Edge Illumination X-ray Phase-contrast Imaging Research Articles

Angular sensitivity and spatial resolution in edge illumination X-ray phase-contrast imaging

Edge illumination (EI) is an X-ray phase-contrast imaging (XPCi) technique which bears high potential for applications in several fields, thanks to its simple experimental setup and to its applicability with conventional X-ray sources. In this context, the estimation of the phase sensitivity and spatial resolution achievable with EI is of particular importance, as it will enable assessing and quantifying the full potential of the technique. We present in this article a simple theoretical model that allows the analysis of these two quantities and of their dependence upon the different acquisition parameters. We believe that the obtained results will prove very useful for the design and optimization of future setups. Besides, we demonstrate experimentally that the simplicity of the EI setup does not come at the expense of the sensitivity; on the contrary, EI allows achieving very high angular resolutions.

On the origin of contrast in edge illumination X-ray phase-contrast imaging.

Edge illumination (EI) has emerged as an X-ray phase-contrast imaging (XPCi) modality which could present significant advantages in terms of translation to clinical and laboratory applications. In this paper, we model its signal through the use of the "transport of intensity" equation. The validity conditions for this approach and its relationship with previous theoretical models for EI XPCi are discussed. The proposed model enables a simple estimation of the different contributions to the signal, which is shown to complement previously obtained results. In particular, it allows taking into account the effect of both slowly and rapidly varying refraction angles, corresponding to large and small object features. The derived framework is then used to investigate the effect on the signal of the smoothness of the mask edges, of the blurring from the source size and of the width of the object edge.

Edge-illumination X-ray phase contrast imaging: matching the imaging method to the detector technology

X-Ray Phase Contrast Imaging (XPCI) has been arguably the hottest topic in X-ray imaging research over the last two decades, due to the significant advantages it can bring to medicine, biology, material science and many other areas of application. Considerable progress has recently been achieved, in terms of the first in vivo implementations at synchrotrons (notably at Elettra in Trieste), and of new XPCI methods working with conventional sources. Among the latter, edge-illumination (EI) is possibly one of the most promising in terms of mainstream translation, due to set-up simplicity, scalability and flux efficiency compared to other approaches. EI is indeed the only method working with a completely incoherent source: however, it was recently demonstrated that neither the ability to perform quantitative phase retrieval, nor the method's phase sensitivity are affected by the source's incoherence. Here its implementation with different detector technologies is discussed.

The effect of the spatial sampling rate on quantitative phase information extracted from planar and tomographic edge illumination x-ray phase contrast images

The effect of the spatial sampling rate on the quantitative phase information that can be retrieved from planar and tomographic edge illumination (EI) x-ray phase contrast imaging (XPCi) with a laboratory-based prototype scanner is analysed. The study is conducted on simulated and experimental data from a custom-built phantom. Optimal sampling rates, i.e. the minimum ones allowing the unambiguous extraction of quantitative phase measurements from the acquired data, are identified for planar and tomographic imaging. One of the key outcomes of this study is the demonstration that the optimal sampling rate in tomographic EI XPCi is low, allowing the implementation of low-dose volumetric imaging without having to compromise on quantitative accuracy.

Low-dose phase contrast tomography with conventional x-ray sources.

The edge illumination (EI) x-ray phase contrast imaging (XPCi) method has been recently further developed to perform tomographic and, thus, volumetric imaging. In this paper, the first tomographic EI XPCi images acquired with a conventional x-ray source at dose levels below that used for preclinical small animal imaging are presented. Two test objects, a biological sample and a custom-built phantom, were imaged with a laboratory-based EI XPCi setup in tomography mode. Tomographic maps that show the phase shift and attenuating properties of the object were reconstructed, and analyzed in terms of signal-to-noise ratio and quantitative accuracy. Dose measurements using thermoluminescence devices were performed. The obtained images demonstrate that phase based imaging methods can provide superior results compared to attenuation based modalities for weakly attenuating samples also in 3D. Moreover, and, most importantly, they demonstrate the feasibility of low-dose imaging. In addition, the experimental results can be considered quantitative within the constraints imposed by polychromaticity. The results, together with the method's dose efficiency and compatibility with conventional x-ray sources, indicate that tomographic EI XPCi can become an important tool for the routine imaging of biomedical samples.

Spatial resolution of edge illumination X-ray phase-contrast imaging.

