
are two dominant photon interaction effects that determine linear attenuation:
the photoelectric effect and Compton scattering. This assumption limits the
number of basis materials, i.e. the number of materials that are possible to
differentiate between, to two. However, Rayleigh scattering may account for
more than 10% of the linear attenuation in the mammography energy range. In
this work, we show that a modified version of a scanning multi-slit spectral
photon-counting mammography system is able to acquire three images at different
spectra and can be used for triple-energy imaging. We further show that
triple-energy imaging in combination with the efficient scatter rejection of
the system enables measurement of Rayleigh scattering, which adds an additional
energy dependency to the linear attenuation and enables material decomposition
with three basis materials. Three available basis materials have the potential
to improve virtually all applications of spectral imaging.
