This PDF file contains the front matter associated with SPIE Proceedings Volume 8506, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Trends in the type and distribution of published micro- and nano-CT studies are reviewed in this paper. The literature of the last two years is covered, i.e., the period between Developments in X-ray Tomography VII (2010) and the present. Use of microCT scanning in the natural history field is also described using the distribution of applications at one natural history museum equipped with a scanner.

Four-dimensional X-ray phase tomography has been implemented by a combination of X-ray Talbot interferometry and white synchrotron radiation. While the Fourier-transform method has been used for the measurement of a differential phase image at every projection direction, an improved scan mode based on the fringe-scanning method is demonstrated to improve spatial resolution. The disadvantage of the fringe-scanning method, which requires multiple moiré images, is overcome by proposing a scan mode synchronously combining one-way continuous movements of sample rotation and grating displacement. In addition, the operation of an X-ray Talbot-Lau interferometer with white synchrotron radiation is reported. While an X-ray Talbot interferometer requires a horizontal sample rotation axis because of the condition of spatial coherency, such a horizontal rotation axis is not preferable for tomographic scans especially for soft objects. An X-ray Talbot-Lau interferometer overcomes this problem, allowing a vertical sample rotation axis. Although we encountered a vibration problem with the X-ray Talbot-Lau interferometer probably because of incomplete stage stability, our attempts have basically been successful, and we expect that various samples can be scanned by four-dimensional X-ray phase tomography, revealing dynamical properties in weakly absorbing objects that cannot be accessed by conventional X-ray phase tomography mainly performed for static samples.

The brain has an outstanding functional importance in the human organism. Therefore, there is a strong need for three-dimensional brain imaging modalities. Magnetic resonance imaging provides deep insights but its spatial resolution is insufficient to study the structure on the cellular level. X-ray absorption microtomography yields the necessary spatial resolution, but shows only marginal contrast between the different types of brain tissue. Alternatively, differential X-ray phase contrast obtained with grating interferometry, which is known for much better differentiations between soft tissues can be used for the visualization of the human brain. As important structures of the human brain such as the human thalamus have dimensions of several centimeters, a large field of view is required. In the present communication, we report an evaluation of grating-based X-ray phase contrast microtomography in the off-axis modus which allows to expand the field of view up to a factor of two but may reduce the image quality. We demonstrate that tomograms with comparable contrast-to-noise values, about 10%, and 50% inferior spatial resolution can be generated with off-axis measurements. As one can reduce the effective pixel size up to a factor of two, the choice of an asymmetrical rotation axis can give rise to an improvement of the spatial resolution by 20%.

Basic research is required to develop more powerful approaches to prevent, diagnose, and above all to treat cancer, although the clever combination of surgery, chemical, pharmacological, and radiation therapies is well established. Our research activity concentrates on the quantification of the three-dimensional micro-morphology of vessel trees formed in cancerous and healthy tissues of a mouse model post mortem. While in several cases it is possible to extract the vessel tree from corrosion casts, phase contrast imaging modalities are needed for cancerous tissues with a significant amount of damaged vessel walls. Differences between cancerous and healthy tissues could be identified. The sum-of-angle metrics is found to be constant for vessel segments in cancerous and healthy tissues with lengths between 12 and 220 μm and corresponds to (0.62 ± 0.10) rad/μm.

Atherosclerosis, the narrowing of vessel diameter and build-up of plaques in coronary arteries, leads to an increase in the shear stresses present, which can be used as a physics-based trigger for targeted drug delivery. In order to develop appropriate nanometer-size containers, one has to know the morphology of the critical stenoses with isotropic micrometer resolution. Micro computed tomography in absorption and phase contrast mode provides the necessary spatial resolution and contrast. The present communication describes the pros and cons of the conventional and synchrotron radiation-based approaches in the visualization of diseased human and murine arteries. Using registered datasets, it also demonstrates that multi-modal imaging, including established histology, is even more powerful. The tomography data were evaluated with respect to cross-section, vessel radius and maximal constriction. The average cross-section of the diseased human artery (2.31 mm²) was almost an order of magnitude larger than the murine one (0.27 mm²), whereas the minimal radius differs only by a factor of two (0.51 mm versus 0.24 mm). The maximal constriction, however, was much larger for the human specimen (85% versus 49%). We could also show that a plastic model used for recent experiments in targeted drug delivery represents a very similar morphology, which is, for example, characterized by a maximal constriction of 82%. The tomography data build a sound basis for flow simulations, which allows for conclusions on shear stress distributions in stenosed blood vessels.

Stored in various public archives and private collections around the world, there are untold numbers of documents whose content is lost to memory and history. They cannot be read by normal means, because the parchment and paper they are written on has degraded; any attempt to handle or process the document for reading will at the very least cause it permanent damage. One of the prime catalysts of document degradation is the iron gall ink used in their writing; this provides a contrast for X-Ray imaging. The low attenuation produced by the tiny quantities of iron and other metals in the inks requires a system with a very high contrast ratio and excellent immunity from artifacts to enable ink imaging. The new generation XMT TDI scanner being developed at Queen Mary fulfills these criteria. A 3D volumetric dataset produced by XMT scanning the document is modeled and digitally re-created, producing a readable image of the text. The post-processing is performed in six stages, noise removal, data segmentation, surface construction, flattening, data projection and image generation. The scanning process takes upwards of a day, so it is important that the documents are not damaged by long exposure to the X-Ray flux. Investigations ongoing and due to be be published have shown no detectable extra damage to either old or modern scanned parchment.

By amalgamating a transmission X-Ray diffraction (XRD) experiment with grain boundary tracking (GBT) that has been developed by the present authors by combining the X-ray micro-tomography (CT) and the gallium-enhanced grain boundary visualization techniques, a novel method which provides accurate crystallographic information of individual grains during deformation has been created. The developed technique, which is called diffraction-amalgamated grain boundary tracking (DAGT) technique, is non-destructive for in-situ characterizing of bulk materials, which allows for close to deformation and fracture analysis of metals. Employing near field XRD analysis with a thin collimated X-ray beam, the algorithms developed for DAGT identifies which diffraction spots are related to which grain; consequently, providing a description of the misorientation between grains. DAGT also realizes micron-level analysis of grain morphologies and local stain distribution in 3-dimensions (3D) on the basis of CT observation, enabling the crystallographic interpretation of localized deformation without being affected by blurring of diffraction spots caused by deformation. An Al-3mass%Cu alloy was used for demonstration purpose.

