title: A generalized quantitative interpretation of dark-field contrast for highly concentrated microsphere suspensions.
abstract: In X-ray grating interferometry, dark-field contrast arises due to partial extinction of the detected interference fringes. This is also called visibility reduction and is attributed to small-angle scattering from unresolved structures in the imaged object. In recent years, analytical quantitative frameworks of dark-field contrast have been developed for highly diluted monodisperse microsphere suspensions with maximum 6% volume fraction. These frameworks assume that scattering particles are separated by large enough distances, which make any interparticle scattering interference negligible. In this paper, we start from the small-angle scattering intensity equation and, by linking Fourier and real-space, we introduce the structure factor and thus extend the analytical and experimental quantitative interpretation of dark-field contrast, for a range of suspensions with volume fractions reaching 40%. The structure factor accounts for interparticle scattering interference. Without introducing any additional fitting parameters, we successfully predict the experimental values measured at the TOMCAT beamline, Swiss Light Source. Finally, we apply this theoretical framework to an experiment probing a range of system correlation lengths by acquiring dark-field images at different energies. This proposed method has the potential to be applied in single-shot-mode using a polychromatic X-ray tube setup and a single-photon-counting energy-resolving detector.
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: Spyridon
authors.initials: S
authors.lastname: Gkoumas
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.
authors.forename: Pablo
authors.initials: P
authors.lastname: Villanueva-Perez
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.|Institute for Biomedical Engineering University and ETH Zürich, 8092 Zürich, Switzerland.
authors.forename: Zhentian
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.|Institute for Biomedical Engineering University and ETH Zürich, 8092 Zürich, Switzerland.|Department of Physics and IMM-CNR, University of Catania, 64 via S. Sofia, I-95123 Catania, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Romano
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.|Institute for Biomedical Engineering University and ETH Zürich, 8092 Zürich, Switzerland.
authors.forename: Matteo
authors.initials: M
authors.lastname: Abis
authors.affiliation: Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland.|Institute for Biomedical Engineering University and ETH Zürich, 8092 Zürich, Switzerland.
authors.forename: Marco
authors.initials: M
authors.lastname: Stampanoni