Asymmetric masks for laboratory-based X-ray phase-contrast imaging with edge illumination

We report on an asymmetric mask concept that enables X-ray phase contrast imaging without requiring any movement in the system during data acquisition. The method is compatible with laboratory equipment, namely a commercial detector and a rotating anode tube. The only motion required is that of the object under investigation which is scanned through the imaging system. Two proof-of-principle optical elements were designed, fabricated and experimentally tested. Quantitative measurements on samples of known shape and composition were compared to theory with good agreement. The method is capable of measuring the attenuation, refraction and (ultra-small-angle) X-ray scattering, does not have coherence requirements and naturally adapts to all those situations in which the X-ray image is obtained by scanning a sample through the imaging system

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

A laboratory based edge-Illumination x-ray phase-contrast imaging setup with two-directional sensitivity

We report on a preliminary laboratory based x-ray phase-contrast imaging system capable of achieving two directional phase sensitivity thanks to the use of L-shaped apertures. We show that in addition to apparent absorption, two-directional differential phase images of an object can be quantitatively retrieved by using only three input images. We also verify that knowledge of the phase derivatives along both directions allows for straightforward phase integration with no streak artefacts, a known problem common to all differential phase techniques. In addition, an analytical method for 2-directional dark field retrieval is proposed and experimentally demonstrated

Applications of a non-interferometric x-ray phase contrast imaging method with both synchrotron and conventional sources

We have developed a totally incoherent, non-interferometric x-ray phase contrast imaging (XPCI) method. This is based on the edge illumination (EI) concept developed at the ELETTRA synchrotron in Italy in the late ‘90s. The method was subsequently adapted to the divergent beam generated by a conventional source, by replicating it for every detector line through suitable masks. The method was modelled both with the simplified ray-tracing and with the more rigorous wave-optics approach, and in both cases excellent agreement with the experimental results was found. The wave-optics model enabled assessing the methods’ coherence requirements, showing that they are at least an order of magnitude more relaxed than in other methods, without this having negative consequences on the phase sensitivity. Our masks have large pitches (up to 50 times larger than in grating interferometry, for example), which allows for manufacturing through standard lithography, scalability, cost-effectiveness and easiness to align. When applied to a polychromatic and divergent beam generated by a conventional source, the method enables the detection of strong phase effects also with uncollimated, unapertured sources with focal spots of up to 100 mm, compatible with the state-of-the-art in mammography. When used at synchrotrons, it enables a contrast increase of orders of magnitude over other methods. Robust phase retrieval was proven for both coherent and incoherent sources, and additional advantages are compatibility with high x-ray energies and easy implementation of phase sensitivity in two directions simultaneously. This paper briefly summarizes these achievements and reviews some of the key results

Laboratory-based edge-illumination phase-contrast imaging: Dark-field retrieval and high-resolution implementations

Edge illumination is an X-ray phase-contrast imaging technique capable of quantitative retrieval of phase and amplitude images. The retrieval of the ultra-small-angle X-ray scattering was recently developed and implemented with the area-imaging counterpart of an edge-illumination system, sometimes referred to as coded-aperture setup. This is an incoherent and achromatic technique, well suited for translation of the potential of X-ray phase contrast imaging into efficient laboratory-scale setups. We report on recent advances of these developments along two main directions. One relates to the expansion of the technique with respect to the data analysis and corrections that are required when non-ideal optical elements are used and optimized sampling strategies. The second is directed towards high-resolution and high-energy implementations. A laboratory-based prototype for high-energy X-ray phase-contrast microscopy was built and its performance was modelled and experimentally characterized

Monte Carlo model of a polychromatic laboratory based edge illumination x-ray phase contrast system

A Monte Carlo model of a polychromatic laboratory based (coded aperture) edge illumination xray phase contrast imaging system has been developed and validated against experimental data. The ability for the simulation framework to be used to model two-dimensional images is also shown. The Monte Carlo model has been developed using the McXtrace engine and is polychromatic, i.e., results are obtained through the use of the full x-ray spectrum rather than an effective energy. This type of simulation can in future be used to model imaging of objects with complex geometry, for system prototyping, as well as providing a first step towards the development of a simulation for modelling dose delivery as a part of translating the imaging technique for use in clinical environments

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

Simultaneous implementation of low dose and high sensitivity capabilities in differential phase contrast and dark-field imaging with laboratory x-ray sources

We present a development of the laboratory-based implementation of edge-illumination (EI) x-ray phase contrast imaging (XPCI) that simultaneously enables low-dose and high sensitivity. Lab-based EI-XPCI simplifies the set-up with respect to other methods, as it only requires two optical elements, the large pitch of which relaxes the alignment requirements. Albeit in the past it was erroneously assumed that this would reduce the sensitivity, we demonstrate quantitatively that this is not the case. We discuss a system where the pre-sample mask open fraction is smaller than 50%, and a large fraction of the created beamlets hits the apertures in the detector mask. This ensures that the majority of photons traversing the sample are detected i.e. used for image formation, optimizing dose delivery. We show that the sensitivity depends on the dimension of the part of each beamlet hitting the detector apertures, optimized in the system design. We also show that the aperture pitch does not influence the sensitivity. Compared to previous implementations, we only reduced the beamlet fraction hitting the absorbing septa on the detector mask, not the one falling inside the apertures: the same number of x-rays per second is thus detected, i.e. the dose is reduced, but not at the expense of exposure time. We also present an extension of our phase-retrieval algorithm enabling the extraction of ultra-small-angle scattering by means of only one additional frame, with all three frames acquired within dose limits imposed by e.g. clinical mammography, and easy adaptation to lab-based phase-contrast x-ray microscopy implementations

Edge illumination and coded-aperture X-ray phase-contrast imaging: Increased sensitivity at synchrotrons and lab-based translations into medicine, biology and materials science

The edge illumination principle was first proposed at Elettra (Italy) in the late nineties, as an alternative method for achieving high phase sensitivity with a very simple and flexible set-up, and has since been under continuous development in the radiation physics group at UCL. Edge illumination allows overcoming most of the limitations of other phase-contrast techniques, enabling their translation into a laboratory environment. It is relatively insensitive to mechanical and thermal instabilities and it can be adapted to the divergent and polychromatic beams provided by X-ray tubes. This method has been demonstrated to work efficiently with source sizes up to 100m, compatible with state-of-the-art mammography sources. Two full prototypes have been built and are operational at UCL. Recent activity focused on applications such as breast and cartilage imaging, homeland security and detection of defects in composite materials. New methods such as phase retrieval, tomosynthesis and computed tomography algorithms are currently being theoretically and experimentally investigated. These results strongly indicate the technique as an extremely powerful and versatile tool for X-ray imaging in a wide range of applications

Quantification of microbubble concentration through x-ray phase contrast imaging

The use of microbubbles as a contrast agent for x-ray phase contrast imaging could both transform x-ray imaging into a “functional” modality and enable much needed monitoring of targeted drug delivery. To realize these benefits, it is essential to be able to quantify bubble concentration in a given tissue volume. We developed and validated a model that enables this to be achieved not only for phase-retrieved images obtained by processing multiple frames but also on “single-shot” images, a likely necessity in in-vivo implementations. Our experimental validation was based on analyzer-based imaging, but extension to other phase-based modalities is straightforward