Talbot-Lau Interferometry Research Articles

Experimental Realisation of High-sensitivity Laboratory X-ray Grating-based Phase-contrast Computed Tomography.

The possibility to perform high-sensitivity X-ray phase-contrast imaging with laboratory grating-based phase-contrast computed tomography (gbPC-CT) setups is of great interest for a broad range of high-resolution biomedical applications. However, achieving high sensitivity with laboratory gbPC-CT setups still poses a challenge because several factors such as the reduced flux, the polychromaticity of the spectrum, and the limited coherence of the X-ray source reduce the performance of laboratory gbPC-CT in comparison to gbPC-CT at synchrotron facilities. In this work, we present our laboratory X-ray Talbot-Lau interferometry setup operating at 40 kVp and describe how we achieve the high sensitivity yet unrivalled by any other laboratory X-ray phase-contrast technique. We provide the angular sensitivity expressed via the minimum resolvable refraction angle both in theory and experiment, and compare our data with other differential phase-contrast setups. Furthermore, we show that the good stability of our high-sensitivity setup allows for tomographic scans, by which even the electron density can be retrieved quantitatively as has been demonstrated in several preclinical studies.

Correction of data truncation artifacts in differential phase contrast (DPC) tomosynthesis imaging

The use of grating based Talbot–Lau interferometry permits the acquisition of differential phase contrast (DPC) imaging with a conventional medical x-ray source and detector. However, due to the limited area of the gratings, limited area of the detector, or both, data truncation image artifacts are often observed in tomographic DPC acquisitions and reconstructions, such as tomosynthesis (limited-angle tomography). When data are truncated in the conventional x-ray absorption tomosynthesis imaging, a variety of methods have been developed to mitigate the truncation artifacts. However, the same strategies used to mitigate absorption truncation artifacts do not yield satisfactory reconstruction results in DPC tomosynthesis reconstruction. In this work, several new methods have been proposed to mitigate data truncation artifacts in a DPC tomosynthesis system. The proposed methods have been validated using experimental data of a mammography accreditation phantom, a bovine udder, as well as several human cadaver breast specimens using a bench-top DPC imaging system at our facility.

Refined model for Talbot–Lau matter-wave optics with pulsed photodepletion gratings

We analyze time-domain Talbot–Lau interferometry of organic cluster beams that are exposed to pulsed photodepletion gratings in the vacuum ultraviolet. We focus particularly on the analysis of the complex (phase and absorption) character of the optical elements. The discussion includes the role of wavefront distortions due to mirror imperfections on the nanometer level and the effect of finite coherence in the diffraction gratings. This improved understanding of the interferometer allows us to extract new information on optical properties of anthracene and ferrocene clusters and to define conditions for future matter-wave experiments.

Dark-field X-ray imaging of unsaturated water transport in porous materials

We introduce in this Letter an approach to X-ray imaging of unsaturated water transport in porous materials based upon the intrinsic X-ray scattering produced by the material microstructural heterogeneity at a length scale below the imaging system spatial resolution. The basic principle for image contrast creation consists in a reduction of such scattering by permeation of the porosity by water. The implementation of the approach is based upon X-ray dark-field imaging via Talbot-Lau interferometry. The proof-of-concept is provided by performing laboratory-scale dark-field X-ray radiography of mortar samples during a water capillary uptake experiment. The results suggest that the proposed approach to visualizing unsaturated water transport in porous materials is complementary to neutron and magnetic resonance imaging and alternative to standard X-ray imaging, the latter requiring the use of contrast agents because based upon X-ray attenuation only.