The numerical simulation of the response of bone tissue to loading is a very common method in the biomedical engineering. The high diversity of bone quality, fractures and metabolic diseases, requires different approaches to numerical simulation. The main aim of this study was image-based finite element modeling (FEM) of the three-point bending tests of cortical bone. The results from the simulation performed based on own materials can be then used to non-destructive prediction of the bone mechanical strength. The samples were scanned by X-ray microcomputed tomography (XMT). Grey values of the imaged phantom were calibrated to known values of the phantom densities. It enabled estimation of the calibration curve for mineral level in bone, that was further applied to the calculation of bone density and the estimation of the material parameters in the FE model. In one example, the finite element analysis gives the deflection y=0.7 mm that match results from experiments where deflection was equal to y =0,69mm. The reported studies delivered useful data for future prediction of the mechanical parameters based on only imaging data.

The goal of the MuCAT scanner development at Queen Mary University of London is to provide highly accurate maps of a specimen’s X-ray linear attenuation coefficient; speed of data acquisition and spatial resolution having a lower priority. The reason for this approach is that the primary application is to accurately map the mineral concentration in teeth. Synchrotron tomography would generally be considered more appropriate for such a task, but many of the dental applications involve repeated scans with long intervening periods (from hours to weeks) and the management of synchrotron facilities does not readily allow such research. Development work is concentrated in two areas: beam hardening correction algorithms and novel scanning methodology. Beam hardening correction is combined with calibration, such that the raw X-ray projection data is corrected for beam hardening prior to reconstruction. Recent developments include the design of a multi-element calibration carousel. This has nine calibration pieces, five aluminium, three titanium and one copper. Development of the modelling algorithm is also yielding improved accuracy. A time-delay integration CCD camera is used to avoid ring artefacts. The original prototype averaged out inhomogeneities in both the detector array and the X-ray field; later designs used only software correction for the latter. However, at lower X-ray energies, the effect of deposits on the X-ray window (for example) becomes more conspicuous and so a new scanning methodology has been designed whereby the specimen moves in an arc about the source and equiangular data is acquired, thus overcoming this problem.

Wood is a versatile tissue complex composed of different cell types such as tracheids, fibers, vessels and parenchyma cells, that each fulfills specific tasks within the woody body of a tree. However, even within a tree genus wood structure can differ significantly due to either biotic or abiotic stress factors occurring during the growth season, or due to cultivar specific growth characteristics. Typical tools for structural analysis of wood so far are scanning electron microscopy (SEM) and light microscopy, allowing measurements of sectional planes. However, the detection of boundary surfaces between neighboring cells and interconnectivity can only be observed in a restricted dimension. In our investigations at DESY, Hamburg, we applied SRμCT for characterization of small wood samples of poplar (Populus trichocarpa) to gain a three dimensional image of a small scale sample that allows us to visualize size, volume, form and interconnectivity of the cells in a non-destructive way. Dependent on sample size, high resolution of micro-structure can be gained. This technique is appropriate to calculate volumes, e.g. of water transported in vessel cells. Since it is possible to reconstruct the vessel network within a stem section, effects of wounding or other environmental stresses on the xylem structure in general, and particularly on the water transport system, might be detected and visualized in 3D by synchrotron radiation-based microtomography. Hence this method is a most promising tool for future investigations in the field of plant physiology.

All lung disease dramatically alters the local motion of the lung during breathing. It stands to reason, therefore, that detailed measurement of lung motion could provide dramatic improvements in assessment of lung function. Using synchrotron-based phase contrast imaging, we have developed and applied tools for lung motion and function measurement. We demonstrate a low-dose alternative to traditional 4D-CT methods, capable of measuring instantaneous 3D tissue motion using only 6 projection images. Additionally, our technique provides estimation of the airflow distribution throughout the bronchial tree during the breathing cycle. The ability to measure lung function at a regional level will provide invaluable information for studies into normal and pathological lung dynamics, and may provide new pathways for diagnosis of regional lung diseases. Although proof-of-concept data were acquired on a synchrotron, the low-dose methodology developed lends itself to clinical scanning and offers translational opportunities.

In many animals, including humans, the lungs encase the majority of the heart thus the motion of each organ affects the other. The effects of the motion of the heart on the lungs potentially provides information with regards to both lung and heart health. We present a novel technique that is capable of measuring the effect of the heart on the surrounding lung tissue through the use of advanced synchrotron imaging techniques and recently developed X-ray velocimetry methods. This technique generates 2D frequency response maps of the lung tissue motion at multiple projection angles from projection X-ray images. These frequency response maps are subsequently used to generate 3D reconstructions of the lung tissue exhibiting motion at the frequency of ventilation and the lung tissue exhibiting motion at the frequency of the heart. This technique has a combined spatial and temporal resolution sufficient to observe the dynamic and complex 3D nature of lung-heart interactions.

A fast micro-tomography system and a high throughput micro-tomography system using state-of-the-art Complementary Metal Oxide Semiconductor (CMOS) imaging devices have been developed at SPring-8. Those systems adopt simple projection type tomography using synchrotron radiation X-ray. The fast micro-tomography system achieves a scan time around 2 s with 1000 projections, which is 15 times faster than previously developed system at SPring-8. The CMOS camera for fast tomography has 64 Giga Byte on-board memory, therefore, the obtained images must be transferred to a PC at the appropriate timing. A melting process of snow at room temperature was imaged every 30 s as a demonstration of the system. The high throughput tomography system adopts a scientific CMOS (sCMOS) camera with a low noise and high quantum efficiency. The system achieves a scan time around 5 minutes which is three times faster than before. The images quality of the system has been compared to the existing system with Charge-Coupled Device (CCD) camera. The results have shown the advantage of the new sCMOS camera.

We have developed a compact grating-based in-vivo phase-contrast micro-CT system with a rotating gantry. The 50 W microfocus x-ray source operates with 20 to 50 kV peak energy. The length of the rotating interferometer is around 47 cm. Pixel size in the object is 30 micron; the field of view is approx. 35 mm in diameter, suited to image a mouse. The interferometer consists of three gratings: an absorption grating close to the x-ray source, a phase grating to introduce a π/2 phase shift and an absorption analyzer grating positioned at the first fractional Talbot distance. Numerous drives and actuators are used to provide angular and linear grating alignment, phase stepping and object/gantry precision positioning. Phantom studies were conducted to investigate performance, accuracy and stability of the scanner. In particular, the influences of gantry rotation and of temperature fluctuations on the interferometric image acquisition were characterized. Also dose measurements were performed. The first imaging results obtained with the system show the complementary nature of phase-contrast micro-CT images with respect to absorption-based micro-CT. Future improvements, necessary to optimize the scanner for in-vivo small-animal CT scanning on a regular and easy-to-use basis, are also discussed.

State-of-art synchrotron radiation based micro-computed tomography provides high spatial and temporal resolution. This matches the needs of many research problems in geosciences. In this letter we report the current capabilities in microtomography at sector 2BM at the Advanced Photon Source (APS) of Argonne National Laboratory. The beamline is well suited to routinely acquire three-dimensional data of excellent quality with sub-micron resolution. Fast cameras in combination with a polychromatic beam allow time-lapse experiments with temporal resolutions of down to 200 ms. Data processing utilizes quantitative phase retrieval to optimize contrast in phase contrast tomographic data. The combination of these capabilities with purpose-designed experimental cells allows for a wide range of dynamic studies on geoscientific topics, two of which are summarized here. In the near future, new experimental cells capable of simulating conditions in most geological reservoirs will be available for general use. Ultimately, these advances will be matched by a new wide-field imaging beam line, which will be constructed as part of the APS upgrade. It is expected that even faster tomography with larger field of view can be conducted at this beam line, creating new opportunities for geoscientific studies.

During the last decade, X-ray micro Computerized Tomography (CT) has become a conventional technique for the three-dimensional (3D) investigation of trabecular bone micro-architecture. Coupling micro-CT to synchrotron sources possesses significant advantages in terms of image quality and gives access to information on bone mineralization which is an important factor of bone quality. We present an overview of the investigation of bone using Synchrotron Radiation (SR) CT from the micro to the nano scale. We introduce two synchrotron CT systems developed at the ESRF based on SR parallel-beam micro-CT and magnified phase CT respectively, achieving down to submicrometric and nanometric spatial resolution. In the latter, by using phase retrieval prior to tomographic reconstruction, the system provides maps of the 3D refractive index distribution. Parallel-beam SR micro-CT has extensively been used for the analysis of trabecular or cortical bone in human or small animals with spatial resolution in the range [3-10] μm. However, the characterization of the bone properties at the cellular scale is also of major interest. At the micrometric scale, the shape, density and morphology of osteocyte lacunae can be studied on statistically representative volumes. At the nanometric scale, unprecedented 3D displays of the canaliculi network have been obtained on fields of views including a large number of interconnected osteocyte lacunae. Finally SR magnified phase CT provides a detailed analysis of the lacuno-canalicular network and in addition information on the organization of the collagen fibers. These findings open new perspectives for three-dimensional quantitative assessment of bone tissue at the cellular scale.

Bone augmentation is a vital part of surgical interventions of the oral and maxillofacial area including dental implantology. Prior to implant placement, sufficient bone volume is needed to reduce the risk of peri-implantitis. While augmentation using harvested autologous bone is still considered as gold standard, many surgeons prefer bone substitutes to reduce operation time and to avoid donor site morbidity. To assess the osteogenic efficacy of commercially available augmentation materials we analyzed drill cores extracted before implant insertion. In younger patients, distraction osteogenesis is successfully applied to correct craniofacial deformities through targeted bone formation. To study the influence of mesenchymal stem cells on bone regeneration during distraction osteogenesis, human mesenchymal stem cells were injected into the distraction gap of nude rat mandibles immediately after osteotomy. The distraction was performed over eleven days to reach a distraction gap of 6 mm. Both the rat mandibles and the drill cores were scanned using synchrotron radiation-based micro computed tomography. The three-dimensional data were manually registered and compared with corresponding two-dimensional histological sections to assess bone regeneration and its morphology. The analysis of the rat mandibles indicates that bone formation is enhanced by mesenchymal stem cells injected before distraction. The bone substitutes yielded a wide range of bone volume and degree of resorption. The volume fraction of the newly formed bone was determined to 34.4% in the computed tomography dataset for the augmentation material Geistlich Bio-Oss^®. The combination of computed tomography and histology allowed a complementary assessment for both bone augmentation and distraction osteogenesis.

The complex hierarchical structure of human tooth hard tissues, enamel and dentin, guarantees function for decades. On the micrometer level the dentin morphology is dominated by the tubules, micrometer-narrow channels extending from the dentin-enamel junction to the pulp chamber. Their structure has been extensively studied, mainly with two-dimensional approaches. Dentin tubules are formed during tooth growth and their orientation is linked to the morphology of the nanometer-sized components, which is of interest for example for the development of bio-inspired dental fillings. Therefore, a method has to be identified that can access the three-dimensional organization of the tubules, e.g. density and orientation. Tomographic setups with pixel sizes in the sub-micrometer range allow for the three-dimensional visualization of tooth dentin tubules both in phase and absorption contrast modes. We compare high-resolution tomographic scans reconstructed with propagation based phase retrieval algorithms as well as reconstructions without phase retrieval concerning spatial and density resolution as well as rendering of the dentin microstructure to determine the approach best suited for dentin tubule imaging. Reasonable results were obtained with a single-distance phase retrieval algorithm and a propagation distance of about 75% of the critical distance of d²/λ, where d is the size of the smallest objects identifiable in the specimen and λ is the X-ray wavelength.

X-ray micro computed tomography (µCT) is a method of choice for the non-destructive imaging of static 3d samples. A fundamental constraint of conventional X-ray µCT is that the sample must remain static during data acquisition. It therefore can not be directly applied to the study of dynamic (i.e. 4D) processes such as pore-scale fluid displacements in porous materials. The process must be halted whilst data acquisition occurs, devaluing the experiment (e.g. the fluid displacement rate can no longer be studied with any confidence). Recent “proof-of-concept" studies have shown that “dynamic tomography" reconstruction algorithms incorporating a priori knowledge of the underlying physics of the process, may be capable of true high-resolution, time-resolved 4D imaging of continuous, complex processes at existing X-ray µCT facilities. In this paper, we seek to establish: (i) that the a priori information used in dynamic tomography is appropriate, i.e. does not bias the algorithm towards incorrect results; and (ii) that the results of the dynamic tomography algorithm agree with those produced by conventional techniques in the limiting case of a slowly changing sample. This investigation is performed using experimental data collected at the ANU µCT facility.

In synchrotron set-ups with a parallel x-ray beam, the spatial resolution is fully defined by the x-ray camera performance. This is also true in some laboratory x-ray imaging and CT instruments with an object position close to the detector. Fiber optic coupling does not allow camera resolutions reaching micron and submicron range, while cameras with lens coupling demonstrate resolutions close to diffraction limit, i.e. around 0.5 microns. Considering the conversion of x-rays to light in scintillator materials as a type of fluorescence under certain excitation, it should be possible to implement a method similar to Stochastic Optical Reconstruction Microscopy (STORM) in fluorescent microscopy to overcome diffraction limit in detector resolution. Our idea to overcome diffraction limit in such detectors is as follows. Every x-ray photon produces a significant amount of optical photons emitted from one particular point inside the scintillator. A fraction of the emitted optical photons is collected by a lens and hits the detector with a spread defined by the diffraction limit. Comparing the signal spread from every individual x-ray photon with the expected pre-calculated spread function, one can find the exact positions of primary x-ray photon. Using such exact positions to create images instead of collecting all incoming optical photons allows tracking exact positions of all original emitting points of x-ray photons without influence of optical diffraction limit. It can create images with a spatial resolution significantly better than what can be achieved in conventional diffraction limited optical acquisition.

Computers have changed remarkably in just the last 2-3 years. Memory is now very inexpensive, as little as $10/GB, or less than $1000 for 96GB. Computers with 8 or 12 cores are now inexpensive, starting at less than $3,000. This means that affordable workstations are in principle now capable of processing large tomography datasets. But for the most part tomography reconstruction software has not changed to take advantage of these new capabilities. Most installations use clusters of Linux machines, spreading the work over computers running multiple processes. It is significantly simpler and cheaper to run a single process that spreads the job over multiple threads running on multiple cores. tomoRecon is a new multi-threaded library for such tomography data reconstruction. It consists of only 545 lines of C++ code, on top of the ~800 lines in the Gridrec reconstruction code. The performance on a single modern workstation significantly exceeds dedicated clusters currently in use at synchrotron beamlines.

Synchrotron X-ray tomography offers many advantages for the study of flame retardants in polymer blends. The time to acquire the raw projection data is relatively short, the time required to reconstruct and view a 3D image is acceptable, and multiple data sets can be combined to yield 3D chemical distributions, a rather remarkable achievement. However, the workflow is not yet optimized, with too many steps requiring the interaction of a skilled scientist, the re-writing of complex computer codes, and the continued quest for new and improved data analyses. From the point-of-view of the industrial scientists, the attitudes range from “I need to learn more about this experiment" to “just give me a picture". Herein, we discuss the capabilities and resources at the beamline versus the needs of the industrial user. It is a rapidly evolving relationship with a bright future. Recent advances include grating-based phase contrast imaging, dynamic tomography, VisTrails workow, and Apple's iBook Authoring, with the last providing an informal, guided instruction for advanced topics in tomography.

Among several rendering techniques for volumetric data, direct volume rendering is a powerful visualization tool for a wide variety of applications. This paper describes the major features of hardware based volume exploration and presentation tool - Drishti. The word, Drishti, stands for vision or insight in Sanskrit, an ancient Indian language. Drishti is a cross-platform open-source volume rendering system that delivers high quality, state of the art renderings. The features in Drishti include, though not limited to, production quality rendering, volume sculpting, multi-resolution zooming, transfer function blending, profile generation, measurement tools, mesh generation, stereo/anaglyph/crosseye renderings. Ultimately, Drishti provides an intuitive and powerful interface for choreographing animations.

4D spatiotemporal images can be naturally divided into the background component, which is temporally coherent, and the motion component, which is spatially sparse, up to the proper basis. And this divide-and-conquer decomposition is an effective sparse representation of 4D images for the purpose of image reconstruction. Based on this prior fact, we introduce Prior Rank, Intensity and Sparsity Model (PRISM): the temporal coherence of the background component is enforced by the rank regularization and the spatial sparsity of the motion component is promoted by the sparsity regularization. In particular, the framelet based PRISM with the multi-resolution and multi-filtered structure will be utilized for image reconstruction. The superior performance of PRISM will be demonstrated with a few new medical imaging applications, including 4D cone beam CT, spiral MRI, and fused MRI-CT multi-modality.

In order to detect deformations of parts during the operating test, a novel dynamic industry computed tomography (ICT) system taking advantage of the rotation of specimens itself was purposed by us. However the stationary parts such as the shell around the turbine tips, which are hardly removed due to some industrial reasons, contaminate the projection data, so the blocks are not easily corrected from the projections as what we did in the traditional detector correction procedure. In this work, an interaction based CT reconstruction algorithm is purposed to deal the problem. First of all, we directly reconstruct the image with the contaminated projection data and an interactive match between the reconstructed image and the prior image is performed according to some obvious features. Then a forward-projection of the matched prior image with the practical geometric parameters is made. The block components in the projection data are estimated by calculating the average difference between the forward projections and the real projections of certain detectors. Finally, a new image can be reconstructed using the corrected data. Furthermore, the efficiency of the purposed algorithm is proved by both numerical simulation and practical experiments.

Despite impressive advancements in computed tomography (CT) technology in recent years, there are still critical and immediate needs in cardiac CT in terms of high spatial resolution, high temporal resolution and low radiation dose. Because carbon nanotube (CNT) x-ray sources can be compactly integrated, this technology can be used for multisource or stationary system to improve temporal resolution. To avoid the rotation of x-ray source, a lot of source-detector pairs are needed in a stationary CNT-based x-ray system. Limited by the space and costs, the number of source-detector pairs could not be too large, which results in a few-view scan problem. The reconstruction can be modeled as a l₁-norm minimization problem, which usually can be solved by compressive sensing (CS) based algorithms. To evaluate the data completeness of candidate next generation cardiac CT architectures with CNT x-ray source, based on the fact that smaller restricted isometry property (RIP) constants lead to a better l₁-norm recovery, we construct a measurement related to the RIP constants. The results show that the proposed RIP-based evaluation method coincides with the known CT reconstruction theory. This method is simple and easy to be implemented for different CT scan architectures, and it provides a practical tool to evaluate the data completeness in the framework of l₁-norm recovery theory without a specific CS-based reconstruction algorithm.

In this article, a cone-beam CT scanning mode is designed assuming four x-ray sources and a spherical sample. The x-ray sources are mounted at the vertices of a regular tetrahedron. On the circumsphere of the tetrahedron, four detection panels are mounted opposite to each vertex. To avoid x-ray interference, the largest half angle of each x-ray cone beam is 27°22', while the radius of the largest ball fully covered by all the cone beams is 0.460, when the radius of the circumsphere is 1. Several scanning schemes are proposed which consist of two rotations about orthogonal axes, such that each quarter turn provides sufficient data for theoretically exact and stable reconstruction. This design can be used in biomedical or industrial settings, such as when a sequence of reconstructions of an object is desired. Similar scanning schemes based on other regular or irregular polyhedra and various rotation speeds are also discussed.

X-ray phase contrast imaging (PCI) can provide high sensitivity of weakly absorbing low-Z objects in medical and biological fields, especially in mammography. Grating-based differential phase contrast (DPC) method is the most potential PCI method for clinic applications because it can works well with conventional X-ray tube and it can retrieve attenuation, DPC and dark-field information of the samples in a single scanning. Three kinds of information have different details and contrast which represent different physical characteristics of X-rays with matters. Hence, image fusion can show the most desirable characteristics of each image. In this paper, we proposed a multi-scale image fusion for X-ray grating-based DPC mammography. Firstly, non-local means method is adopted for denoising due to the strong noise, especially for DPC and dark-field images. Then, Laplacian pyramid is used for multi-scale image fusion. The principal component analysis (PCA) method is used on the high frequency part and the spatial frequency method is used on the low frequency part. Finally, the fused image is obtained by inverse Laplacian pyramid transform. Our algorithm is validated by experiments. The experiments were performed on mammoDPC instrumentation at the Paul Scherrer Institut in Villigen, Switzerland. The results show that our algorithm can significantly show the advantages of three kinds of information in the fused image, which is very helpful for the breast cancer diagnosis.

Current cardiac computed tomography (CT) is not fast enough for high or irregular heart rates, and the high radiation dose from cardiac CT scans remains a public concern. The primary cause of those unsatisfactory performances is the current CT architecture, in which one or two x-ray tubes need to be mechanically spun around an object to collect projection images, and x-ray beams need to be wide enough to cover the entire transaxial extent of an object without truncation. Here we present a new cardiac CT architecture. The new architecture features three distributed x-ray sources and three x-ray detectors. The three sources are stationary, with each containing an array of about 100 x-ray beams. The three detectors are rotating, and simultaneously acquire truncated projection data for the same interior region-of-interest. In synchrony with the rotating detectors, the three source arrays are electronically activated to simulate the spinning of three traditional single-beam x-ray sources. By estimate, the new architecture is expected to provide ≤50ms temporal resolution and ≤1mSv radiation dose.

This paper is motivated by our groups recent move from a conventional micro-CT system with a circular source-trajectory, to that with with a helical source-trajectory. By using a helix we can now image well beyond the limiting cone-angle of 10 degrees for a circle. We routinely perform micro-CT with cone-angles greater than 50° by using the Katsevich theoretically-exact reconstruction algorithm. Imaging with such large cone-angles enables high-signal-to-noise-ratio imaging but requires the specimen to be in a very close proximity to the source. This brings about its own challenges. Here we present experimental considerations and data post-processing techniques that allow us to obtain high-fidelity high-resolution micro-CT images at extreme cone-angles.

In our dual-modality microCT/microXRF system, the two sub-systems are combined in one machine, sharing a travelling sample holder. The microXRF, based on a pin-hole collimator and a photon-counting energysensitive 2D-detector, obtains 3D chemical composition maps of a sample. These images often lack structural information. With the built-in microCT, 3D structural information of the sample can be obtained. The two subsystems need to be properly calibrated and aligned. This calibration and alignment procedure needs to be done for all pin-hole collimators, but only need to be performed once after the system is assembled. The two modalities are calibrated separately, by analyzing projection images of a 3-ball phantom. The phantom is made of a very thin plastic cylinder, on which 3 copper balls are attached at well-chosen locations. The same phantom is used for both sub-systems and is scanned sequentially. We have evaluated this calibration method on various CT scanners and it has proven to be very effective. But it is more challenging for the XRF subsystem due to the strong absorptions. The two imaging spaces are calibrated relative to their own coordinate systems. To align the two sub-systems, the centers of the balls in reconstructed volumes are determined and then aligned using a rigid transformation. Repeated tests have shown that the mechanical movements are stable and the reconstructed image volumes can be well co-registered.

X-ray scatter can cause significant distortion in CT imaging, especially with the move to cone-beam geometries. Incoherent scatter (Compton scatter) is known to reduce the energy of scattered photons according to the angle of the scattering. The emergence of energy-resolved x-ray detectors offers an opportunity to produce and apply more accurate scatter estimates, leading to improved image quality. We have developed a scatter estimation algorithm that accounts for the variation in scatter with incident radiation energy. Where existing methods generate estimates of scatter for the complete detected energy band, our new method produces separate estimates for each of the energy bands that are measured, allowing a more focused correction of scatter. Our method is intended to be used in an iterative compensation framework like that of Rührnschopf and Klingenbeck (2011); it calculates the scatter contribution to each energy bin used in a scan based on the current volume estimate. Comparisons with Monte Carlo simulations indicate that this algorithm is effective at estimating the scatter level in separate energy bins. We found that the amount of scatter that loses enough energy to hop between energy bands is small enough to neglect, but that scatter intensity is dependent on the incident energy, so application of a spectrally-aware compensation technique is valuable.

The application of industrial CT covers many orders of magnitude of object sizes, ranging from freight containers (few meters) down to liquid foams (i.e. for food industry) or even parts of insects which are only several hundreds of micrometers in size. Similarly, the specifications for acquisition speed extend over some orders of magnitude, from hours to sub-second CT. We present the current technology in terms of X-ray sources and detectors, along with numerous applications from industry and materials research: e.g. industrial high-speed CT of car pistons, in situ micro-CT of milk foam decay at micrometer spatial resolution and 8 s scan time, as well as ex situ scans of tensile tested Nickel-alloys. The Fraunhofer Development Center X-ray Technology (Fürth, Germany) and the Chair of X-ray Microscopy (University Würzburg, Germany) are currently working on extending the technological limits, demonstrated, e,g. by the development of advanced X-ray detectors or a new inhouse CT system which comprises a high-brilliance liquid metal jet anode.

The X-ray micro-Tomography Facility at the Advanced Light Source has been in operation since 2004. The source is a superconducting bend magnet of critical energy 11.5 keV; photon energy coverage is 8-45 KeV in monochromatic mode, and a filtered white light option yields useful photons up to 50 keV. A user-friendly graphical user interface allows users to collect tomographic and radiographic data sets with options including tiled and time series data sets. We will focus on recent projects that utilize sample environments for in-situ imaging. These environments include a high pressure triaxial flow cell which has allowed study of supercritical CO2 transport through brine-saturated sandstone at pressures typical of in-situ conditions for subsurface CO2 sequestration and water transportation within live plants.

While classic CT theory targets exact reconstruction of a whole cross-section or an entire object, practical applications often focus on a region of interest (ROI). The long-standing interior problem is well known that an internal ROI cannot be exactly reconstruct only from truncated projection data associated with x-rays through the ROI. Although lambda tomography was developed to target gradient-like features of an internal ROI for the interior problem, it has not been well accepted in the biomedical community. On the other hand, approximate local reconstruction methods are subject to biases and artifacts. Recently, the interior problem is re-visited with appropriate prior knowledge, delivering practical results. First, the interior problem can be exactly and stably solved if a sub-region in an ROI is known. Thereafter, the sub-region knowledge can be replaced by certain rather weak constraints. For local reconstruction, a candidate image can be represented as the sum of the truth and an ambiguity component. Very surprisingly, the ROI image is prove to be the unique minimizer of the total variation (TV) or high order total variation (HOT) functional subject to the measurement, if the ROI is piece-wise constant or polynomial. Interior tomography algorithms based on HOT minimization have been developed for x-ray CT, and then extended for interior SPECT and interior differential phasecontrast tomography, respectively. In this paper, we will summarize the main theoretical and algorithmic results.

This work gives a new Compressed Sensing (CS) based Computed Tomography (CT) reconstruction method for limited angle problem. Currently CS based reconstruction methods are achieved by a minimizing process on the total variation (TV) of CT image under data consistency constraint. For limited-angle problem due to the missing range of projection views the strength of data consistency constraint becomes direction relevant. In our work a new anisotropic total variation (ATV) minimization method is proposed. Instead of using image TV as the minimization objective, an ATV objective is designed which is combined of multiple 1D directional TV with different weights according to the actual scanned angular range. Experiments with simulated data demonstrate the advantages of our approach relative to the standard CS based reconstruction methods.

We address the problem of tomographic image quality degradation due to the effects of beam hardening when using a polychromatic X-ray source. Beam hardening refers to the preferential attenuation of low-energy (or soft) X-rays resulting in a beam with a higher average energy (i.e., harder). In projection images, thin or low-Z materials appear more dense relative to thick or higher-Z materials. This misrepresentaion produces artifacts in the reconstructed image such as cupping and streaking.

Our method involves a post-acquisition software correction that applies a beam-hardening correction curve to remap the linearised projection intensities. The curve is modelled by an eighth-order polynomial and assumes an average material for the object. The process to determine the best correction curve requires precisely 8 reconstructions and re-projections of the experiment data. The best correction curve is defined as that which generates a projection set p that minimises the reprojection distance. Reprojection distance is defined as the L₂ norm of the difference between p, a set of projections, and RR†p, the result after p is reconstructed and then reprojected, i.e., ║RR†p − p║₂. Here R denotes the projection operator and R† is its Moore-Penrose pseudoinverse, i.e., the reconstruction operator.

This technique was designed for single-material objects and in this case the calculated curve matches that determined experimentally. However, this technique works very well for multiple-material objects where the resulting curve is a kind of average of all materials present. We show that this technique corrects for both cupping and streaking in tomographic images by including several experimental examples. Note that this correction method requires no knowledge of the X-ray spectrum or materials present and can therefore be applied to old data sets.

Nowadays a famous way to solve Computed Tomography (CT) inverse problems is to consider a constrained minimization problem following the Compressed Sensing (CS) theory. The CS theory proves the possibility of sparse signal recovery using under sampled measurements which gives a powerful tool for CT problems that have incomplete measurements or contain heavy noise. Among current CS reconstruction methods, one widely accepted reconstruction framework is to perform a total variation (TV) minimization process and a data fidelity constraint process in an alternative way by two separate iteration loops. However because the two processes are done independently certain misbalance may occur which leads to either over-smoothed or noisy reconstructions. Moreover, such misbalance is usually difficult to adjust as it varies according to the scanning objects and protocols. In our work we try to make good balance between the minimization and the constraint processes by estimating the variance of image noise. First, considering that the noise of projection data follows a Poisson distribution, the Anscombe transform (AT) and its inversion is utilized to calculate the unbiased variance of the projections. Second, an estimation of image noise is given through a noise transform model from projections to the image. Finally a modified CS reconstruction method is proposed which guarantees the desired variance on the reconstructed image thus prevents the block-wising or over-noised caused by misbalanced constrained minimizations. Results show the advantage in both image quality and convergence speed.

Sea urchins (Echinodermata: Echinoidea) generally possess an intricate jaw apparatus that incorporates five teeth. Although echinoid teeth consist of calcite, their complex internal design results in biomechanical properties far superior to those of inorganic forms of the constituent material. While the individual elements (or microstructure) of echinoid teeth provide general insight into processes of biomineralization, the cross-sectional shape (or macrostructure) of echinoid teeth is useful for phylogenetic and biomechanical inferences. However, studies of sea urchin tooth macro- and microstructure have traditionally been limited to a few readily available species, effectively disregarding a potentially high degree of structural diversity that could be informative in a number of ways. Having scanned numerous sea urchin species using micro-computed tomography µCT) and synchrotron µCT, we report a large variation in macro- and microstructure of sea urchin teeth. In addition, we describe aberrant tooth shapes and apply 3D visualization protocols that permit accelerated visual access to the complex microstructure of sea urchin teeth. Our broad survey identifies key taxa for further in-depth study and integrates previously assembled data on fossil species into a more comprehensive systematic analysis of sea urchin teeth. In order to circumvent the imprecise, word-based description of tooth shape, we introduce shape analysis algorithms that will permit the numerical and therefore more objective description of tooth macrostructure. Finally, we discuss how synchrotron µCT datasets permit virtual models of tooth microstructure to be generated as well as the simulation of tooth mechanics based on finite element modeling.

Direct examination of natural and engineered environments has revealed that the majority of microorganisms in these systems live in structured communities termed biofilms. To gain a better understanding for how biofilms function and interact with their local environment, fundamental capabilities for enhanced visualization, compositional analysis, and functional characterization of biofilms are needed. For pore-scale and community-scale analysis (100’s of nm to 10’s of microns), a variety of surface tools are available. However, understanding biofilm structure in complex three-dimensional (3-D) environments is considerably more difficult. X-ray microtomography can reveal a biofilm’s internal structure, but obtaining sufficient contrast to image low atomic number (Z) biological material against a higher-Z substrate makes detecting biofilms difficult. Here we present results imaging Shewanella oneidensis biofilms on a Hollow-fiber Membrane Biofilm Reactor (HfMBR), using the x-ray microtomography system at sector 2-BM of the Advanced Photon Source (APS), at energies ranging from 12.9-15.4 keV and pixel sizes of 0.7 and 1.3 μm/pixel. We examine the use of osmium (Os) as a contrast agent to enhance biofilm visibility and demonstrate that staining improves imaging of hydrated biofilms. We also present results using a Talbot interferometer to provide phase and scatter contrast information in addition to absorption. Talbot interferometry allows imaging of unstained hydrated biofilms with phase contrast, while absorption contrast primarily highlights edges and scatter contrast provides little information. However, the gratings used here limit the spatial resolution to no finer than 2 μm, which hinders the ability to detect small features. Future studies at higher resolution or higher Talbot order for greater sensitivity to density variations may improve imaging.

