Guohao Du

Fourier-transform Ghost Imaging with Hard X-rays

Knowledge gained through x-ray crystallography fostered structural determination of materials and greatly facilitated the development of modern science and technology in the past century. However, it is only applied to crystalline structures and cannot resolve noncrystalline materials. Here we demonstrate a novel lensless Fourier-transform ghost imaging method with pseudothermal hard x rays that extends x-ray crystallography to noncrystalline samples. By measuring the second-order intensity correlation function of the light, Fourier-transform diffraction pattern of a complex amplitude sample is achieved at the Fresnel region in our experiment and the amplitude and phase distributions of the sample in the spatial domain are retrieved successfully. For the first time, ghost imaging is experimentally realized with x rays. Since a highly coherent x-ray source is not required, the method can be implemented with laboratory x-ray sources and it also provides a potential solution for lensless diffraction imaging with fermions, such as neutrons and electrons where intensive coherent sources usually are not available.

Infrared analysis of the irradiation effects in aromatic polyimide films

A Fourier transform infrared (FTIR) spectroscopic investigation of the ion-beam-induced chemical and structural modification in polyimide (PI) films is presented. Our experimental considerations provide a foundation for a quantitative evaluation of the infrared (IR) results for this thermally stable polymer on the deterioration of chemical bonding with irradiation fluence. It is found that chemical structure in PI is subjected to a severe alteration within the dose range from 1 × 1014 to 1 × 1015 B+/cm2. The radical structure modification is completed only as irradiation reaches 1 × 1016 B+/cm2, at which point one may find that there exists a resemblance in profile shape between the IR spectrum of the high-dose irradiated PI film and the one-phonon states density (DOS) of amorphous graphite. This suggests that a structure similar to amorphous graphitic carbon films will be formed in the ion-beam-modified PI film when dose comes to a certain threshold. This “graphitization” process under ion bombardment is also supported by the experimental results from ultraviolet (UV)-visible spectroscopic study.

Fast and accurate X‐ray fluorescence computed tomography imaging with the ordered‐subsets expectation maximization algorithm

The ordered-subsets expectation maximization algorithm (OSEM) is introduced to X-ray fluorescence computed tomography (XFCT) and studied; here, simulations and experimental results are presented. The simulation results indicate that OSEM is more accurate than the filtered back-projection algorithm, and it can efficiently suppress the deterioration of image quality within a large range of angular sampling intervals. Experimental results of both an artificial phantom and cirrhotic liver show that with a satisfying image quality the angular sampling interval could be improved to save on the data-acquisition time when OSEM is employed. In addition, with an optimum number of subsets, the image reconstruction time of OSEM could be reduced to about half of the time required for one subset. Accordingly, it can be concluded that OSEM is a potential method for fast and accurate XFCT imaging.

Detection of microvasculature in rat hind limb using synchrotron radiation.

BACKGROUND New X-ray microangiography and third-generation synchrotron radiation-based micro-computed tomography have opened new perspectives for microvascular imaging of extremity. Here we aimed to visualize deep-level microvascular structure in rat hind limb by microangiographic technique, and compare images with those by conventional method. MATERIALS AND METHODS A total of 10 Sprague Dawley rats were used for in vivo and ex vivo study (five rats/group). Microangiography in vivo and ex vivo was performed and images were compared with those by conventional method. Synchrotron radiation-based micro-computed tomography (SRμCT) was also performed to reveal three-dimensional (3D) morphology of the blood vessel in rat hind limb. RESULTS By microangiographic technique, blood vessels in the rat limb could be clearly depicted with the minimum visualized blood vessel about 9 μm in diameter, and higher angiographic scores were achieved than those by conventional X-ray. In addition, the vascular network could be defined and analyzed at the micrometer scale from the 3D renderings of limb vessel as shown by SRμCT. CONCLUSIONS Synchrotron radiation-based microangiography and SRμCT thus provided a practical and effective means to observe the microvasculature of limbs, which might be useful in assessment of angiogenesis in lower limbs.

X-ray biomedical imaging beamline at SSRF

Since May 6, 2009, the X-ray biomedical imaging beamline at Shanghai Synchrotron Radiation Facility (SSRF) has been formally opened to users. The beamline is composed of a wiggler source with the intensity of magnetic field of 2.0 Tesla, a double crystal monochromator (DCM) cooled with liquid nitrogen, a 6-axis filter for high heat load reducing on the downstream optics such as Be window and DCM. The photon energy range for the monochromatic beam is 8-72.5keV. Three sets of digital X-ray detectors are provided to users with the pixel size range being 0.37-13 mu m. Several imaging methods such as micro-CT, in-line phase contrast imaging could be applied in biomedicine, material science and paleontology studies. The spatial resolution of 0.8 mu m and the temporal resolution of 1 ms could be realized. By the end of 2012, the beamline has provided more than 13900 hours beamtime for users, while over half of the research proposals come from biomedicine field. Nearly 2000 person-times have come and done their experiments at the beamline. More than 470 user proposals have been perfomed and more than 110 papers from users have been published. Some typical experimental results on biomedical applications will be introduced.