Large-angle x-ray scatter in Talbot–Lau interferometry for breast imaging

Monte Carlo simulations were used to investigate large-angle x-ray scatter at design energy of 25 keV during small field of view (9.6 cm × 5 cm) differential phase contrast imaging of the breast using Talbot–Lau interferometry. Homogenous, adipose and fibroglandular breasts of uniform thickness ranging from 2 to 8 cm encompassing the field of view were modeled. Theoretically determined transmission efficiencies of the gratings were used to validate the Monte Carlo simulations, followed by simulations to determine the x-ray scatter reaching the detector. The recorded x-ray scatter was classified into x-ray photons that underwent at least one Compton interaction (incoherent scatter) and Rayleigh interaction alone (coherent scatter) for further analysis. Monte Carlo based estimates of transmission efficiencies showed good correspondence with theoretical estimates. Scatter-to-primary ratio increased with increasing breast thickness, ranging from 0.11 to 0.22 for 2–8 cm thick adipose breasts and from 0.12 to 0.28 for 2–8 cm thick fibroglandular breasts. The analyzer grating reduced incoherent scatter by ~18% for 2 cm thick adipose breast and by ~35% for 8 cm thick fibroglandular breast. Coherent scatter was the dominant contributor to the total scatter. Coherent-to-incoherent scatter ratio ranged from 2.2 to 3.1 for 2–8 cm thick adipose breasts and from 2.7 to 3.4 for 2–8 cm thick fibroglandular breasts.

Simulation framework for coherent and incoherent X-ray imaging and its application in Talbot-Lau dark-field imaging.

A simulation framework for coherent X-ray imaging, based on scalar diffraction theory, is presented. It contains a core C++ library and an additional Python interface. A workflow is presented to include contributions of inelastic scattering obtained with Monte-Carlo methods. X-ray Talbot-Lau interferometry is the primary focus of the framework. Simulations are in agreement with measurements obtained with such an interferometer. Especially, the dark-field signal of densely packed PMMA microspheres is predicted. A realistic modeling of the microsphere distribution, which is necessary for correct results, is presented. The framework can be used for both setup design and optimization but also to test and improve reconstruction methods.

Simulation of dark-field imaging of micro-calcifications in human breast tissue with X-ray Talbot-Lau interferometry

A simulation of dark-field imaging of sub-resolution structures with X-ray Talbot-Lau interferometry is presented. Data obtained from the simulation shows good agreement to a signal found in the dark-field image of a surgically removed sample of human breast tissue containing micro calcifications. A measure for the type of micro calcifications is introduced which can be calculated from dark-field signals. In a further analysis of the simulated data, it can be shown that the measure can be used to discriminate between different calcifications types.

Sparse phase-stepping in two-dimensional x-ray phase contrast imaging.

We have developed a sparse phase-stepping (SPS) method for x-ray Talbot-Lau interferometry, which first constructs a SPS intensity pattern of fewer images than the conventional phase-stepping (PS) method and then fills the data gap with neighboring pixels for phase retrieval. The SPS method is highly beneficial in practice since the fundamental difference in spatial resolution between the SPS and PS methods becomes negligible due to the blur caused by an interferometer. The concept of the SPS method has been proved by the experiment using a small effective source size. Furthermore, the experiment using a large effective source size has verified that in practical situations the SPS method can reduce the required number of images for phase retrieval and still offer the retrieved images with as high a spatial resolution as the PS method.

Developments of X-Ray Grating Imaging Technology

The present paper reviews the X-ray grating imaging systems at home and abroad from the aspects of technological characterizations and the newest researching focus. First, not only the imaging principles and the frameworks of the typical X-ray grating imaging system based on Talbot-Lau interferometry method, but also the algorithms of retrieving the signals of attenuation, refraction and small-angle scattering are introduced. Second, the system optimizing methods are discussed, which involves mainly the relaxing the requirement of high positioning resolution and strict circumstances for gratings and designing large field of view with high resolution. Third, two and four-dimensional grating-based X-ray imaging techniques are introduced.

Deformation quantization: Quantum mechanics lives and works in phase space

Wigner’s 1932 quasi-probability Distribution Function in phase-space, his first paper in English, is a special (Weyl) representation of the density matrix. It has been useful in describing quantum flows in semiclassical limits; quantum optics; nuclear and physics; decoherence (eg, quantum computing); quantum chaos; “Welcher Weg” puzzles; molecular Talbot–Lau interferometry; atomic measurements. It is further of great importance in signal processing (time-frequency analysis).Nevertheless, a remarkable aspect of its internal logic, pioneered by H. Groenewold and J. Moyal, has only blossomed in the last quarter-century: It furnishes a third, alternate, formulation of Quantum Mechanics, independent of the conventional Hilbert Space (the gold medal), or Path Integral (the silver medal) formulations, and perhaps more intuitive, since it shares language with classical mechanics: one need not choose sides between coordinate or momentum space variables, since it is formulated simultaneously in terms of position and momentum.This bronze medal formulation is logically complete and self-standing, and accommodates the uncertainty principle in an unexpected manner, so that it offers unique insights into the classical limit of quantum theory. The observables in this formulation are cnumber functions in phase space instead of operators, with the same interpretation as their classical counterparts, only now composed together in novel algebraic ways using star products .One might then envision an imaginary world in which this formulation of quantum mechanics had preceded the conventional Hilbert-space formulation, and its own techniques and methods had arisen independently, perhaps out of generalizations of classical mechanics and statistical mechanics.A sampling of such intriguing techniques and methods has already been published in C. K. Zachos, Int Jou Mod Phys A17 297-316 (2002), and T. L. Curtright, D. B. Fairlie, and C. K. Zachos, A Concise Treatise on Quantum Mechanics in Phase Space , (Imperial Press & World Scientific, 2014).

Cadaveric and in vivo human joint imaging based on differential phase contrast by X-ray Talbot-Lau interferometry

We developed an X-ray phase imaging system based on Talbot-Lau interferometry and studied its feasibility for clinical diagnoses of joint diseases. The system consists of three X-ray gratings, a conventional X-ray tube, an object holder, an X-ray image sensor, and a computer for image processing. The joints of human cadavers and healthy volunteers were imaged, and the results indicated sufficient sensitivity to cartilage, suggesting medical significance.

Partial coherence theory for x-ray phase contrast imaging technique with gratings

The partial coherence theory is applied to study the x-ray Talbot-Lau interferometry for phase contrast imaging with extended and polychromatic sources. Under a geometric condition for grating periods and distances between gratings, moiré fringes at the analyzer grating can be the same as the case of using one single slit. Although this geometric condition has been proposed before, we provide a quantitative explanation of the geometric condition compared to previous heuristic understanding. We then investigate the fringe visibility at the analyzer grating. For quasi-monochromatic sources, we derive an analytical formula and demonstrate that the visibility can reach 100% if the duty cycle of the source grating is less than an explicitly given bound. For polychromatic sources, we conduct numerical simulations to show that the visibility could reach near 100%. Both 1D- and 2D-grating systems are studied in this manuscript, respectively. Further work is to evaluate the theoretical results with physical experiments and establish design criteria for Talbot-Lau interferometers.

Phase-space tomography of matter-wave diffraction in the Talbot regime

We report on the theoretical investigation of the Wigner distribution function (WDF) reconstruction of the motional quantum state of large molecules in de Broglie interference. de Broglie interference of fullerenes and the like already proves the wavelike behaviour of these heavy particles, while we aim to extract more quantitative information about the superposition quantum state in motion. We simulate the reconstruction of the WDF numerically based on an analytic probability distribution and investigate its properties by the variation of parameters which are relevant for the experiment. Even though the WDF described in the near-field experiment cannot be reconstructed completely, we observe negativity even in the partially reconstructed WDF. We further consider incoherent factors to simulate the experimental situation, such as a finite number of slits, collimation and particle-slit van der Waals interaction. From this we find experimental conditions to reconstruct the WDF from Talbot interference fringes in molecule Talbot–Lau interferometry.

