X-ray Phase Imaging Research Articles

Distribution of unresolvable anisotropic microstructures revealed in visibility-contrast images using x-ray Talbot interferometry

X-ray Talbot interferometry has been widely used as a technique for x-ray phase imaging and tomography. We propose a method using this interferometry for mapping distribution of parameters characterizing anisotropic microstructures, which are typically of the order of $\ensuremath{\mu}\mathrm{m}$ in size and cannot be resolved by the imaging system, in a sample. The method uses reduction in fringe visibility, which is caused by such unresolvable microstructures, in moir\'e images obtained using an interferometer. We applied the method to a chloroprene rubber sponge sample, which exhibited uniaxial anisotropy of reduced visibility. We measured the dependencies of reduced visibility on both the Talbot order and the orientation of the sample and obtained maps of three parameters and their anisotropies that characterize the unresolvable anisotropic microstructures in the sample. The maps indicated that the anisotropy of the sample's visibility contrast mainly originated from the anisotropy of the microstructure elements' average size. Our method directly provides structural information on unresolvable microstructures in real space, which is only accessible through the ultra-small-angle x-ray scattering measurements in reciprocal space, and is expected to be broadly applied to material, biological, and medical sciences.

Four-dimensional X-ray phase tomography with Talbot interferometry and white synchrotron radiation: dynamic observation of a living worm

X-ray Talbot interferometry is attractive as a method for X-ray phase imaging and phase tomography for objects that weakly absorb X-rays. Because X-ray Talbot interferometry has the advantage that X-rays of a broad energy bandwidth can be used, high-speed X-ray phase imaging is possible with white synchrotron radiation. In this paper, we demonstrate time-resolved three-dimensional observation with X-ray Talbot interferometry (namely, four-dimensional X-ray phase tomography). Differential phase images, from which a phase tomogram was reconstructed, were obtained through the Fourier-transform method, unlike the phase-stepping method that requires several (at least three) moiré images to be measured sequentially in order to generate one differential phase image. We demonstrate dynamic observation of a living worm in three dimensions with a time resolution of 0.5 s, visualizing a drastic change in the respiratory tract.

Quadriwave lateral shearing interferometry in an achromatic and continuously self-imaging regime for future x-ray phase imaging

We present in this Letter a type of quadriwave lateral shearing interferometer for x-ray phase imaging. This device is based on a phase chessboard, and we take advantage of the large spectrum of the source to produce interferograms with a propagation-invariant contrast. Such a grating has been created for hard x-ray interferometry and experimentally tested on a synchrotron beamline at Soleil.

Quantitative x-ray differential-interference-contrast microscopy with independently adjustable bias and shear

We present a quantitative x-ray phase imaging method that can be readily implemented on existing x-ray microscopy facilities. This technique utilizes Fresnel zone plates both as imaging optical elements for magnification and as second-order grating structures for phase-shifting interferometry. By making high-resolution quantitative x-ray phase information widely available, we expect this work to have significant impact on nanoscale biological and material studies.

Low-dose, simple, and fast grating-based X-ray phase-contrast imaging

Phase sensitive X-ray imaging methods can provide substantially increased contrast over conventional absorption-based imaging and therefore new and otherwise inaccessible information. The use of gratings as optical elements in hard X-ray phase imaging overcomes some of the problems that have impaired the wider use of phase contrast in X-ray radiography and tomography. So far, to separate the phase information from other contributions detected with a grating interferometer, a phase-stepping approach has been considered, which implies the acquisition of multiple radiographic projections. Here we present an innovative, highly sensitive X-ray tomographic phase-contrast imaging approach based on grating interferometry, which extracts the phase-contrast signal without the need of phase stepping. Compared to the existing phase-stepping approach, the main advantages of this new method dubbed "reverse projection" are not only the significantly reduced delivered dose, without the degradation of the image quality, but also the much higher efficiency. The new technique sets the prerequisites for future fast and low-dose phase-contrast imaging methods, fundamental for imaging biological specimens and in vivo studies.

Fabrication of X-rays mask with carbon membrane for diffraction gratings

We have produced diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. These diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Therefore, we decided to use the X-rays lithography technique that used synchrotron radiation of the directivity for a manufacture process. The accuracy of the completed structure depends largely on the accuracy of the X-ray mask. In our group, a resin material is conventionally used for the membrane of large X-ray masks. However, X-ray masks comprising a resin membrane have the disadvantage that, after several cycles of X-ray exposure, they crease and sag due to X-ray-derived heat. As a substitute for the conventional resin membrane, we experimentally fabricated a new X-ray mask using a carbon wafer membrane. The newly fabricated X-ray mask was subjected to X-ray exposure experiment. We succeeded in making the structure body which was almost shape. And the experimental results verified that the new mask did not deteriorate even when used repeatedly, demonstrating that it was highly durable.

Hard-X-Ray Phase-Difference Microscopy Using a Fresnel Zone Plate and a Transmission Grating

Novel hard x-ray phase imaging microscopy that simply uses an objective and a transmission grating is described. The microscope generated an image that exhibited twin features of a sample with an opposite phase contrast having a separation of a specific distance. Furthermore, the twin features were processed to generate an image mapping the x-ray phase shift through a simple algorithm. The presence of the grating did not degrade the spatial resolution of the microscope. The sensitivity of our microscope to light elements was about 2 orders of magnitude higher than that of the absorption contrast microscope that was attained by simply removing the grating. Our method is attractive for easily appending a quantitative phase-sensitive mode to normal x-ray microscopies, and it has potentially broad applications in biology and material sciences.

X-ray phase tomography with a Talbot interferometer in combination with an X-ray imaging microscope

An X-ray Talbot interferometer was combined with an X-ray imaging microscope to generate differential phase contrast. X-ray phase tomography was attained based on the measurement of the differential phase shift using the fringe scanning method. Polymer blend samples were observed and phase separation structures were depicted. The spatial resolution was 1.3 μm in this test experiment, which will be easily improved by increasing the magnification.

High-speed X-ray phase imaging and X-ray phase tomography with Talbot interferometer and white synchrotron radiation

X-ray Talbot interferometry, which uses two transmission gratings, has the advantage that broad energy bandwidth x-rays can be used. We demonstrate the use of white synchrotron radiation for high-speed X-ray phase imaging and tomography in combination with an X-ray Talbot interferometer. The moiré fringe visibility over 20% was attained, enabling quantitative phase measurement. X-ray phase images with a frame rate of 500 f/s and an X-ray phase tomogram with a scan time of 0.5 s were obtained successfully. This result suggests a breakthrough for time-resolved three-dimensional observation of objects that weakly absorb X-rays, such as soft material and biological objects.

Grating-Based X-ray Phase Imaging Using Multiline X-ray Source

Differential phase-contrast X-ray imaging has been performed in a Talbot–Lau configuration, where a multiline X-ray source was used instead of a combination of a hard-X-ray multiple slit and a normal focus X-ray generator. When the multiple slit is used, a high aspect ratio structure is needed and slit width should be below 10 µm for its function. The fabrication and use of such a multislit can be omitted using the presented configuration. The multiline X-ray source was developed by making grooves on a tungsten rotating anode, which was irradiated by an electron beam to generate X-rays. An array of 10 µm line sources with a pitch of 30 µm was formed and combined with a 4.5 µm pitch phase grating and a 5.3 µm pitch amplitude grating to generate differential phase contrast. With a total exposure time of 40 s, a differential phase image depicting cartilages was obtained.

Fabrication of X-Ray Gratings Using X-Ray Lithography Technique for X-Ray Talbot Interferometer

The X-ray radiographic imaging technique is very important in medical, biological, inspection, material science, and other fields. However, it is not enough to obtain a clear X-ray image of samples with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phase-imaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required to have a narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricated high-aspect-ratio X-ray gratings with a pitch of , a height of , and a large effective area of using X-ray lithography and narrow electroforming techniques. In this paper, we discuss the fabrication process of X-ray gratings with a narrow pitch and high-aspect-ratio structure, and results of X-ray phase tomography using an X-ray Talbot interferometer with these X-ray gratings.

Fabrication of High Aspect Ratio X-ray Grating Using X-ray Lithography

X-ray radiographic imaging technique has found applications in various fields. However, it is not enough to get clear X-ray images of samples with low absorbance, such as biological soft tissues. To resolve this problem, we proposed a method using an X-ray Talbot interferometer of X-ray phase imaging. In this X-ray Talbot interferometer, X-ray gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we have developed and succeeded high aspect ratio X-ray gratings with a pitch of 5.3 μm and a height of 30 μm using X-ray lithography technique. We discuss that the X-ray gratings having a large effective area in order to obtain imaging size of practical use in medical application. In currently study, we have fabricated the X-ray gratings with a large effective area of 60 mm×60 mm. And, we conducted X-ray phase tomography of mouse at the chest and abdominal using X-ray Talbot interferometer. As a result, we successfully observed soft tissues and high density tissues. With the aim of broadening a field of view, we try to fabricate X-ray gratings that have a pitch of below 5.3 μm and larger area of 100 mm square. This result suggests that X-ray Talbot interferometer is a novel and simple method for phase sensitive X-ray radiography.

