X-ray Phase-contrast Simulations of Fibrous Phantoms using GATE

Abstract

The overall importance of x-ray phase-contrast imaging techniques has grown substantially due to their ability to generate contrast in a range of situations where traditional absorption imaging falls short. Monte Carlo simulations are a valuable tool for benchmarking and testing new acquisition and reconstruction techniques, as well as optimisation of the system and components design. GATE, an open source application layer on top of the Geant4 simulation software, is a versatile Monte Carlo tool for various types of medical imaging simulations. Currently, however, tools intended for phase-contrast imaging are not yet available within GATE. In this work, we introduce grating-based x-ray phase-contrast simulations in GATE, with specific focus on phantoms with fibrous microstructures. The simulations are based on a combination of Monte Carlo simulations in GATE for modelling the x-ray interactions in the sample, and subsequent numerical wave propagation in the interferometer, modelled in MATLAB. We show simulated computed tomography results for grating interferometry.

Virtual grating approach for Monte Carlo simulations of edge illumination-based x-ray phase contrast imaging

“…In general, modelling the effect of the gratings is a crucial aspect of the simulation. Different approaches exist, which can be roughly divided in three categories: (1) modelling the grating as a plane (2D) [18,26,27,44,23,14,15,25,24,32,20],…”

“…(2) modelling the grating as a volume with bars extending along the direction of the optical axis (3D) [21,22,40,41], or (3) simulation frameworks where the effect of the grating is accounted for implicitly, without introducing the gratings as components in the simulation [16,33,31]. Two-dimensional (flat) grating models are common in, but not restricted to, wave-optics simulations and involve either an idealised binary representation of the grating [18,26,27,44] or application of a complex transmission function (projection approximation) [23,14,15,25,24,32,20]. However, assuming the gratings are infinitesimally thin is not always a valid approximation.…”

“…XPCI simulators are often either based on wave optics calculations [13,14,15,16], Monte Carlo (MC) code [17,18,19,20,21,22], or a combination thereof [23,24,25,26,27,28]. In addition, ray tracing-based [29,30,31,32] and empirical methods [33] have been reported.…”

“…Some of these studies have explicitly included simulations for EI [15,18,19,30,21,22]. In earlier work [26,27], we have demonstrated the hybrid (MC and wave optics) simulation of XPCI for GBI using an extended version of GATE, a Geant4-based MC framework [34,35,36]. Within this framework, the MC code is used to generate a wavefront, which is subsequently propagated through the gratings towards the detector using wave optics.…”

Towards Monte Carlo simulation of X-ray phase contrast using GATE

“…Scattered photons are for example handled separately in order to add them as incoherent effects to the intensity of the wave front calculated by the Fresnel propagation [29]. To accomodate wave and particle properties, the simulation framework is usually split in several stages as in [30][31][32], where the MC stage is used to generate a phase space which is then converted into a complex wave amplitude for propagation in the optics. Diffraction has also been tackled using the Huygens-Fresnel principle [33] using a post-processing step at the detector stage.…”