Realistic wave-optics simulation of X-ray phase-contrast imaging at a human scale (original) (raw)
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New developments in simulating X-ray phase contrast imaging
2007
A deterministic algorithm simulating phase contrast (PC) x-ray images for complex 3dimensional (3D) objects is presented. 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 presented algorithm are examined with the help of some relevant examples.
X-ray phase contrast image simulation
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
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.
Applied optics, 2013
We derive a Fourier formulation of coded-aperture x-ray phase-contrast imaging, based on the wave theory of optics in the Fresnel approximation. We use this model to develop a flexible, efficient, and general simulation algorithm that can be easily adapted to other implementations of x-ray phase contrast imaging. Likewise, the algorithm enables a simple extension to 2D aperture designs, different acquisition schemes, etc. Problems related to numerical implementation of the algorithm are analyzed in detail, and simple rules are derived that enable us to avoid or at least mitigate them. Finally, comparisons with experimental data and data obtained with a different simulation algorithm are presented to validate the model and demonstrate its advantages in practical implementations. This also enabled us to demonstrate an increase in computational speed of more than one order of magnitude over a previous algorithm.
Journal of Synchrotron Radiation, 2014
Phase-sensitive X-ray imaging shows a high sensitivity towards electron density variations, making it well suited for imaging of soft tissue matter. However, there are still open questions about the details of the image formation process. Here, a framework for numerical simulations of phase-sensitive X-ray imaging is presented, which takes both particle-and wave-like properties of X-rays into consideration. A split approach is presented where we combine a Monte Carlo method (MC) based sample part with a wave optics simulation based propagation part, leading to a framework that takes both particle-and wavelike properties into account. The framework can be adapted to different phasesensitive imaging methods and has been validated through comparisons with experiments for grating interferometry and propagation-based imaging. The validation of the framework shows that the combination of wave optics and MC has been successfully implemented and yields good agreement between measurements and simulations. This demonstrates that the physical processes relevant for developing a deeper understanding of scattering in the context of phase-sensitive imaging are modelled in a sufficiently accurate manner. The framework can be used for the simulation of phase-sensitive X-ray imaging, for instance for the simulation of grating interferometry or propagation-based imaging.
X-ray phase-contrast imaging: from pre-clinical applications towards clinics
Physics in Medicine and Biology, 2012
Phase-contrast x-ray imaging (PCI) is an innovative method that is sensitive to the refraction of the x-rays in matter. PCI is particularly adapted to visualize weakly absorbing details like those often encountered in biology and medicine. In past years, PCI has become one of the most used imaging methods in laboratory and preclinical studies: its unique characteristics allow high contrast 3D visualization of thick and complex samples even at high spatial resolution. Applications have covered a wide range of pathologies and organs, and are more and more often performed in vivo. Several techniques are now available to exploit and visualize the phase-contrast: propagation-and analyzer-based, crystal and grating interferometry and non-interferometric methods like the coded aperture. In this review, covering the last five years, we will give an overview of the main theoretical and experimental developments and of the important steps performed towards the clinical implementation of PCI.
Optics Express, 2010
X-ray phase contrast imaging is a very promising technique which may lead to significant advancements in medical imaging. One of the impediments to the clinical implementation of the technique is the general requirement to have an x-ray source of high coherence. The radiation physics group at UCL is currently developing an x-ray phase contrast imaging technique which works with laboratory x-ray sources. Validation of the system requires extensive modelling of relatively large samples of tissue. To aid this, we have undertaken a study of when geometrical optics may be employed to model the system in order to avoid the need to perform a computationally expensive wave optics calculation. In this paper, we derive the relationship between the geometrical and wave optics model for our system imaging an infinite cylinder. From this model we are able to draw conclusions regarding the general applicability of the geometrical optics approximation.
International Journal of Modern Physics: Conference Series, 2014
X-ray phase contrast imaging (XPCi) provides a much higher visibility of low-absorbing details than conventional, attenuation-based radiography. This is due to the fact that image contrast is determined by the unit decrement of the real part of the complex refractive index of an object rather than by its imaginary part (the absorption coefficient), which can be up to 1000 times larger for energies in the X-ray regime. This finds applications in many areas, including medicine, biology, material testing, and homeland security. Until lately, XPCi has been restricted to synchrotron facilities due to its demanding coherence requirements on the radiation source. However, edge illumination XPCi, first developed by one of the authors at the ELETTRA Synchrotron in Italy, substantially relaxes these requirements and therefore provides options to overcome this problem. Our group has built a prototype scanner that adapts the edge-illumination concept to standard laboratory conditions and extend...
Quantitative edge illumination x-ray phase contrast tomography
Developments in X-Ray Tomography IX, 2014
This article discusses two experimental setups of edge illumination (EI) x-ray phase contrast imaging (XPCi) as well as the theory that is required to reconstruct quantitative tomographic maps using established methods, e.g. filtered back projection (FBP). Tomographic EI XPCi provides the option to reconstruct volumetric maps of different physical quantities, amongst which are the refractive index decrement from unity and the absorption coefficient, which can be used for dual-mode imaging. EI XPCi scans of a custom-built wire phantom using synchrotron and x-ray tube generated radiation were carried out, and tomographic maps of both parameters were reconstructed. This article further discusses the theoretical basis for the tomographic reconstruction of images showing combined phase and attenuation contrast. Corresponding experimental results are presented.