Four-dimensional x-ray phase tomography with Talbot interferometer and white synchrotron light

Conventional X-ray absorption contrast imaging does not depict soft tissues, such as cartilage, in sufficient detail. For visualization of the soft tissues, X-ray phase-contrast imaging is more sensitive than absorption-contrast imaging. The basic concept of the X-ray phase-contrast imaging used in this study is similar to that of differential interference contrast (Nomarski) microscopy. We applied Talbot-Lau X-ray interferometry to visualize the joint structures in the right hand and knee of a donated cadaver. This imaging system simultaneously produced three different types of images: an absorption image, a differential phase image, and a visibility image. The interface between the articular cartilage of the metacarpo-phalangeal joint and fluid or the bony cortex was clearly demonstrated on the differential phase image, whereas this interface was unclear on the absorption image. Within the knee joint, the surface of the articular cartilage was demonstrated both on the differential phase and visibility images; the medial collateral ligament and medial meniscus were also visualized successfully. These results are clinically significant for the diagnosis and therapeutic estimation of rheumatoid arthritis and related joint diseases. This feasibility study on the clinical application of this imaging tool was a collaborative effort of researchers in the fields of physics, radiology, and gross anatomy.

We are attempting to expand the technology of X-ray grating phase imaging/tomography to enable dynamic observation. X-ray phase imaging has been performed mainly for static cases, and this challenge is significant since properties of materials (and hopefully their functions) would be understood by observing their dynamics in addition to their structure, which is an inherent advantage of X-ray imaging. Our recent activities in combination with white synchrotron radiation for this purpose are described. Taking advantage of the fact that an X-ray grating interferometer functions with X-rays of a broad energy bandwidth (and therefore high flux), movies of differential phase images and visibility images are obtained with a time resolution of a millisecond. The time resolution of X-ray phase tomography can therefore be a second. This study is performed as a part of a project to explore X-ray grating interferometry, and our other current activities are also briefly outlined.

Focusing polycapillary optics yield high gains in intensity and increased spatial resolution for a variety of clinical, lab-based, synchrotron, or in situ analysis applications. In this dissertation we investigate the extension of two applications of focusing polycapillary optics. The first is the application of polycapillary optics in radiation therapy. This discussion includes measurements and calculation of dose for focused beam orthovoltage therapy. A system has been designed to investigate whether the polycapillary optics can produce an X-ray beam which can give more accurate dose painting due to the higher dose concentration at the focal spot. X-ray exposures were measured with radio sensitive film. The measured spectrum of the X-ray beam was used to calculate the dose and compared with the measured dose on the films. The second application is medical imaging and quantitative phase retrieval. X-ray phase imaging can display subtle differences in low-density materials more readily than conventional X-ray imaging. However, due to spatial coherence requirements on the X-ray source, producing X-ray phase images has traditionally required either highly specialized sources, such as synchrotrons or small and low power microfocus sources, or multiple exposures with several carefully stepped precision gratings. To find appropriate approaches for enabling X-ray phase imaging in a clinically meaningful way, two techniques were tested. First, focusing polycapillary optics were applied in this work with conventional X-ray sources to enable propagation-based X-ray phase imaging. Quantitative phase retrieval was compared for two simple computational algorithms. Second, mesh-based X-ray phase imaging was demonstrated. In this technique, a simple, low-cost, coarse wire mesh and simple processing relaxes the spatial coherence constraint and allows quantitative phase retrieval. The mesh-based system combined with polycapillary optics significantly improved the accuracy of quantitative phase retrieval.

The recent use of a one-dimensional (1D) X-ray Talbot interferometer has triggered great interest in X-ray differential phase contrast imaging. As an improved version of a 1D interferometer, the development of two-dimensional (2D) grating interferometry strongly stimulated applications of grating-based imaging. In the framework of Fresnel diffraction theory, we investigated the self-image of 2D-phase gratings under partially coherent illumination. The fringe visibility of the self-image has been analyzed as a function of the spatial coherence length. From the viewpoint of self-image visibility, it is possible to find the optimal 2D grid for 2D X-ray grating interferometer imaging. Numerical simulations have been also carried out for quantitative evaluation. Results, in good agreement with theoretical analysis, indicate the spatial coherence requirements of the radiation illuminating a 2D grating interferometer. Moreover, our results can be used to optimize performances of a 2D grating interferometer and for further theoretical and experimental research on grating-based imaging systems.

The initial result of using a single 2-D checkerboard phase-grating Talbot interferometer as a feed-back loop sensor element of an adaptive x-ray mirror system is reported. The test was performed by measuring the surface profile of a deformable Pt coated Silicon mirror at five different actuation states. The reflected beam was detected at the fractional Talbot distance of a π/2 phase grating. The measured interferograms were de-convolved using the spatial harmonic imaging technique to extract the phase and amplitude of the reflected wavefront. The wavefront was then propagated to the mirror center to retrieve the surface profile of the mirror. The activation of a single actuator was easily detected from the reconstructed surface profile of the mirror. The presented results indicate that the single phase-grating x-ray Talbot interferometer is capable of sensing nano-meter scale profile changes of an adaptive mirror.