Feasibility study of the iterative x-ray phase retrieval algorithm

An iterative phase retrieval algorithm was previously investigated for in-line x-ray phase imaging. Through detailed theoretical analysis and computer simulations, we now discuss the limitations, robustness, and efficiency of the algorithm. The iterative algorithm was proved robust against imaging noise but sensitive to the variations of several system parameters. It is also efficient in terms of calculation time. It was shown that the algorithm can be applied to phase retrieval based on one phase-contrast image and one attenuation image, or two phase-contrast images; in both cases, the two images can be obtained either by one detector in two exposures, or by two detectors in only one exposure as in the dual-detector scheme.

Fabrication of X-ray Grating Using X-ray Lithography Technique

X-ray radiographic imaging technique is very important in medical, biological, inspection, material science, and so on. However, it is not enough to obtain clear X-ray images of samples with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phase imaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required to have narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricated high aspect ratio X-ray gratings with a pitch of 5.3 um, a height of 30 um, and a large effective area of 100 mm × 100 mm using X-ray lithography and narrow electroforming technique. In this paper, we discuss the fabrication process of X-ray gratings and results of X-ray phase tomography using an X-ray Talbot interferometer with these X-ray gratings.

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.

Fabrication of Multiple Slit Using Stacked-Sliced Method for Hard X-ray Talbot–Lau Interferometer

We propose using a multiple slit fabricated by a simple and economical stacked-sliced method for X-ray phase imaging with a Talbot–Lau X-ray interferometer. Foils of Ta and Al were stacked alternately, and the stack was sliced up perpendicular to the stacking direction. We successfully fabricated a hard X-ray multiple slit with a space size (Al foil thickness) of about 10 µm and an aspect ratio of 60. Optical microscopy evaluation showed its regular pitch pattern at its surface. A high-resolution X-ray transmission image proved the regularity of the inner part. The visibility of moiré fringes and the phase-contrast image obtained using the Talbot–Lau interferometer with the multiple slit proved the feasibility of the stacked-sliced approach.

Multiwavelength elemental contrast phase imaging by the use of dispersion effects

In many frontier areas of research it is the distribution of a particular element in the sample which is of crucial interest. This paper proposes a method in which the signal due to the presence of a particular element can be enhanced while signals due to other elements present in the sample are suppressed. Rather than comparing the images measured above and below an absorption edge in conventional absorption contrast technique this method enhances the phase effect due to a particular element by taking multiple-wavelength measurements in the vicinity of its absorption edge of the element of interest. It is shown that the method can be incorporated to various techniques of x-ray phase imaging and therefore promises to have a very wide range of applications.

X-ray phase radiography and tomography of soft tissue using grating interferometry

X-ray phase and absorption radiographs and tomograms of the heart of a rat were taken with an X-ray grating interferometer with monochromatic synchrotron radiation at a photon energy of 17.5 keV. The phase images show largely superior quality with respect to the absorption images taken with the same dose, particularly much better contrast and contrast-to-noise ratio. Different tissues can clearly be distinguished. The results demonstrate the potential of grating interferometry for two- and three-dimensional X-ray imaging of biological soft tissue in an aqueous environment.

Fabrication of large area diffraction grating using LIGA process

X-ray imaging is a very important technology in the fields of medical, biological, inspection, material science, etc. However, it is not enough to get the clear X-ray imaging with low absorbance. We have produced a diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. In this X-ray Talbot interferometer, diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we succeeded to fabricate a high aspect ratio diffraction grating with a pitch of 8 μm and small area using a deep X-ray lithography technique. We discuss that the diffraction gratings having a narrow pitch and an large effective area to obtain imaging size of practical use in medical application. If the pitch of diffraction gratings were narrow, it is expected high resolution imaging for X-ray Talbot interferometer. We succeeded and fabricated the diffraction grating with pitch of 5.3 μm, Au height of 28 μm and an effective area of 60 × 60 mm2.

High-resolution brain tumor visualization using three-dimensional x-ray phase contrast tomography

We report on significant advances and new results concerning a recently developed method for grating-based hard x-ray phase tomography. We demonstrate how the soft tissue sensitivity of the technique is increased and show in vitro tomographic images of a tumor bearing rat brain sample, without use of contrast agents. In particular, we observe that the brain tumor and the white and gray brain matter structure in a rat's cerebellum are clearly resolved. The results are potentially interesting from a clinical point of view, since a similar approach using three transmission gratings can be implemented with more readily available x-ray sources, such as standard x-ray tubes. Moreover, the results open the way to in vivo experiments in the near future.