A novel system to image and reconstruct a 3-dimensional map of the refractive index based on the diffraction of light through a transparent sample is presented. This method is tested and validated on computer-generated data sets. The proposed system is an advanced variation of an imaging technique used in engineering for the study of aerodynamics. This method, which is termed Reference Image Topography, is used to reconstruct the water/air interface of the free surface in fluid dynamics studies. This surface profile is reconstructed by comparing an image of a random pattern viewed through the transparent free surface against a reference image, to determine the change in the refractive index caused by changes in the height. The proposed system is highly sensitive and capable of imaging intricate features in the transparent sample that are of low contrast when imaged with other imaging methods. For each projection, the change in direction of the light passing through the sample when placed in between the light source and the imaging system, can be related to the line integral for the change in refractive index across the sample. Utilizing multiple projections, a 3- dimensional map of the refractive index of the sample is reconstructed with computed tomography.

Multi-segment straight-line trajectory computed tomography (CT) requires accurate movement between each segment trajectories. In industrial applications for large objects, it is difficult and very cost-expensive for the mechanical and control system to ensure the accurate movement during the rotation process between two segment trajectories. Hence, precisely measuring the movement would be an alternative choice to acquire an exact reconstruction. In this work, we proposes a new method to measure the movement by using invariant moment of attenuation distribution images. Its accuracy improves as the number of projection data increases. The method is validated by both numerical and practical experiments. Reasonable CT reconstructions are obtained for a two-segment linear trajectory CT with coarse mechanical movement control modeled in our experiments.

Tomographic Gamma Scanning (TGS) is one of the non-destructive analysis technologies based on the principles of Emission Computed Tomography (ECT). Dedicated on imaging of the Gamma ray emission, TGS reveals radioactivity distributions for different radionuclides inside target objects such as nuclear waste barrels. Due to the special characteristics of TGS imaging geometry, namely, the relatively larger detector cell size and more remarkable view change in the imaging region, the line integral projection model widely used in ECT problems is no longer applicable for the radioactive intensity image reconstruction in TGS. The alternative Monte-Carlo based methods which calculate the detection efficiency at every detecting position for each voxel are effective and accurate, however time consuming. In this paper, we consider the geometrical detection efficiency of detector that is dependent on the detector-voxel relative position independently from the intrinsic detection efficiency. Further, a new geometrical correction method is proposed, where the voxel volume within the detector view is applied as the projection weight substituting the track length used in line integral model. And the geometrical detection efficiencies at different positions are analytically expressed by the volume integral on the voxel of geometrical point-source response function of the detector. Numerical simulations are taken and discussions are provided. The results show that the proposed method reduces the reconstruction errors compared to the line integral projection method while gaining better calculating efficiency and flexibility than former Monte-Carlo methods.

The Poisson-like noise model has been widely used for noise suppression and image reconstruction in low dose computed tomography. Various noise estimation and suppression approaches have been developed and studied to enhance the image quality. Among them, the recently proposed generalized Anscombe transform (GAT) has been utilized to stabilize the variance of Poisson-Gaussian noise. In this paper, we present a variance estimation approach using GAT. After the transform, the projection data is denoised conventionally with an assumption that the noise variance is uniformly equals to 1. The difference of the original and the denoised projection is treated as pure noise and the global variance σ² can be estimated from the residual difference. Thus, the final denoising step with the estimated σ² is performed. The proposed approach is verified on a cone-beam CT system and demonstrated to obtain a more accurate estimation of the actual parameter. We also examine FBP algorithm with the two-step noise suppression in the projection domain using the estimated noise variance. Reconstruction results with simulated and practical projection data suggest that the presented approach could be effective in practical imaging applications.

Impact-source X-ray microtomography (XMT) is a widely-used benchtop alternative to synchrotron radiation microtomography. Since X-rays from a tube are polychromatic, however, greyscale ‘beam hardening' artefacts are produced by the preferential absorption of low-energy photons in the beam path.

A multi-material ‘carousel' test piece was developed to offer a wider range of X-ray attenuations from well-characterised filters than single-material step wedges can produce practically, and optimization software was developed to produce a beam hardening correction by use of the Nelder-Mead optimization method, tuned for specimens composed of other materials (such as hydroxyapatite [HA] or barium for dental applications.) The carousel test piece produced calibration polynomials reliably and with a significantly smaller discrepancy between the calculated and measured attenuations than the calibration step wedge previously in use.

An immersion tank was constructed and used to simplify multi-material samples in order to negate the beam hardening effect of low atomic number materials within the specimen when measuring mineral concentration of higher-Z regions. When scanned in water at an acceleration voltage of 90 kV a Scanco AG hydroxyapatite / poly(methyl methacrylate) calibration phantom closely approximates a single-material system, producing accurate hydroxyapatite concentration measurements. This system can then be corrected for beam hardening for the material of interest.

X-ray luggage CT is widely used in airports and railway stations for the purpose of detecting contrabands and dangerous goods that may be potential threaten to public safety, playing an important role in homeland security. An X-ray luggage CT is usually in a helical trajectory with a high pitch for achieving a high passing speed of the luggage. The disadvantage of high pitch is that conventional filtered back-projection (FBP) requires a very large slice thickness, leading to bad axial resolution and helical artifacts. Especially when severe data inconsistencies are present in the z-direction, like the ends of a scanning object, the partial volume effect leads to inaccuracy value and may cause a wrong identification. In this paper, an iterative reconstruction method is developed to improve the image quality and accuracy for a large-spacing multi-detector high-pitch helical luggage CT system. In this method, the slice thickness is set to be much smaller than the pitch. Each slice involves projection data collected in a rather small angular range, being an ill-conditioned limited-angle problem. Firstly a low-resolution reconstruction is employed to obtain images, which are used as prior images in the following process. Then iterative reconstruction is performed to obtain high-resolution images. This method enables a high volume coverage speed and a thin reconstruction slice for the helical luggage CT. We validate this method with data collected in a commercial X-ray luggage CT.

Grating-based phase-contrast imaging has been a hot topic for several years owing to its excellent ability to discern lowdensity materials. Compared with commercial X-ray computed tomography (CT) systems, the ‘phase-stepping’ motion in grating-based phase-contrast CT (GPC-CT) takes too long to implement in a CT scan. Additionally, the radiation dose delivered to the sample is several times that delivered by a conventional CT scan. In this paper, we compared four kinds of scanning schemes for GPC-CT and pointed out their advantages and limitations for clinical applications. Following the interlaced phase stepping method, we proposed a novel reconstruction method, namely the inner-focusing reconstruction method. With the proposed method, the gratings can be easily integrated into a conventional CT system implementing phase-contrast imaging with a complete field-of-view. Numerical experiments verified the effectiveness of the proposed method in achieving fast and low-dose GPC-CT.

