Dark Field Sensitivity In Single Mask Edge Illumination Lung Imaging

Abstract

X-ray phase contrast imaging is a rapidly evolving field, covering a range of different imaging methods. Its integration in the daily medical imaging routines, however, has proven to be difficult, despite encouraging results. In addition to the phase information, small angle X-ray scattering information is accessible through the so called dark field signal. The dark field signal holds great potential for lung imaging applications due to its ability to detect sub-pixel structures. Edge illumination, an incoherent form of phase contrast imaging, is particularly promising due to its low coherence requirements. A remaining issue in conventional edge illumination phase contrast imaging, however, is the absorption of photons by the detector mask, as these photons contribute to the dose but not to the image. In this work, we explore the dark field potential of a setup without detector mask for lung imaging through Monte Carlo simulations. In order to approximate the irregular shape of alveoli, surface roughness is taken into account.

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

“…In the proposed approach, the grating bars are essentially modelled as purely absorbing 3D objects, where the absorption is calculated from attenuation coefficients through the Lambert-Beer law. Whereas this is obviously an approximation compared to a full MC grating bar model that includes explicit scattering events and refraction [40,41], it provides a higher level of simulation detail than the oftenused projection approximation (i.e. infinitely flat gratings).…”

“…(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].…”

“…X-rays can, for example, intersect the grating bars under an angle, impacting the effective distance traveled through the material. To incorporate these effects, grating bars are modelled as full 3D objects [21,22,40,41]. Three-dimensional MC models of membranes have been used for simulating speckle-based imaging as well [45].…”

“…Hence, geometrical optics can be used to describe image formation and phase shifts are modelled as refraction effects [38,39]. As interference modeling is no longer required, the simulation can be performed entirely in GATE, as demonstrated in earlier work [40,41].…”

Augmenting a conventional x-ray scanner with edge illumination-based phase contrast imaging: how to design the gratings

“…Although originally intended for combination with wave optics to perform XPCI simulations of grating-based interferometry, we have demonstrated in earlier work the full-MC simulation of EI experiments using our GATE-based tool. 9,11 In the MC framework, the standard approach is to model grating bars as 3D objects in the simulation, with energy-dependent attenuation properties following from the material. In this work, a virtual grating approach 12 is used to impose grating parameter variations post-simulation, which reduces the total simulation time.…”