title: Interpretation of dark-field contrast and particle-size selectivity in grating interferometers.
abstract: In grating-based x-ray phase sensitive imaging, dark-field contrast refers to the extinction of the interference fringes due to small-angle scattering. For configurations where the sample is placed before the beamsplitter grating, the dark-field contrast has been quantified with theoretical wave propagation models. Yet when the grating is placed before the sample, the dark-field contrast has only been modeled in the geometric optics regime. Here we attempt to quantify the dark-field effect in the grating-before-sample geometry with first-principle wave calculations and understand the associated particle-size selectivity. We obtain an expression for the dark-field effect in terms of the sample material's complex refractive index, which can be verified experimentally without fitting parameters. A dark-field computed tomography experiment shows that the particle-size selectivity can be used to differentiate materials of identical x-ray absorption.
authors.affiliation: Laboratory of Imaging Physics, Translational Medicine Branch, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Susanna K
authors.initials: SK
authors.lastname: Lynch
authors.forename: Vinay
authors.initials: V
authors.lastname: Pai
authors.forename: Julie
authors.initials: J
authors.lastname: Auxier
authors.forename: Ashley F
authors.initials: AF
authors.lastname: Stein
authors.forename: Eric E
authors.initials: EE
authors.lastname: Bennett
authors.forename: Camille K
authors.initials: CK
authors.lastname: Kemble
authors.forename: Xianghui
authors.initials: X
authors.lastname: Xiao
authors.forename: Wah-Keat
authors.initials: WK
authors.lastname: Lee
authors.forename: Nicole Y
authors.initials: NY
authors.lastname: Morgan
authors.forename: Han Harold
authors.initials: HH
authors.lastname: Wen
mesh_terms: D005290:Ferric Compounds; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007368:Interferometry / Q000379:methods* / Q000706:statistics & numerical data; D053768:Metal Nanoparticles; D008858:Microscopy, Phase-Contrast; D008863:Microspheres; D008962:Models, Theoretical; D055620:Optical Phenomena; D010316:Particle Size; D011857:Radiographic Image Interpretation, Computer-Assisted; D012031:Refractometry; D014057:Tomography, X-Ray Computed; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide