Jinchuan Guo

Non-absorption grating approach for X-ray phase contrast imaging

We demonstrate a non-absorption grating approach for X-ray phase contrast imaging based-on grating interferometry. This technique overcomes the limitations imposed by absorption gratings, provides another choice for X-ray phase contrast imaging and potentially improves the image quality for higher X-ray photon energies. We constructed the key devices, established the system and obtained phase contrast images with a field of view larger than 5 centimeters, which is the limitation imposed by the size of our current CCD detector. This method has no need for absorption gratings, which represents a significant development for future promising applications in medicine and industry.

Fabrication of x-ray absorption gratings via micro-casting for grating-based phase contrast imaging

Grating-based x-ray differential phase contrast (DPC) imaging has shown huge potential. For broad applications, it is essential that the key components are low-cost, especially the absorption gratings. We therefore proposed and developed a micro-casting process for fabricating x-ray absorption gratings with bismuth. This process is feasible for mass production at low cost, with a large format, and a high aspect ratio. To develop this kind of absorption grating, an array with deep trenches was fabricated by photo-assisted electrochemical etching in a silicon wafer. The trenches were then filled with bubble-free, molten bismuth via capillary action and surface tension. Bismuth was attractive as a filling material because of its great mass absorption coefficient, low cost and broad environmental compatibility. Furthermore, our micro-casting process provided bismuth absorption gratings with a clean surface and no need for post treatment. To test their performance in x-ray DPC imaging, two bismuth absorption gratings, one as a periodic source and another as the analyzer, were used with periods of 42 and 3 µm and depths of 110 and 150 µm, respectively. The acquired phase-contrast images demonstrated that the micro-casting process produces qualified gratings for x-ray DPC imaging.

Sampling grating approach for X-ray differential phase contrast imaging

Grating-based X-ray differential phase contrast imaging (GDPCI) typically employs the phase-stepping technique to extract an objects phase information. This method requires heavy radiation dosage and is time consuming. Another potential approach is the reverse projection (RP) method, which, however, relies on a synchrotron radiation source to obtain highly sensitive differential phase contrast(DPC) signal. Here, we present an alternative approach that enables the RP method to be used with a conventional X-ray source and substantially improves the sensitivity of the DPC signal by replacing the analyzer grating of the GDPCI with a sampling grating. This development represents a significant step towards obtaining fast and low-dosage DPC images in medical, biological, and industrial applications.

Improvement of filling bismuth for x-ray absorption gratings through the enhancement of wettability

Filling materials with high x-ray linear absorption coefficients in high aspect-ratio (HAR) structures is a key process for the fabrication of absorption gratings used in x-ray differential phase-contrast imaging. Bismuth has been chosen as an effective filling material in micro-casting technology, because of its low cost both in price and facility use. However, repellence on structure surfaces against molten bismuth leads to an obstacle in terms of completely filling bismuth into the small-aperture and HAR microstructure formed by photo-assisted electrochemical etching in 5 inch silicon wafers. We propose and implement a novel method of surface modification to completely fill bismuth into these structures with periods of 3 μm and 42 μm, respectively, and as deep as 150 μm. The modified surface with a Bi2O3 layer covering the structure surface, including the side walls, induces an enhanced bismuth filling ratio. The superiority of the method is demonstrated by micrographs which show filled microstructures compared to the previously used method, where only a layer of 100 nm SiO2 was covered. Furthermore, we have observed that the improved micro-casting makes the absorption gratings clean surfaces, and no post treatment is needed.

Development of key devices of grating-based x-ray phase-contrast imaging technology at Shenzhen University

In this paper, the advance in the key devices of grating-based x-ray phase-contrast imaging technique, including a new x-ray tube, an x-ray phase grating, and an x-ray image detector assembly of dual function, has been introduced at Shenzhen University. A Talbot-effect-based imaging system consisted of these devices has been built up, in which there is only a phase grating without any absorption grating. Some small samples have been imaged on the system and their differential phase contrast images have been obtained. The simplification of the system can be favorable to the application progress of the grating-based x-ray imaging technology in the future.

Simple phase extraction in X-ray differential phase contrast imaging

A fast and simple method to extract phase-contrast images from interferograms is proposed, and its effectiveness is demonstrated through simulation and experiment. For x-ray differential phase contrast imaging, a strong attenuation signal acts as an overwhelming background intensity that obscures the weak phase signal so that no obvious phase-gradient information is detectable in the raw image. By subtracting one interferogram from another, chosen at particular intervals, the phase signal can be isolated and magnified.

Application of Bi Absorption Gratings in Grating-Based X-ray Phase Contrast Imaging

Among X-ray phase-contrast techniques, grating-based X-ray differential phase contrast (DPC) imaging using conventional X-ray tube sources is the most prominent one for widespread applications in the case of acquisition of high-quality absorption gratings in mass production. In this letter, we report on a new type of absorption grating made from Bi and manufactured by a micro-casting process. We tested Bi absorption gratings with our X-ray DPC imaging system and obtained high-quality phase-contrast images. Our efforts towards the practical application of X-ray DPC imaging are briefly outlined.

A sort of pulsed microfocal x-ray source

A sort of pulsed microfocus x-ray source has been theoretically and experimentally studied. The portable x-ray source is composed of three portions: LaB6 crystal cathode electron gun emitting system, electrostatic focusing system, and metal target system. The electrons are emitted form the hot crystal cathode, and controlled by modulated Wehnelt grid bias value and the ratio Dw/H, and concentrated by two-equal-radius-cylinder-electrodes focusing system. The x-ray photons are irradiated by high energy electron beam bombarding metal target. The new x-ray sources general-purpose capabilities such as pulsed radiation, focal spot size and luminance were preliminary tested. When the temperature of LaB6 cathode is about 1900K and partial pressures being kept below 10-7 torr, the minimal focus diameter is merely about 10 microns with the pulse width 65ms.

A low cost method for hard x-ray grating interferometry

Grating interferometry is advantageous over conventional x-ray absorption imaging because it enables the detection of samples constituted by low atomic number elements (low-Z materials). Therefore, it has a potential application in biological science and medical diagnostics. The grating interferometry has some critical optics components such as absorption gratings which are conventionally manufactured by the lithography, electroplating, and molding (LIGA) technique and employing gold as the absorbent material in it. However, great challenge lies in its implementations for practical applications because of the cost and difficulty to achieve high aspect ratio absorbing grating devices. In this paper, we present a low-cost approach that involves using the micro-casting technique with bismuth (Bi) as the absorber in source grating and as well as filling cesium iodide thallium(CsI:Tl) in a periodically structured scintillator. No costly facilities as synchrotron radiation are required and cheap material is used in our approach. Our experiment using these components shows high quality complementary images can be obtained with contrast of absorption, phase and visibility. This alternative method conquers the limitation of costly grating devices for a long time and stands an important step towards the further practical application of grating interferometry.

Quantitative analysis of fringe visibility in grating-based x-ray phase-contrast imaging

The newly developed x-ray differential phase-contrast imaging technique has attracted increasing research interest. In this study, we quantitatively analyze the fringe visibility obtained in differential phase-contrast imaging. Numerical results of the visibility for polychromatic x rays with different structure heights of absorption gratings are shown and discussed. Furthermore, the fringe visibility of the nonabsorption grating approach is calculated, and based on the results, we conclude that this approach can potentially be applied for higher x-ray photon energies. These analytic results will be useful for designing a differential phase-contrast imaging system for different applications.