Vincent Revol

Noise analysis of grating-based x-ray differential phase contrast imaging.

The sensitivity of x-ray radiographic images, meaning the minimal detectable change in the thickness or in the index of refraction of a sample, is directly related to the uncertainty of the measurement method. In the following work, we report on the recent development of quantitative descriptions for the stochastic error of grating-based differential phase contrast imaging (DPCi). Our model includes the noise transfer characteristics of the x-ray detector and the jitter of the phase steps. We find that the noise in DPCi depends strongly on the phase stepping visibility and the sample properties. The results are supported by experimental evidence acquired with our new instrument with a field of view of 50x70 mm(2). Our conclusions provide general guidelines to optimize grating interferometers for specific applications and problems.

Sub-pixel porosity revealed by x-ray scatter dark field imaging

X-ray scatter dark field imaging based on the Talbot-Lau interferometer allows for the measurement of ultra–small angle x-ray scattering. The latter is related to the variations in the electron density in the sample at the sub- and micron-scale. Therefore, information on features of the object below the detector resolution can be revealed. In this article, it is demonstrated that scatter dark field imaging is particularly adapted to the study of a material’s porosity. An interferometer, optimized for x-ray energies around 50 keV, enables the investigation of aluminum welding with conventional laboratory x-ray tubes. The results show an unprecedented contrast between the pool and the aluminum workpiece. Our conclusions are confirmed due to micro-tomographic three-dimensional reconstructions of the same object with a microscopic resolution.

Orientation-selective X-ray dark field imaging of ordered systems

X-ray scatter dark field imaging with a grating interferometer is becoming a standard tool for the characterization of microscopic texture of samples. Recently, it was shown that directional information could also be recovered when the sample displays an anisotropic ordering such as, for instance, a bundle of microscopic fibers. Here, we demonstrate that previously suggested approaches are ambiguous when multiple anisotropic orientations coexist in the sample. Therefore, we developed a new orientation-selective approach which allows for separating the contributions of individual orientations provided that these orientations are known a-priori. The method, demonstrated experimentally using a well-defined wood sample, is envisioned to be of high interest for the non-destructive inspection of composite materials.

Dual energy phase contrast x-ray imaging with Talbot-Lau interferometer

In weakly absorbing materials such as polymers and soft tissue, x-ray phase sensitive imaging methods can provide substantially enhanced contrast compared to classical, absorption based radiography. For specific applications, the latter can be applied in a dual energy scheme that helps to identify, discriminate and/or quantify materials. In this paper, we report on a new method that combines the idea of dual energy with x-ray phase contrast imaging and thus provides material sensitivity among poor absorbers. The dual energy modality cannot be applied in common phase contrast imaging schemes because of their demand for limited bandwidth or even monochromatic x-ray sources. Our new interferometric method based on diffraction gratings can overcome this shortcoming and thus simultaneously deliver x-ray phase contrast images for two distinct x-ray energy intervals. It has been shown that high quality images can be obtained with the dual energy phase setup. Energy spectra with 40 kV and 70 kV were applied to ob...

A new method for fusion, denoising and enhancement of x-ray images retrieved from Talbot-Lau grating interferometry

This paper introduces a new image denoising, fusion and enhancement framework for combining and optimal visualization of x-ray attenuation contrast (AC), differential phase contrast (DPC) and dark-field contrast (DFC) images retrieved from x-ray Talbot-Lau grating interferometry. The new image fusion framework comprises three steps: (i) denoising each input image (AC, DPC and DFC) through adaptive Wiener filtering, (ii) performing a two-step image fusion process based on the shift-invariant wavelet transform, i.e. first fusing the AC with the DPC image and then fusing the resulting image with the DFC image, and finally (iii) enhancing the fused image to obtain a final image using adaptive histogram equalization, adaptive sharpening and contrast optimization. Application examples are presented for two biological objects (a human tooth and a cherry) and the proposed method is compared to two recently published AC/DPC/DFC image processing techniques. In conclusion, the new framework for the processing of AC, DPC and DFC allows the most relevant features of all three images to be combined in one image while reducing the noise and enhancing adaptively the relevant image features. The newly developed framework may be used in technical and medical applications.

Design and performance of an ultra-flexible two-photon microscope for in vivo research

We present a cost-effective in vivo two-photon microscope with a highly flexible frontend for in vivo research. Our design ensures fast and reproducible access to the area of interest, including rotation of imaging plane, and maximizes space for auxiliary experimental equipment in the vicinity of the animal. Mechanical flexibility is achieved with large motorized linear stages that move the objective in the X, Y, and Z directions up to 130 mm. 360° rotation of the frontend (rotational freedom for one axis) is achieved with the combination of a motorized high precision bearing and gearing. Additionally, the modular design of the frontend, based on commercially available optomechanical parts, allows straightforward updates to future scanning technologies. The design exceeds the mobility of previous movable microscope designs while maintaining high optical performance.

Recent developments on X-ray phase contrast imaging technology at CSEM

X-ray phase contrast imaging (XPCi) using the Talbot-Lau grating interferometer attracts increasing attention for its implementation in various fields of applications such as in the (bio-) medical domain, non-destructive testing or security. Since the method is compatible with laboratory X-ray tube sources as well as with large field of view digital X-ray image sensors, it has a large potential to provide XPCi for industrial and medical applications as widespread as conventional X-raying is. Here, we report on our recent results and measurements regarding the grating interferometer technology.

Reduction of phase artifacts in differential phase contrast computed tomography

X-ray differential phase contrast computed tomography (DPC CT) with a Talbot-Lau interferometer setup allows visualizing the three-dimensional distribution of the refractive index by measuring the shifts of an interference pattern due to phase variations of the X-ray beam. Unfortunately, severe reconstruction artifacts appear in the presence of differential phase wrapping and clipping. In this paper, we propose to use the attenuation contrast, which is obtained from the same measurement, for correcting the DPC signal. Using the example of a DPC CT measurement with pronounced phase artifacts, we will discuss the efficiency of our phase artifact correction method.

PHASE SENSITIVE X‐RAY IMAGING: TOWARDS ITS INTERDISCIPLINARY APPLICATIONS

X‐ray phase imaging including phase tomography has been attracting increasing attention during the past few decades. The advantage of X‐ray phase imaging is that an extremely high sensitivity is achieved for weakly absorbing materials, such as biological soft tissues, which generate a poor contrast by conventional schemes. Especially for such living samples, where the reduction of the applied dose is of paramount interest, phase sensitive measurements schemes have an inherent potential for a significant dose reduction combined with an image quality enhancement. Several methods have been invented for x‐ray phase contrast imaging that either use an approach based on interferometry, diffraction or wave‐field propagation. Some of these techniques have a potential for commercial applications, such as in medicine, non‐destructive testing, security and inspection. The scope of this manuscript thus deals with one particular such technique that measures the diffraction caused by the specimen by means of a grating ...

EVITA project: Comparison Between Traditional Non-Destructive Techniques and Phase Contrast X-Ray Imaging applied to Aerospace Carbon Fibre Reinforced Polymer

The EU-project EVITA (Non-Destructive EValuation, Inspection and Testing of Primary Aeronautical Composite Structures Using Phase Contrast X-Ray Imaging) aims at bringing Grating-based Phase Contrast X-ray imaging technology to Non-Destructive Evaluation and Inspection of advanced primary and/or complex aerospace composite structures. Grating-based Phase Contrast X-Ray Imaging is based on the so-called Talbot-Lau interferometer, which is made of the combination of a standard X-ray apparatus with three transmission gratings as documented in the literature. This paper presents a comparison of two traditional non-destructive techniques (NDT): ultrasonic through transmission (immersed and water jet) and ultrasonic phased-array pulse echo, with the developed phase contrast X-Ray Imaging applied to advanced aerospace carbon fibre reinforced polymer. Typical defects produced during manufacture is examined as part of the testing and validation procedure. The following defects have been identified as being those most likely to be detected more effectively by the Grating-based Phase Contrast X-Ray Imaging process than other state of the art industrial NDT techniques: porosity, foreign objects, cracks, resin rich, cut fibres, and wavy fibres. The introduction of this innovative methodology is expected to provide the aeronautical industry with a reliable and detailed insight of the integrity of thin and thick composite structures as well as of complex geometry ones, such as integrated closed boxes and sandwiches.