  Dual-energy imaging is a clinically well-established technique that offers
several advantages over conventional X-ray imaging. By performing measurements
with two distinct X-ray spectra, differences in energy-dependent attenuation
are exploited to obtain material-specific information. This information is used
in various imaging applications to improve clinical diagnosis. In recent years,
grating-based X-ray dark-field imaging has received increasing attention in the
imaging community. The X-ray dark-field signal originates from ultra
small-angle scattering within an object and thus provides information about the
microstructure far below the spatial resolution of the imaging system. This
property has led to a number of promising future imaging applications that are
currently being investigated. However, different microstructures can hardly be
distinguished with current X-ray dark-field imaging techniques, since the
detected dark-field signal only represents the total amount of ultra
small-angle scattering. To overcome these limitations, we present a novel
concept called dual-energy X-ray dark-field material decomposition, which
transfers the basic material decomposition approach from attenuation-based
dual-energy imaging to the dark-field imaging modality. We develop a physical
model and algorithms for dual-energy dark-field material decomposition and
evaluate the proposed concept in experimental measurements. Our results suggest
that by sampling the energy-dependent dark-field signal with two different
X-ray spectra, a decomposition into two different microstructured materials is
possible. Similar to dual-energy imaging, the additional
microstructure-specific information could be useful for clinical diagnosis.
