A physical model of multiple-image radiography

Abstract

We recently proposed a phase-sensitive x-ray imaging method called multiple-image radiography (MIR), which is an improvement on the diffraction-enhanced imaging technique. MIR simultaneously produces three images, depicting separately the effects of absorption, refraction and ultra-small-angle scattering of x-rays, and all three MIR images are virtually immune to degradation caused by scattering at higher angles. Although good results have been obtained using MIR, no quantitative model of the imaging process has yet been developed. In this paper, we present a theoretical prediction of the MIR image values in terms of fundamental physical properties of the object being imaged. We use radiative transport theory to model the beam propagation, and we model the object as a stratified medium containing discrete scattering particles. An important finding of our analysis is that the image values in all three MIR images are line integrals of various object parameters, which is an essential property for computed tomography to be achieved with conventional reconstruction methods. Our analysis also shows that MIR truly separates the effects of absorption, refraction and ultra-small-angle scattering for the case considered. We validate our analytical model using real and simulated imaging data.

Artifacts in X-ray Dark-Field Tomography

“…Originally developed for application to analyzer-based imaging [3], Kelashvili et al developed a radiative transport model that is independent of the utilized imaging method [4]. The local scattering strength in the sample  s (x, z) is connected to the total scattering width  det at the position of the detector.…”

“…Thus, standard filtered-back projection [4] is applicable to scattering, which opens the possibility for quantitative darkfield tomography.…”

“…Therewith, a so-called phase stepping curve (PSC) is obtained for each pixel, which can then be analyzed in order to yield the three different kinds of contrast. Based on a theoretical description of a small scattering contribution to the image formation process [3], Wang et al established a first approach to quantitative dark-field tomography with the grating interferometer [4]. However, this approach is based on several approximations, and the artifacts that arise from violations of these approximations are still unknown.…”

Emphysema diagnosis using X-ray dark-field imaging at a laser-driven compact synchrotron light source

“…Reflection from the analyzer crystal only occurs for X-rays in a small angular range meeting the Bragg condition of the crystal. Tilting the crystal while monitoring the intensity in each pixel generates a rocking curve, from which absorption, phase, and small-angle scattering information of the sample can be extracted (17,18). An application of this technique to mouse lung measurements has been demonstrated by Kitchen et al (19).…”

Multi-modal hard x-ray imaging with a laboratory source using selective reflection from a mirror

“…In addition, single or multiple refraction shifts produced by features whose size is below the resolution limit are not directly resolved but rather contribute to an apparent decoherence (i.e. reduction of contrast) in the phase contrast image [20][21][22][23][24][25][26]. Such "unresolved" refraction effects are accounted for via ultra-small angle scattering.…”