Multicontrast x-ray computed tomography imaging using Talbot-Lau interferometry without phase stepping

The purpose of this work is to demonstrate that multicontrast computed tomography (CT) imaging can be performed using a Talbot-Lau interferometer without phase stepping, thus allowing for an acquisition scheme like that used for standard absorption CT. Rather than using phase stepping to extract refraction, small-angle scattering (SAS), and absorption signals, the two gratings of a Talbot-Lau interferometer were rotated slightly to generate a moiré pattern on the detector. A Fourier analysis of the moiré pattern was performed to obtain separate projection images of each of the three contrast signals, all from the same single-shot of x-ray exposure. After the signals were extracted from the detector data for all view angles, image reconstruction was performed to obtain absorption, refraction, and SAS CT images. A physical phantom was scanned to validate the proposed data acquisition method. The results were compared with a phantom scan using the standard phase stepping approach. The reconstruction of each contrast mechanism produced the expected results. Signal levels and contrasts match those obtained using the phase stepping technique. Absorption, refraction, and SAS CT imaging can be achieved using the Talbot-Lau interferometer without the additional overhead of long scan time and phase stepping.

実用X線管を用いたX線格子干渉計の試み ―タルボ・ロー干渉計の医用画像への適用―

実用X線管を用いたX線格子干渉計の試み ―タルボ・ロー干渉計の医用画像への適用―

Talbot-Lau x-ray interferometry for high energy density plasma diagnostic

High resolution density diagnostics are difficult in high energy density laboratory plasmas (HEDLP) experiments due to the scarcity of probes that can penetrate above solid density plasmas. Hard x-rays are one possible probe for such dense plasmas. We study the possibility of applying an x-ray method recently developed for medical imaging, differential phase-contrast with Talbot-Lau interferometers, for the diagnostic of electron density and small-scale hydrodynamic instabilities in HEDLP experiments. The Talbot method uses micro-periodic gratings to measure the refraction and ultra-small angle scatter of x-rays through an object and is attractive for HEDLP diagnostic due to its capability to work with incoherent and polychromatic x-ray sources such as the laser driven backlighters used for HEDLP radiography. Our paper studies the potential of the Talbot method for HEDLP diagnostic, its adaptation to the HEDLP environment, and its extension of high x-ray energy using micro-periodic mirrors. The analysis is illustrated with experimental results obtained using a laboratory Talbot interferometer.

Theory and experimental verification of Kapitza–Dirac–Talbot–Lau interferometry

Kapitza–Dirac–Talbot–Lau interferometry (KDTLI) has recently been established for demonstrating the quantum wave nature of large molecules. A phase space treatment permits us to derive closed equations for the near-field interference pattern, as well as for the moiré-type pattern that would arise if the molecules were to be treated as classical particles. The model provides a simple and elegant way to account for the molecular phase shifts related to the optical dipole potential as well as for the incoherent effect of photon absorption at the second grating. We present experimental results for different molecular masses, polarizabilities and absorption cross sections using fullerenes and fluorofullerenes and discuss the alignment requirements. Our results with C60 and C70, C60F36 and C60F48 verify the theoretical description to a high degree of precision.

Sensitivity of X-ray Phase Imaging Based on Talbot Interferometry

The sensitivity of X-ray phase imaging based on Talbot interferometry is discussed. In order to evaluate the superiority of the technique to the conventional absorption-contrast method, which relies on X-ray absorption, a criterion is proposed. An experimental result of X-ray phase imaging with a Talbot interferometer is compared with the criterion. The criterion is also available for X-ray phase imaging based on Talbot–Lau interferometry. The advantage of X-ray phase imaging based on Talbot(–Lau) interferometry is more prominent when smaller structures are observed with smaller pixels.

Theory of decoherence in a matter wave Talbot-Lau interferometer

We present a theoretical framework to describe the effects of decoherence on matter waves in Talbot-Lau interferometry. Using a Wigner description of the stationary beam the loss of interference contrast can be calculated in closed form. The formulation includes both the decohering coupling to the environment and the coherent interaction with the grating walls. It facilitates the quantitative distinction of genuine quantum interference from the expectations of classical mechanics. We provide realistic microscopic descriptions of the experimentally relevant interactions in terms of the bulk properties of the particles and show that the treatment is equivalent to solving the corresponding master equation in paraxial approximation.