Speaker
Description
Speckle-based X-ray dark-field imaging is attractive because it can deliver small-angle scattering contrast with a comparatively simple optical setup, but quantitative modeling of weakly absorbing microstructures in hydrated environments still requires improved treatment of multiple refraction and unresolved ultra-small-angle X-ray scattering (USAXS). Building on the wave-optics simulation framework of Meyer et al. [1] and motivated by USAXS formulations used in speckle/beam-tracking studies, we developed a plane-wave monochromatic multi-slice simulation pipeline that extends the projection-approximation model with slice-by-slice propagation through the sample, explicit particle-in-water embedding, and detector-plane USAXS blur described by a hybrid model combining an isotropic bulk term with a weak phase-gradient-dependent anisotropic term. Simulations were performed at 17.5 keV with a five-layer random diffuser, a 50 um pixel detector, and a 130 um-thick water cell containing a sparse monolayer of eight 120 um polystyrene-like spheres.
The water-blank normalization effectively removed most box- and water-related attenuation while preserving particle-specific dark-field contrast. Residual normalized transmission deviations were only on the order of 10-4 and the absorption CNR was 1.72, whereas the dark-field extinction remained strong and spatially localized to the particle footprints, with -ln(D) = 0.2349 in particle regions versus 0.0052 in the surrounding local background. The resulting dark-field CNR reached 29.18, corresponding to an approximately 17-fold contrast advantage over absorption. The retrieved mean speckle size was 161.7 um (about 3.23 detector pixels), and the equivalent detector-plane USAXS blur was 0.67 detector pixels. These results show that explicit multi-slice propagation and USAXS-aware modeling can recover robust dark-field signatures from weakly absorbing particles embedded in water, where conventional attenuation contrast is strongly suppressed.