A high resolution micro computed tomography (micro-CT) system for live small animal imaging has been developed. The system consists of an x-ray source with micro focus spot and high brightness, rotating gantry with a x-ray tube and flat panel detector pair and a stationary and a horizontally positioned small animal bed to achieve a conebeam mode scan. The system is optimized for in vivo small animal imaging and the capability of administering respiratory anesthesia during scanning. The Feldkamp algorithm was adopted in image reconstruction with graphic processing unit (GPU). We evaluated the spatial resolution, image contrast, and uniformity of system using phantom. As the result, the spatial resolution of the system was the 56lp/mm at 10% of the MTF curve, and the radiation dose to the sample was 98mGy. The minimal resolving contrast was found to be less than 46 CT numbers on low-contrast phantom. We present the image test results of the bone and lung, and heart of the live mice.

Grating-based x-ray phase-contrast imaging is a fast developing new modality not only for medical imaging, but as well for other fields such as material sciences. While these many possible applications arise, the knowledge of the noise behavior is essential. In this work, the authors used a least squares fitting algorithm to calculate the noise behavior of the three quantities absorption, differential phase, and dark-field image. Further, the calculated error formula of the differential phase image was verified by measurements. Therefore, a Talbot interferometer was setup, using a microfocus x-ray tube as source and a Timepix detector for photon counting. Additionally, simulations regarding this topic were performed. It turned out that the variance of the reconstructed phase is only dependent of the total number of photons used to generate the phase image and the visibility of the experimental setup. These results could be evaluated in measurements as well as in simulations. Furthermore, the correlation between absorption and dark-field image was calculated. These results provide the understanding of the noise characteristics of grating-based phase-contrast imaging and will help to improve image quality.

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.

X-ray phase imaging based on the Lau effect is demonstrated with an incoherent laboratory X-ray source. Its optical configuration resembles the inverse geometry of the X-ray Talbot–Lau interferometer, which employs a large-area amplitude grating. However, the proposed approach avoids the use and hence fabrication difficulty of such a grating, which is advantageous when constructing an X-ray phase imaging apparatus. With a Mo-target source, differential phase images of polymer spheres were successfully obtained and a design concept for downsizing the system is also described.

An X-ray Talbot interferometer consisting of two capillary plates, which were used as X-ray amplitude gratings, was evaluated for X-ray phase imaging. A theoretical aspect of capillary X-ray Talbot interferometry is presented with a preliminary operation result using synchrotron radiation. A two-dimensional X-ray Talbot effect, or self-imaging effect, which was the basis of Talbot interferometry, was observed with the capillary plate, and moiré images formed by the X-ray Talbot interferometer exhibited contrasts corresponding to the differential phase shift caused by phase objects placed in front of the interferometer. Finally, the possibility of quantitative phase measurement with a fringe scanning technique is discussed.

When imaging soft tissues with hard X-rays, phase contrast is often preferred over conventional attenuation contrast due its superior sensitivity. However, it is unclear which of the numerous phase tomography methods yields the optimized results at given experimental conditions. Therefore, we quantitatively compared the three phase tomography methods implemented at the beamline ID19 of the European Synchrotron Radiation Facility: X-ray grating interferometry (XGI), and propagation-based phase tomography, i.e., single-distance phase retrieval (SDPR) and holotomography (HT), using cancerous tissue from a mouse model and an entire heart of a rat. We show that for both specimens, the spatial resolution derived from the characteristic morphological features is about a factor of two better for HT and SDPR compared to XGI, whereas the XGI data generally exhibit much better contrast-to-noise ratios for the anatomical features. Moreover, XGI excels in fidelity of the density measurements, and is also more robust against low-frequency artifacts than HT, but it might suffer from phase-wrapping artifacts. Thus, we can regard the three phase tomography methods discussed as complementary. The application will decide which spatial and density resolutions are desired, for the imaging task and dose requirements, and, in addition, the applicant must choose between the complexity of the experimental setup and the one of data processing.

