Virtual edge illumination and one dimensional beam tracking for absorption, refraction, and scattering retrieval

We propose two different approaches to retrieve x-ray absorption, refraction, and scattering signals using a one dimensional scan and a high resolution detector. The first method can be easily implemented in existing procedures developed for edge illumination to retrieve absorption and refraction signals, giving comparable image quality while reducing exposure time and delivered dose. The second method tracks the variations of the beam intensity profile on the detector through a multi-Gaussian interpolation, allowing the additional retrieval of the scattering signal

A continuous sampling scheme for edge illumination x-ray phase contrast imaging

We discuss an alternative acquisition scheme for edge illumination (EI) x-ray phase contrast imaging (XPCi) based on a continuous scan of the object, and compare its performance to that of a previously used scheme, which involved scanning the object in discrete steps rather than continuously. By simulating signals for both continuous and discrete methods under realistic experimental conditions, the e ect of the spatial sampling rate is analysed with respect to metrics such as image contrast and accuracy of the retrieved phase shift. Experimental results con rm the theoretical predictions. Despite being limited to a speci c example, the results indicate that continuous schemes present advantageous features compared to discrete ones. Not only can they be used to speed up the acquisition, but they also prove superior in terms of accurate phase retrieval. The theory and experimental results provided in this study will guide the design of future EI experiments through the implementation of optimised acquisition schemes and sampling rates

Optimization of sensitivity, dose and spatial resolution in edge illumination X-ray phase-contrast imaging

Edge illumination (EI) X-ray phase-contrast imaging has great potential for applications in a wide range of research, industrial and clinical fields. The optimization of the EI experimental setup for a given application is therefore essential, in order to take full advantage of the capabilities of the technique. In this work, we analyze the dependence of the angular sensitivity, spatial resolution and dose delivered to the sample upon the various experimental parameters, and describe possible strategies to optimize them. The obtained results will be important for the design of future EI experimental setups, in particular enabling their tailoring to specific applications

Edge illumination X-ray phase tomography of multi-material samples using a single-image phase retrieval algorithm

In this paper we present a single-image phase retrieval algorithm for multi-material samples, developed for the edge illumination (EI) X-ray phase contrast imaging method. The theoretical derivation is provided, along with any assumptions made. The algorithm is evaluated quantitatively using both simulated and experimental results from a computed tomography (CT) scan using the EI laboratory implementation. Qualitative CT results are provided for a biological sample containing both bone and soft-tissue. Using a single EI image per projection and knowledge of the complex refractive index, the algorithm can accurately retrieve the interface between a given pair of materials. A composite CT slice can be created by splicing together multiple CT reconstructions, each retrieved for a different pair of materials

On the relative performance of edge illumination x-ray phase contrast CT and conventional, attenuation-based CT

Purpose This article is aimed at comparing edge illumination (EI) x-ray phase contrast computed tomography (PCT) and conventional (attenuation-based) computed tomography (CT), based on their respective contrast and noise transfer. Methods The noise in raw projections obtained with EI PCT is propagated through every step of the data processing, including phase retrieval and tomographic reconstruction, leading to a description of the noise in the reconstructed phase tomograms. This is compared to the noise in corresponding attenuation tomograms obtained with CT. Specifically, a formula is derived that allows evaluating the relative performance of both modalities on the basis of their contrast-to-noise ratio (CNR), for a variety of experimental parameters. Results The noise power spectra of phase tomograms are shifted towards lower spatial frequencies, leading to a fundamentally different noise texture. The relative performance of EI PCT and CT, in terms of their CNR, is linked to spatial resolution: the CNR in phase tomograms is generally superior to that in attenuation tomograms for higher spatial resolutions (tens to hundreds of μm), but inferior for lower spatial resolutions (hundreds of μm to mm). Conclusions These results imply that EI PCT could outperform CT in applications for which high spatial resolutions are key, i.e. small animal or specimen imaging. This article is protected by copyright. All rights reserved

The concept of contrast transfer function for edge illumination X-ray phase-contrast imaging and its comparison with the free-space propagation technique