Anisotropic shrinkage of insect air sacs revealed in vivo by X-ray microtomography.

Air sacs are thought to be the bellows for insect respiration. However, their exact mechanism of action as a bellows remains unclear. A direct way to investigate this problem is in vivo observation of the changes in their three-dimensional structures. Therefore, four-dimensional X-ray phase contrast microtomography is employed to solve this puzzle. Quantitative analysis of three-dimensional image series reveals that the compression of the air sac during respiration in bell crickets exhibits obvious anisotropic characteristics both longitudinally and transversely. Volumetric changes of the tracheal trunks in the prothorax further strengthen the evidence of this finding. As a result, we conclude that the shrinkage and expansion of the insect air sac is anisotropic, contrary to the hypothesis of isotropy, thereby providing new knowledge for further research on the insect respiratory system.

Fast X-ray micro-tomography for low-Z materials

X-ray phase-contrast micro-tomography (XPCMT) is an important method for the non-destructive acquisition of internal information from samples composed of low-Z elements. During the development of XPCMT, its spatial resolution has gradually been improved; however, insufficient attention has been directed towards the improvement of its time resolution. The low time resolution of XPCMT restricts its applications in fast dynamic processes, such as the fermentation process and alloy growth. In this paper, we demonstrate a fast XPCMT method developed by combining the compressed sensing (CS) theory with XPCMT. This method allows for the accurate reconstruction of images using undersampled XPCMT data, thus achieving higher time resolution and simultaneously reducing the dose delivered to the samples; the latter is especially beneficial in medical applications. The CS-XPCMT algorithm was validated using experimental data from two samples, Fructus Foeniculi and a live ant, collected at the X-ray imaging and biomedical application beamline of the Shanghai Synchrotron Radiation Facility. The results for Fructus Foeniculi demonstrate that the CS-XPCMT algorithm yields good reconstruction accuracy for incomplete and undersampled data. Furthermore, the results for the live ant demonstrate that the CS-XPCMT algorithm is capable of performing fast XPCMT and is a potential method for the realisation of dynamic XPCMT, given appropriately upgraded experimental devices.

Phase contrast micro-computed tomography of biological sample at SSRF

Abstract In line X-ray phase contrast micro-computed tomography (IL-XPCT), which can be implemented at third generation synchrotron radiation sources or by using a micro-focus X-ray tube, is a powerful technique for non-destructive, high-resolution investigations of a broad variety of materials. At the Shanghai Synchrotron Radiation Facility (SSRF), the X-ray Imaging and Biomedical Applications Beamline was built and started regular user operation in May 2009. Both qualitative (without phase retrieval) and quantitative (with phase retrieval) three-dimensional IL-XPCT experimental techniques have been established at the beamline. IL-XPCT experiments of a test sample (plastic pipes) used to evaluate the technique, and of a biological sample (locust) at the beamline are reported. Two series of images, qualitative and quantitative, including tomographic slices and three-dimensional rendering images were obtained. In qualitative images, there is a strong edge-enhancement which leads to very clear sample contours, while in quantitative images, the edge-enhancement fades but quantitative measurement of samples phase information could be achieved. The experiments demonstrate that the combination of qualitative and quantitative images is useful for biological sample studies.

X-ray propagation-based equally sloped tomography for mouse brain

BACKGROUND The outstanding functional importance of the brain implies a strong need for brain imaging modalities. However, the current imaging approaches that target the brain in rodents remain suboptimal. OBJECTIVE AND METHODS In this paper, X-ray propagation-based phase contrast imaging combined with equally sloped tomography (PPCI-EST) was employed to nondestructively investigate the mouse brain. RESULTS The grey and white matters, which have extremely small differences in electron density, were clearly discriminated. The fine structures, including the corpus callosum (cc), the optic chiasma (ox) and the caudate putamen (CPu), were revealed. Compared to the filtered back projection reconstruction, the PPCI-EST significantly reduce projection number while maintaining sufficient image quality. CONCLUSIONS It could be a potential tool for fast and low-dose phase-contrast imaging to biomedical specimens.

Microangiography in Living Mice Using Synchrotron Radiation

Traditionally, there are no methods available to detect the fine morphologic changes of cerebrovasculature in small living animals such as rats and mice. Newly developed synchrotron radiation microangiography can achieve a fine resolution of several micrometers and had provided us with a powerful tool to study the cerebral vasculature in small animals. The purpose of this study is to identify the morphology of cerebrovasculature especially the structure of Lenticulostriate arteries (LSAs) in living mice using the synchrotron radiation source at Shanghai Synchrotron Radiation Facility (SSRF) in Shanghai, China. Adult CD‐1 mice weighing 35–40 grams were anesthetized. Nonionic iodine (Omnipaque, 350 mg I /mL) was used as a contrast agent. The study was performed at the BL13W1 beam line at SSRF. The beam line was derived from a storage ring of electrons with an accelerated energy of 3.5 GeV and an average beam current of 200 mA. X‐ray energy of 33.3 keV was used to produce the highest contrast image. Images w...