Phase tomography based on hard X-ray double-grating interferometry (XDGI) is a well-established imaging technique for the three-dimensional visualization of soft tissues, providing tomograms with superior contrast. The experimental setup contains a beam-splitter grating and an analyzer grating. Both gratings have to be placed and oriented with high precision for an optimized functioning of the interferometer. The analyzer grating can be omitted, if the detection unit allows a direct detection of the interference pattern. Such a setup is termed hard X-ray single-grating interferometer (XSGI). XSGI profits from easier handling, as only one grating needs to be aligned, and from the related cost reduction. But, more importantly than that, for the XSGI the spatial resolution is not limited by the period of the analyzer grating, and for equal photon flux, the number of detected photons is increased by a factor of about two. In the present thesis, a peripheral human nerve was embedded in paraffin. In order to compare the performance of XSGI and XDGI for medically relevant, low-absorbing specimens, for both modalities the specimen was measured at the facility Deutsches Elektronen-Synchrotron (DESY), using synchrotron radiation. Subsequently, the acquired tomograms were superimposed using rigid registration, i.e. one dataset was translated and rotated to best fit the other one. Both techniques allow resolving anatomical features of the nerve investigated, including epineurium, perineurium, and endoneurium. Whereas the XDGI data exhibit a better contrast-to-noise ratio, the XSGI tomogram shows an improved spatial resolution by a factor close to two. Thus, it can be concluded that XSGI is the preferred approach for the visualization of paraffin-embedded soft tissues.

Developments in positron emission tomography (PET) technology have resulted in systems with finer detector elements designed to further improve spatial resolution. However, there is a limit to what extent reducing detector element size will improve spatial resolution in PET. The spatial resolution of PET imaging is limited by several other factors, such as annihilation photon non-collinearity, positron range, off-axis detector penetration, detector Compton scatter, undersampling of the signal in the linear or angular directions for the image reconstruction process, and patient motion. The overall spatial resolution of the systems is a convolution of these components. Of these other factors that contribute to resolution broadening, perhaps the most uncertain, poorly understood, and, for certain isotopes, the most dominant effect is from positron range. To study this latter effect we have developed a Monte Carlo simulation code that models positron trajectories and calculates the distribution of the end point coordinates in water for the most common PET isotopes used: F, N, C and O. In this work we present some results from these positron trajectory studies and calculate what effect positron range has on the overall PET system spatial resolution, and how this influences the choice of PET system design parameters such as detector element size and system diameter. We found that the fundamental PET system spatial resolution limit set from detector size, photon non-collinearity and positron range alone varied from nearly 1 mm FWHM (2 mm FWTM) for a 10-20 cm diameter system typical for animal studies with F to roughly 4 mm FWHM (7 mm FWTM) for an 80 cm diameter system typical for human imaging using O.

Diastrophic dysplasia (DTD) is an incurable recessive chondrodysplasia caused by mutations in the SLC26A2 transporter responsible for sulfate uptake by chondrocytes. The mutations cause undersulfation of glycosaminoglycans in cartilage. Studies of dtd mice with a knock-in Slc26a2 mutation showed an unusual progression of the disorder: net undersulfation is mild and normalizing with age, but the articular cartilage degrades with age and bones develop abnormally. To understand underlying mechanisms, we studied newborn dtd mice. We developed, verified and used high-definition infrared hyperspectral imaging of cartilage sections at physiological conditions, to quantify collagen and its orientation, noncollagenous proteins, and chondroitin chains, and their sulfation with 6-μm spatial resolution and without labeling. We found that chondroitin sulfation across the proximal femur cartilage varied dramatically in dtd, but not in the wild type. Corresponding undersulfation of dtd was mild in most regions, but strong in narrow articular and growth plate regions crucial for bone development. This undersulfation correlated with the chondroitin synthesis rate measured via radioactive sulfate incorporation, explaining the sulfation normalization with age. Collagen orientation was reduced, and the reduction correlated with chondroitin undersulfation. Such disorientation involved the layer of collagen covering the articular surface and protecting cartilage from degradation. Malformation of this layer may contribute to the degradation progression with age and to collagen and proteoglycan depletion from the articular region, which we observed in mice already at birth. The results provide clues to in vivo sulfation, DTD treatment, and cartilage growth.

This paper firstly introduces the principle of distributed sensing system based on Polarization sensitive Optical Time-Domain Reflectometer (P-OTDR). As known, the change of State of Polarization (SOP) in fiber is sensitive to environment, consequently this sensing method can extract very little perturbation of extra temperature or strain; another significant advantage is that the sensing information can be achieved nondestructively at one end. Hence, this technique has become a practical and helpful tool in distributed optical fiber sensing system. However backscattered light in single-mode fiber is very weak, and the optical pulse width limits the spatial resolution, so there is a compromise between SNR and sensor spatial resolution. We investigate two signal-process methods to extract the state polarization (SOP) evolution from backscatted signal. From the experiment results, we find that both the digital average and deconvolution can be used for enhancing SNR and system spatial resolution. And we also find hundred of digital average is enough, the more time we average the less improvement of SNR we get. At the same time, we view that the SOP of backscattered signal is the response of sensing system. By mean of deconvolution the actual SOP evolution is not lost, and the spatial resolution of POTDR System doesn’t degrade with a wider pulse. Compared with previous deconvolution case, the deconvolution method can effectively improve the system spatial resolution without decreasing the transmitting pulse width. Finally we give some experiment results with strain perturbation, our system can detect the point where the environment changes, which is suitable for smart structure and optic-fiber sensor application.