One-Step Method for Material Quantitation Using In-Line Tomography With Single Scanning.

OBJECTIVE: Quantitative technique based on In-line phase-contrast computed tomography with single scanning attracts more attention in application due to the flexibility of the implementation. However, the quantitative results usually suffer from artifacts and noise since the phase retrieval and reconstruction are independent ("two-step") without feedback from the original data. The work aims to investigate a method for material quantitation to improve the image quality of In-line tomography within single scanning. METHOD: An iterative method based Fresnel diffraction imaging model is developed in this work, which directly reconstructs the refractive index decrement δ and imaginary ß of the object from observed data ("one-step"). Moreover, high-quality material decomposition results are obtained by using a linear approximation in the iterative process. RESULTS: Compared with the existing methods, Our method shows a higher peak signal-to-noise ratio and structural similarity in numerical experimental results. Additionally, the quantitation accuracy of the proposed method is greater than 97.2 % by calculating the equivalent atomic number of the decomposed basic material in the real experiment. CONCLUSION: We demonstrate that this one-step method greatly reduces noise and improves quantitative reconstruction and decomposition results. SIGNIFICANCE: This algorithm has the potential for quantitative imaging research using In-line tomography in future biomedical applications.

[Study on Parametric Release of Ethylene Oxide Sterilization of Medical Devices].

This study briefly introduces the basic theory of sterilization, the characteristics of ethylene oxide sterilization for medical devices and the key factors about sterilization effectiveness, analyzes and compares three methods used in the product release of medical devices sterilized by ethylene oxide: test for sterility, traditional release and parametric release, and focuses on the theoretical basis, feasibility, validation requirements, advantages and disadvantages of parametric release.

Angular sensitivity of an x-ray differential phase contrast imaging system with real and virtual source images.

In this work, a novel, to the best of our knowledge, approach based on an x-ray thin lens imaging theory is proposed to predict the angular sensitivity responses of dual-phase-grating differential phase contrast (DPC) interferometers. Experimental validations have been performed to demonstrate the high accuracy of theoretical predictions using two different setups: one with real source images and the other with virtual source images. This new sensitivity calculation method is helpful to optimize the DPC imaging performance of a dual-phase-grating system.

Generalized reverse projection method for grating-based phase tomography.

The reverse projection protocol results in fast phase-contrast imaging thanks to its compatibility with conventional computed-tomography scanning. Many researchers have proposed variants. However, all these reverse projection methods in grating-based phase-contrast imaging are built on the hypothesis of the synchronous phase of reference shifting curves in the whole field of view. The hypothesis imposes uniformity and alignment requirements on the gratings, thus the field of view is generally limited. In this paper, a generalized reverse projection method is presented analytically for the case of non-uniform reference in grating-based phase tomography. The method is demonstrated by theoretical derivation, numerical simulations and synchrotron radiation experiments. The influence of imaging position to sensitivity, and the phase-wrapping phenomenon are also discussed. The proposed method combines the advantages of the high efficiency of the reverse projection method and the universal applicability of the phase-stepping method. The authors believe that the method would be used widely in fast and dose-constrained imaging.

A method for material decomposition and quantification with grating based phase CT.

Material decomposition (MD) is an important application of computer tomography (CT). For phase contrast imaging, conventional MD methods are categorized into two types with respect to different operation sequences, i.e., "before" or "after" image reconstruction. Both categories come down to two-step methods, which have the problem of noise amplification. In this study, we incorporate both phase and absorption (PA) information into MD process, and correspondingly develop a simultaneous algebraic reconstruction technique (SART). The proposed method is referred to as phase & absorption material decomposition-SART (PAMD-SART). By iteratively solving an optimization problem, material composition and substance quantification are reconstructed directly from absorption and differential phase projections. Comparing with two-step MD, the proposed one-step method is superior in noise suppression and accurate decomposition. Numerical simulations and synchrotron radiation based experiments show that PAMD-SART outperforms the classical MD method (image-based and dual-energy CT iterative method), especially for the quantitative accuracy of material equivalent atomic number.

Dual phase grating based X-ray differential phase contrast imaging with source grating: theory and validation.

In this work, we developed a new theoretical framework using wave optics to explain the working mechanism of the grating based X-ray differential phase contrast imaging (XPCI) interferometer systems consist of more than one phase grating. Under the optical reversibility principle, the wave optics interpretation was simplified into the geometrical optics interpretation, in which the phase grating was treated as a thin lens. Moreover, it was derived that the period of an arrayed source, e.g., the period of a source grating, is always equal to the period of the diffraction fringe formed on the source plane. When a source grating is utilized, the theory indicated that it is better to keep the periods of the two phase gratings different to generate large period diffraction fringes. Experiments were performed to validate these theoretical findings.

