X-ray propagation-based phase contrast imaging (XPCI) relies on the coherence of the X-ray beam to achieve contrast from phase shift by letting the beam propagate in free space, hence yielding a Fresnel or Fraunhofer diffraction pattern. This contrast regime arises in high resolution imaging, where it is used for tomography in a wide range of applications. The exploitation of such images requires a phase retrieval step, which has proven sensitive to noise in low spatial frequencies. It is thought that incoherent scattering in the sample might contribute to this noise. Therefore, several approaches to combine phase contrast and incoherent scattering have recently been proposed. To this aim, we propose a new way to simulate phase contrast based on the Wigner Distribution Function (WDF). In this framework, the exit wave of the sample is calculated through ray-tracing, which would allow accounting for effects including refraction and reflection. The interference is then calculated in the exit plane using the WDF, instead of in the detector plane, as is the case using classical methods. Images can then be simulated photon by photon, by first simulating incoherent scattering in the sample using a Monte Carlo particle transport code, followed by diffraction by probability sampling of the WDF. As a first demonstration of the framework, we simulate the double-slit experiment, as well as a variant with a scatterer in one of the slits. Since the double-slit has an analytical solution for the WDF, both in its standard form and with different amplitudes in each slit, this enables us to bypass the most challenging numerical difficulties for this initial demonstration.
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