Previous studies on edge illumination (EI) X-ray phase-contrast imaging (XPCi) have investigated the nature and amplitude of the signal provided by this technique. However, the response of the imaging system to different object spatial frequencies was never explicitly considered and studied. This is required in order to predict the performance of a given EI setup for different classes of objects. To this scope, in the present work we derive analytical expressions for the contrast transfer function of an EI imaging system, using the approximation of near-field regime, and study its dependence upon the main experimental parameters. We then exploit these results to compare the frequency response of an EI system with respect of that of a free-space propagation XPCi one. The results achieved in this work can be useful for predicting the signals obtainable for different types of objects and also as a basis for new retrieval methods

Theoretical comparison of three X-ray phase-contrast imaging techniques: propagation-based imaging, analyzer-based imaging and grating interferometry

Various X-ray phase-contrast imaging techniques have been developed and applied over the last twenty years in different domains, such as material sciences, biology and medicine. However, no comprehensive inter-comparison exists in the literature. We present here a theoretical study that compares three among the most used techniques: propagation-based imaging (PBI), analyzer-based imaging (ABI) and grating interferometry (GI). These techniques are evaluated in terms of signal-to-noise ratio, figure of merit and spatial resolution. Both area and edge signals are considered. Dependences upon the object properties (absorption, phase shift) and the experimental acquisition parameters (energy, system point-spread function etc.) are derived and discussed. The results obtained from this analysis can be used as the reference for determining the most suitable technique for a given application

Improved sensitivity at synchrotrons using edge illumination X-ray phase-contrast imaging

The application of the X-ray phase-contrast ‘edge illumination’ principle to the highly coherent beams available at synchrotron radiation facilities is presented here. We show that, in this configuration, the technique allows achieving unprecedented angular sensitivity, of the order of few nanoradians. The results are obtained at beamlines of two different synchrotron radiation facilities, using various experimental conditions. In particular, different detectors and X-ray energies (12 keV and 85 keV) were employed, proving the flexibility of the method and the broad range of conditions over which it can be applied. Furthermore, the quantitative separation of absorption and refraction information, and the application of the edge illumination principle in combination with computed tomography, are also demonstrated. Thanks to its extremely high phase sensitivity and its flexible applicability, this technique will both improve the image quality achievable with X-ray phase contrast imaging and allow tackling areas of application which remain unexplored until now

Large field of view, fast and low dose multimodal phase-contrast imaging at high x-ray energy

X-ray phase contrast imaging (XPCI) is an innovative imaging technique which extends the contrast capabilities of ‘conventional’ absorption based x-ray systems. However, so far all XPCI implementations have suffered from one or more of the following limitations: low x-ray energies, small field of view (FOV) and long acquisition times. Those limitations relegated XPCI to a ‘research-only’ technique with an uncertain future in terms of large scale, high impact applications. We recently succeeded in designing, realizing and testing an XPCI system, which achieves significant steps toward simultaneously overcoming these limitations. Our system combines, for the first time, large FOV, high energy and fast scanning. Importantly, it is capable of providing high image quality at low x-ray doses, compatible with or even below those currently used in medical imaging. This extends the use of XPCI to areas which were unpractical or even inaccessible to previous XPCI solutions. We expect this will enable a long overdue translation into application fields such as security screening, industrial inspections and large FOV medical radiography – all with the inherent advantages of the XPCI multimodality

Low-dose x-ray phase contrast tomography: Experimental setup, image reconstruction and applications in biomedicine

An unmet demand for high resolution tomographic imaging modalities providing enhanced soft tissue contrast exists in a number of biomedical disciplines. X-ray phase contrast imaging (XPCi) methods can provide a solution: contrast is driven by phase (refraction) effects rather than attenuation effects, the formers being much larger than the latters for weakly attenuating materials and energies typically used for biomedical imaging. However, the majority of the existing XPCi methods suffer from drawbacks affecting their implementation outside specialized facilities such as synchrotrons and therefore their applicability to biomedical research. The Edge Illumination (EI) XPCi method has the potential to overcome or at least mitigate most of these drawbacks. Its major strengths are its simple setup, compatibility with commercially available x-ray tubes and potential for low-dose imaging. EI XPCi has recently been implemented as a tomographic modality, and it was demonstrated that the method can provide quantitatively accurate volumetric images acquired with low entrance doses. This paper explains the experimental requirements for tomographic EI XPCi, outlines the image reconstruction process and discusses potential applications in biomedicine. As an example, first experimental images of an atherosclerotic plaque specimen are presented