Direct information retrieval after 3D reconstruction in grating-based X-ray phase-contrast computed tomography.

Grating-based X-ray differential phase-contrast imaging has attracted a great amount of attention and has been considered as a potential imaging method in clinical medicine because of its compatibility with the traditional X-ray tube source and the possibility of a large field of view. Moreover, phase-contrast computed tomography provides three-dimensional phase-contrast visualization. Generally, two-dimensional information retrieval performed on every projection is required prior to three-dimensional reconstruction in phase-contrast computed tomography. In this paper, a three-dimensional information retrieval method to separate absorption and phase information directly from two reconstructed images is derived. Theoretical derivations together with numerical simulations have been performed to confirm the feasibility and veracity of the proposed method. The advantages and limitations compared with the reverse projection method are also discussed. Owing to the reduced data size and the absence of a logarithm operation, the computational time for information retrieval is shortened by the proposed method. In addition, the hybrid three-dimensional images of absorption and phase information were reconstructed using an absorption reconstruction algorithm, hence the existing data pre-processing methods and iterative reconstruction algorithms in absorption reconstruction may be utilized in phase reconstruction immediately.

Angular signal radiography.

Microscopy techniques using visible photons, x-rays, neutrons, and electrons have made remarkable impact in many scientific disciplines. The microscopic data can often be expressed as the convolution of the spatial distribution of certain properties of the specimens and the inherent response function of the imaging system. The x-ray grating interferometer (XGI), which is sensitive to the deviation angle of the incoming x-rays, has attracted significant attention in the past years due to its capability in achieving x-ray phase contrast imaging with low brilliance source. However, the comprehensive and analytical theoretical framework is yet to be presented. Herein, we propose a theoretical framework termed angular signal radiography (ASR) to describe the imaging process of the XGI system in a classical, comprehensive and analytical manner. We demonstrated, by means of theoretical deduction and synchrotron based experiments, that the spatial distribution of specimens' physical properties, including absorption, refraction and scattering, can be extracted by ASR in XGI. Implementation of ASR in XGI offers advantages such as simplified phase retrieval algorithm, reduced overall radiation dose, and improved image acquisition speed. These advantages, as well as the limitations of the proposed method, are systematically investigated in this paper.

The external and internal structures of Amphizoa davidi Lucas (Coleoptera, Amphizoidae), using X-ray phase contrast microtomography.

The Chinese endemic water beetle Amphizoa davidi Lucas, is a rare and endangered species belonging to the monotypic family Amphizoidae (Coleoptera: Adephaga). A study of the external and internal structures of A. davidi is here presented, by using X-ray phase contrast tomography and light microscopy. Morphological details and three dimensional (3D) structures of this species are provided: skeletons, muscles, reproductive organs of male and female, nervous system, alimentary canal and pygidial gland. The reproductive organs of females are compared in two different developmental phases (ages): before copulation without mature ovaries and after copulation with mature ovaries. Such detailed 3D tomographic study based on micro-CT technology may promote our understanding of the detailed morphology in Amphizoidae and Coleoptera in general.

A novel crystal-analyzer phase retrieval algorithm and its noise property.

A description of the rocking curve in diffraction enhanced imaging (DEI) is presented in terms of the angular signal response function and a simple multi-information retrieval algorithm based on the cosine function fitting. A comprehensive analysis of noise properties of DEI is also given considering the noise transfer characteristic of the X-ray source. The validation has been performed with synchrotron radiation experimental data and Monte Carlo simulations based on the Geant4 toolkit combined with the refractive process of X-rays, which show good agreement with each other. Moreover, results indicate that the signal-to-noise ratios of the refraction and scattering images are about one order of magnitude better than that of the absorption image at the edges of low-Z samples. The noise penalty is drastically reduced with the increasing photon flux and visibility. Finally, this work demonstrates that the analytical method can build an interesting connection between DEI and GDPCI (grating-based differential phase contrast imaging) and is widely suitable for a variety of measurement noise in the angular signal response imaging prototype. The analysis significantly contributes to the understanding of noise characteristics of DEI images and may allow improvements to the signal-to-noise ratio in biomedical and material science imaging.

High sensitivity phase retrieval method in grating-based x-ray phase contrast imaging.