We analyze the spatial resolution of edge illumination X-ray phase-contrast imaging and its dependence upon various experimental parameters such as source size, source-to-sample and sample-to-detector distances, X-ray energy and size of the beam-shaping aperture. Different propagation regimes, as well as the beam divergence and polychromaticity encountered with laboratory sources, are also considered. We show that spatial resolution in edge illumination phase-contrast imaging presents peculiar features compared to other X-ray phase-contrast techniques. In particular, in the direction orthogonal to the s or mask lines used to shape the beam, this can be better than both the pixel dimension and the projected source size. Numerical simulations based on Fresnel diffraction integrals are presented, which confirm the analytical predictions. The obtained results allow a simple estimation of the spatial resolution for edge-illumination phase imaging in both synchrotron and laboratory setups.

Edge illumination X-ray phase-contrast imaging: nanoradian sensitivity at synchrotrons and translation to conventional sources

Edge illumination is an X-ray phase-contrast imaging technique that can be efficiently applied to both synchrotron radiation and laboratory sources. Its implementation with these two types of setups is here described, and a recently developed method to perform quantitative retrieval of the object attenuation and refraction properties is presented. We report results obtained at two synchrotron radiation facilities and with one of the setups installed in our laboratories at University College London, which show that very high angular sensitivities can be obtained with this technique. The effect of different experimental parameters on the achievable sensitivity is also analyzed. The obtained results will be a useful guide for the design and optimization of future experimental layouts.

Theory and preliminary experimental verification of quantitative edge illumination x-ray phase contrast tomography

X-ray phase contrast imaging (XPCi) methods are sensitive to phase in addition to attenuation effects and, therefore, can achieve improved image contrast for weakly attenuating materials, such as often encountered in biomedical applications. Several XPCi methods exist, most of which have already been implemented in computed tomographic (CT) modality, thus allowing volumetric imaging. The Edge Illumination (EI) XPCi method had, until now, not been implemented as a CT modality. This article provides indications that quantitative 3D maps of an object's phase and attenuation can be reconstructed from EI XPCi measurements. Moreover, a theory for the reconstruction of combined phase and attenuation maps is presented. Both reconstruction strategies find applications in tissue characterisation and the identification of faint, weakly attenuating details. Experimental results for wires of known materials and for a biological object validate the theory and confirm the superiority of the phase over conventional, attenuation-based image contrast.

Proof-of-concept demonstration of edge-illumination x-ray phase contrast imaging combined with tomosynthesis

In this note we present the first proof-of-concept results on the potential effectiveness of the edge-illumination x-ray phase contrast method (in its ‘coded-aperture’ based lab implementation) combined with tomosynthesis. We believe that, albeit admittedly preliminary (e.g. we only present phantom work), these results deserve early publication in a note primarily for four reasons. First, we fully modelled the imaging acquisition method, and validated the simulation directly with experimental results. This shows that the implementation of the method in the new geometry is understood, and thus that it will be possible to use the model to simulate more complex scenarios in the future. Secondly, we show that a strong phase contrast signal is preserved in the reconstructed tomosynthesis slices: this was a concern, as the high spatial frequency nature of the signal makes it sensitive to any filtration-related procedure. Third, we show that, despite the non-optimized nature of the imaging prototype used, we can perform a full angular scan at acceptable dose levels and with exposure times not excessively distant from what is required by clinical practice. Finally, we discuss how the proposed phase contrast method, unlike other approaches apart from free-space propagation (which however requires a smaller focal spot, thus reducing the flux and increasing exposure times), can be easily implemented in a tomosynthesis geometry suitable for clinical use. In summary, we find that these technical results indicate a high potential for the combination of the two methods. Combining slice separation with detail enhancement provided by phase effects would substantially increase the detectability of small lesions and/or calcifications, which we aim to demonstrate in the next steps of this study.

A LABORATORY-BASED X-RAY PHASE CONTRAST IMAGING SCANNER WITH APPLICATIONS IN BIOMEDICAL AND NON-MEDICAL DISCIPLINES

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 extends it to large fields of view. This is based on X-ray sources and detectors available off the shelf, and its use has led to impressive results in mammography, cartilage imaging, testing of composite materials and security inspection. This article presents the method and the scanner prototype, and reviews its applications in selected biomedical and non-medical disciplines.

Sensitivity of laboratory based implementations of edge illumination X-ray phase-contrast imaging

We present a theoretical and experimental analysis of the angular sensitivity of edge illumination X-ray phase-contrast imaging in its implementation with conventional X-ray sources (sometimes referred to as the “coded-aperture” method). We study how the polychromaticity and finite source dimensions encountered in laboratory-based setups affect the detected signal. We also show that the sensitivity is independent of the period of the masks. Experimental images are presented and analyzed, proving that, despite the simple setup, high angular resolutions of a few hundred nanoradians can be obtained.