We study reconstruction methods and imaging properties of the circular and helical interlaced source-detector array (ISDA) computed tomography (CT) system. The system uses carbon nanotube (CNT) based field emission X-ray source arrays and detector arrays. Distributed sources and detectors allow projection data been acquired from different direction by switching on the X-ray sources sequentially, requiring no rotation of gantry or object. Thus the system enables high temporal resolution and eliminates motion artifacts caused by gantry rotation as is common in the conventional CT systems. Interpolation is implemented to patch the absent data in the projection image, and tilted plane Feldkamp type reconstruction algorithm (TPFR) is used to reduce the cone beam artifacts for helical ISDA CT. We analyze the distribution of artifacts in the reconstruction, as well as the influence of the detector array gap and the helix pitch on reconstruction quality. Simulation studies demonstrate that the gap ratio is the key factor on the artifacts due to the gap, and increasing the pitch will reduced gap ratio. Choosing the helix pitch appropriately by getting a balance between cone beam artifacts and gap induced artifacts can get a better reconstruction.

Crown and bridge restorations are one of the main treatment methods in fixed prosthodontics. The fabrication requires data on the patient’s denture shape. This information is generally obtained as a hard copy from an impression mold. Alternatively, one can acquire the data electronically using oral optical three-dimensional (3D) imaging techniques, which determine the surface of the denture. The aim of the study was to quantitatively compare the accuracy of three dimensional scanning with that of conventional impressions and give a statement how far the scanner provides a clinical alternative with equal or better precision. Data from 10 teeth were acquired in the dental office with a polyether impression material and an oral scanner. Data from the impressions were digitalized by means of micro computed tomography. The data were then 3D registered to identify the potential differences between impression and optical scan. We could demonstrate that the oral scanner’s data and the conventional impressions are comparable.

The production of dental inlays and crowns requires precise information on patients’ teeth morphology. The conventional method is the preparation of impressions using mold materials, e.g. a silicone impression material. The disadvantage of this technique is the human choke impulse and the flavor of the material. These discomforts can be avoided by methods where a three-dimensional scanner is used for recording the teeth morphology. The present study reveals the accuracy of three model types, namely conventional impression, rapid prototyping using an oral scanner C.O.S., 3M (Schweiz) AG and milling from a proprietary resin using the oral scanner iTero, Straumann Holding AG. For each method five models were fabricated from a steel reference (standard). Using a nanotom m (phoenixǀx-ray, GE Sensing and Inspection Technologies GmbH), three-dimensional micro computed tomography data sets of the standard and the 15 models were recorded and landmark distances within the data sets were measured with sub-pixel accuracy. To verify these results a coordinate measuring machine (Leitz PMM 864, Hexagon Metrology GmbH) based on tactile detection was used for the measurement of the landmark distances, and a correction of the distances measured by the nanotom m was arranged. The nanotom data sets of the 15 models were also compared to the standard by means of a non-rigid registration algorithm. The calculated deformation field exhibited mean pixel displacement values of (0.19 ± 0.09) mm for the C.O.S. models, (0.12 ± 0.07) mm for the gypsum models and (0.19 ± 0.12) mm for the i-Tero models.

To utilize the synergy between CT and MR datasets from an object at the same time, a unified dual-modality image reconstruction approach is proposed using a dual-dictionary learning technique. The key is to establish a knowledgebased connection between these two datasets for a tight fusion of different imaging modalities. Our scheme consists of three inter-related elements: dual-dictionary learning, CT image reconstruction, and MR image reconstruction. Our experiments show that even with highly under-sampled MR data and few x-ray projections, we can still satisfactorily reconstruct both MR and CT images. This approach can be potentially useful for a CT-MRI system.

Multiple-source structure is promising in the development of computed tomography, for it could effectively eliminate motion artifacts in the cardiac scanning and other time-critical implementations with high temporal resolution. However, concerns about the dose performance shade this technique, as few reports on the evaluation of dose performance of multiple-source CT have been proposed for judgment. Our experiments focus on the dose performance of one specific multiple-source CT geometry, the triple-source CT scanner, whose theories and implementations have already been well-established and testified by our previous work. We have modeled the triple-source CT geometry with the help of EGSnrc Monte Carlo radiation transport code system, and simulated the CT examinations of a digital chest phantom with our modified version of the software, using x-ray spectrum according to the data of physical tube. Single-source CT geometry is also estimated and tested for evaluation and comparison. Absorbed dose of each organ is calculated according to its real physics characteristics. Results show that the absorbed radiation dose of organs with the triple-source CT is almost equal to that with the single-source CT system. As the advantage of temporal resolution, the triple-source CT would be a better choice in the x-ray cardiac examination.

A scheme is proposed here for spectrography that is for 3D analysis of an object from a single spectral view. In this scheme, we first reconstruct some planes that go through the origin of the Fourier space and interact significantly with Ewald spheres. Since only amplitude data are measured, the corresponding phase information is estimated using a hybrid-input-output algorithm. Finally, each of the specified planes is reconstructed from the highly under-sampled Fourier data using a dictionary learning technique. According to the Fourier central slice theorem, the reconstructed image is equivalent to a parallel-beam projection of the object. Hence, the reconstructed projections can be used to analyze internal structures of the object via stereo imaging. The numerical experiments suggest that our method is promising for studies on 3D structures from one spectral view.

Recently, ‘ankylography’ was proposed to perform a 3D reconstruction from a single exposure of a monochromatic radiation beam. This approach appeared very attractive to reveal structures of important objects such as complex proteins that can be glimpsed only once before they are destroyed by a high-intensity x-ray laser beam. However, this approach does not give a unique solution and is highly unstable when the number of voxels is not too small. In this paper, we acquire one or two polychromatic diffractive views with energy-sensitive detectors simultaneously. Specifically, a spectrography system may consist of two spectral coherent imaging chains perpendicular to each other. As a result, multiple Ewald spheres of different radii can be simultaneously measured in the Fourier space, and an image volume can be practically reconstructed. To evaluate the performance of spectrography, the hybrid input-output algorithm is implemented for phase retrieval and improved with a lower dimensional subspace saddle-point optimization technique proposed by Marchesini. For different configurations of the proposed spectrography scheme, extensive numerical tests are conducted, yielding encouraging results.