PURPOSE: Grating-based x-ray phase contrast imaging is considered as one of the most promising techniques for future medical imaging. Many different methods have been developed to retrieve phase signal, among which the phase stepping (PS) method is widely used. However, further practical implementations are hindered, due to its complex scanning mode and high radiation dose. In contrast, the reverse projection (RP) method is a novel fast and low dose extraction approach. In this contribution, the authors present a quantitative analysis of the noise properties of the refraction signals retrieved by the two methods and compare their sensitivities. METHODS: Using the error propagation formula, the authors analyze theoretically the signal-to-noise ratios (SNRs) of the refraction images retrieved by the two methods. Then, the sensitivities of the two extraction methods are compared under an identical exposure dose. Numerical experiments are performed to validate the theoretical results and provide some quantitative insight. RESULTS: The SNRs of the two methods are both dependent on the system parameters, but in different ways. Comparison between their sensitivities reveals that for the refraction signal, the RP method possesses a higher sensitivity, especially in the case of high visibility and/or at the edge of the object. CONCLUSIONS: Compared with the PS method, the RP method has a superior sensitivity and provides refraction images with a higher SNR. Therefore, one can obtain highly sensitive refraction images in grating-based phase contrast imaging. This is very important for future preclinical and clinical implementations.

Experimental exploration of mouse kidney imaging with the SR PCI technology.

This paper explores mouse kidney imaging with diffraction enhanced imaging (DEI) and inline outline X-ray imaging (IOXI) technology, and evaluates latent value of kidney imaging with phase contrast imaging technology. In our experiment, spatial resolution and tissue contrast serve as element evaluation and comparison. Images obtained from our experiment exhibit clearly observable contrasts and high resolution, suggesting X-RAY and IOXO are suitable for capturing kidney images. Also, further comparison shows IOXO has a better performance than DEI in capturing microstructures.

Scattering imaging method in transmission x-ray microscopy.

We present a x-ray microscopy technique based on structured illumination in a microscope that characterizes the size of the subresolution-limit features. The technique is effective for characterizing fine structures substantially beyond the Rayleigh resolution of the microscope. We carried out optical experiments to demonstrate the basic principle of this new technique. Experimental results show good agreement with theoretical predictions. This technique should find a wide range of important imaging applications with a feature size down to nanometer scale, such as oil and gas reservoir rocks, advanced composites, and functional nanodevices and materials.

A theoretically exact reconstruction algorithm for helical cone-beam differential phase-contrast computed tomography.

Differential phase-contrast computed tomography (DPC-CT) reconstruction problems are usually solved by using parallel-, fan- or cone-beam algorithms. For rod-shaped objects, the x-ray beams cannot recover all the slices of the sample at the same time. Thus, if a rod-shaped sample is required to be reconstructed by the above algorithms, one should alternately perform translation and rotation on this sample, which leads to lower efficiency. The helical cone-beam CT may significantly improve scanning efficiency for rod-shaped objects over other algorithms. In this paper, we propose a theoretically exact filter-backprojection algorithm for helical cone-beam DPC-CT, which can be applied to reconstruct the refractive index decrement distribution of the samples directly from two-dimensional differential phase-contrast images. Numerical simulations are conducted to verify the proposed algorithm. Our work provides a potential solution for inspecting the rod-shaped samples using DPC-CT, which may be applicable with the evolution of DPC-CT equipments.

A new method to retrieve phase information for equiangular fan beam differential phase contrast computed tomography.

PURPOSE: Sample radiation damage is one of the main drawbacks limiting applications of the x-ray phase-contrast imaging method. Recently, for x-ray grating-based phase contrast imaging, the reverse projection (RP) method has been proposed by Zhu et al. [Proc. Natl. Acad. Sci. U.S.A. 107, 13576-13581 (2010)]. Compared to the conventional phase stepping technique, the RP method allows a strong reduction of the exposure time and minimization of the errors induced by mechanical vibrations. However, so far, it has only been considered for parallel beam illumination, typical of a synchrotron radiation source. In this paper, a generalization of the RP method from parallel beam geometry to fan beam geometry was presented and discussed. METHODS: Within parallel beam geometry, the RP method utilizes the conjugate characteristic between reverse projection images. Nevertheless, this characteristic is not directly satisfied for fan beam geometry. In this study, a phantom composed of known materials was constructed and the projection images of the phantom were calculated in a fan beam geometry. By considering single ray, the conjugate images of the projection images were derived from the projection dataset. After that, using the modified RP method the authors retrieved phase and absorption information from paired images. RESULTS: Extracted phase and absorption information of the phantom were in good agreement with theoretical values. Additionally, the slice reconstruction was performed and the results turned out to be in the authors' expectation. CONCLUSIONS: Theoretical calculations and numerical simulations confirm both feasibility and validity of the RP method under fan beam illumination. Because this method is simple, fast, and releases a relatively low dose, the authors believe that this research is very useful for the x-ray phase contrast imaging applications in clinical diagnosis, bioresearch, and industrial nondestructive testing.

Advantages of intermediate X-ray energies in Zernike phase contrast X-ray microscopy.

