X-ray phase contrast image simulation

A deterministic algorithm is proposed to simulate phase contrast (PC) X-ray images for complex three-dimensional (3D) objects. This algorithm has been implemented in a simulation code named VXI (virtual X-ray imaging). The physical model chosen to account for PC technique is based on the Fresnel–Kirchhoff diffraction theory.The algorithm consists mainly of two parts. The first one exploits the VXI ray-tracing approach to compute the object transmission function. The second part simulates the PC image due to the wave front distortion introduced by the sample.In the first part, the use of computer-aided drawing (CAD) models enables simulations to be carried out with complex 3D objects. Differently from the VXI original version, which makes use of an object description via triangular facets, the new code requires a more “sophisticated” object representation based on non-uniform rational B-splines (NURBS).As a first step we produce a spatial high resolution image by using a point and monochromatic source and an ideal detector. To simulate the polychromatic case, the intensity image is integrated over the considered X-ray energy spectrum. Then, in order to account for the system spatial resolution properties, the high spatial resolution image (mono or polychromatic) is convolved with the total point spread function of the imaging system under consideration.The results supplied by the proposed algorithm are examined with the help of some relevant examples.