Understanding the hierarchical organizations of molecules and organelles within the interior of large eukaryotic cells is a challenge of fundamental interest in cell biology. Light microscopy is a powerful tool for observations of the dynamics of live cells, its resolution attainable is limited and insufficient. While electron microscopy can produce images with astonishing resolution and clarity of ultra-thin (<1 µm thick) sections of biological specimens, many questions involve the three-dimensional organization of a cell or the interconnectivity of cells. X-ray microscopy offers superior imaging resolution compared to light microscopy, and unique capability of nondestructive three-dimensional imaging of hydrated unstained biological cells, complementary to existing light and electron microscopy. Until now, X-ray microscopes operating in the "water window" energy range between carbon and oxygen k-shell absorption edges have produced outstanding 3D images of cryo-preserved cells. The relatively low X-ray energy (<540 eV) of the water window imposes two important limitations: limited penetration (<10 µm) not suitable for imaging larger cells or tissues, and small depth of focus (DoF) for high resolution 3D imaging (e.g., ~1 µm DoF for 20 nm resolution). An X-ray microscope operating at intermediate energy around 2.5 keV using Zernike phase contrast can overcome the above limitations and reduces radiation dose to the specimen. Using a hydrated model cell with an average chemical composition reported in literature, we calculated the image contrast and the radiation dose for absorption and Zernike phase contrast, respectively. The results show that an X-ray microscope operating at ~2.5 keV using Zernike phase contrast offers substantial advantages in terms of specimen size, radiation dose and depth-of-focus.

Visualising liver fibrosis by phase-contrast X-ray imaging in common bile duct ligated mice.

OBJECTIVES: To determine whether phase-contrast X-ray imaging can be used to visualise directly the accumulated extracellular matrix proteins associated with liver fibrosis in common bile duct ligated mice. METHODS: Twenty-six-week-old C57BL female mice were randomised into three groups. In groups 1 (n = 5) and 2 (n = 10), common bile duct ligation was conducted to produce secondary biliary cirrhosis. Mouse livers were then excised 15 (group 1) and 40 days (group 2) after the ligation of the common bile duct for imaging. In the control group, the livers of 5 mice were excised 40 days after the sham operation. Images were then acquired using the analyser crystal set at different positions of the rocking curve. RESULTS: The results show that the fibrotic septa and hepatic lobules enclosed by fibrotic septa can be visualised clearly at the whole organ level via phase-contrast X-ray imaging without any contrast agent. CONCLUSION: These results suggest that phase-contrast X-ray imaging can easily reveal the accumulated extracellular matrix proteins associated with liver fibrosis without using any contrast agent and has great potential in the study of liver fibrosis.

A 30 nm-resolution hard X-ray microscope with X-ray fluorescence mapping capability at BSRF.

A full-field transmission X-ray microscope (TXM) operating continuously from 5 keV to 12 keV with fluorescence mapping capability has been designed and constructed at the Beijing Synchrotron Radiation Facility, a first-generation synchrotron radiation facility operating at 2.5 GeV. Spatial resolution better than 30 nm has been demonstrated using a Siemens star pattern in both absorption mode and Zernike phase-contrast mode. A scanning-probe mode fluorescence mapping capability integrated with the TXM has been shown to provide 50 p.p.m. sensitivity for trace elements with a spatial resolution (limited by probing beam spot size) of 20 µm. The optics design, testing of spatial resolution and fluorescence sensitivity are presented here, including performance measurement results.

Extended depth of focus for transmission x-ray microscope.

A fast discrete curvelet transform based focus-stacking algorithm for extending the depth of focus of a transmission x-ray microscope (TXM) is presented. By analyzing an image stack of a sample taken in a Z-scan, a fully in-focus image can be generated by the proposed scheme. With the extended depth of focus, it is possible to obtain 3D structural information over a large volume at nanometer resolution. The focus-stacking method has been demonstrated using a dataset taken with a laboratory x-ray source based TXM system. The possibility and limitations of generalizing this method to a synchrotron based TXM are also discussed. We expect the proposed method to be of important impact in 3D x-ray microscopy.

High-speed X-ray microscopy by use of high-resolution zone plates and synchrotron radiation.

X-ray microscopy based on synchrotron radiation has become a fundamental tool in biology and life sciences to visualize the morphology of a specimen. These studies have particular requirements in terms of radiation damage and the image exposure time, which directly determines the total acquisition speed. To monitor and improve these key parameters, we present a novel X-ray microscopy method using a high-resolution zone plate as the objective and the matching condenser. Numerical simulations based on the scalar wave field theory validate the feasibility of the method and also indicate the performance of X-ray microscopy is optimized most with sub-10-nm-resolution zone plates. The proposed method is compatible with conventional X-ray microscopy techniques, such as computed tomography, and will find wide applications in time-resolved and/or dose-sensitive studies such as living cell imaging.