Micro-CT, with voxel size ~10^-5 mm³, has a great advantage over traditional microscopic methods in its ability to generate detailed 3D images in relatively large, opaque, volumes such as an intact mouse femur, heart or kidney. In addition to providing new insights into tissue structure-to-function interrelationships, micro-CT can contribute to suggesting new applications of clinical CT imaging such as: A. The spatio-density-temporal resolution that is needed to: 1) Quantitate an organ's Basic Functional Unit (smallest collection of diverse cells that behaves like the organ), which requires voxels less than 10^-4 mm³ in volume; 2) Quantitate new vessel growth which manifests as increased x-ray contrast enhancement in tissues during passage of a bolus of intravascular contrast agent; 3) Quantitate endothelial integrity by the movement of x-ray contrast agents across the endothelial inner lining of vessel walls. B. The use of x-ray scatter for providing the contrast amongst soft tissue components and/or their interfaces for enhanced discrimination of nerve and muscular/tendon fiber directions.

The microstructure of brain tissues becomes visible using different types of optical microscopy after the tissue sectioning. This preparation procedure introduces stress and strain in the anisotropic and inhomogeneous soft tissue slices, which are several 10 μm thick. Consequently, the three-dimensional dataset, generated out of the two-dimensional images with lateral submicrometer resolution, needs algorithms to correct the deformations, which can be significant for mellow tissue such as brain segments. The spatial resolution perpendicular to the slices is much worse with respect to the lateral sub-micrometer resolution. Therefore, we propose as complementary method the synchrotron-radiation-based micro computed tomography (SRμCT), which avoids any kind of preparation artifacts due to sectioning and histological processing and yields true micrometer resolution in the three orthogonal directions. The visualization of soft matter by the use of SRμCT, however, is often based on elaborate staining protocols, since the tissue exhibits (almost) the same x-ray absorption as the surrounding medium. Therefore, it is unexpected that human tissue from the pons and the medulla oblongata in phosphate buffer show several features such as the blood vessels and the inferior olivary nucleus without staining. The value of these tomograms lies especially in the precise non-rigid registration of the different sets of histological slices. Applications of this method to larger pieces of brain tissue, such as the human thalamus are planned in the context of stereotactic functional neurosurgery.

In this study the structure of the adult human dentoalveolar process is examined using conventional and synchrotron radiation-based microtomography (SRμCT). Mandibular and maxillary segments containing two to five adjacent teeth were harvested at autopsy from 49 adult donors. These segments were embedded in blocks of methylmetacrylate and scanned using a conventional table-top μCT-scanner at a pixel size and slice thickness of 35 μm. A few segments were also scanned at a synchrotron facility at an initial pixel size of 16.4 μm, which was binned by a factor 2 to result in an effective voxel size of almost 32.8 μm. The three-dimensional reconstructions revealed how intricately the teeth are supported by the alveolar bone. Furthermore, this support is highly inhomogeneous with respect to the buccal, mesial, lingual and distal quadrants. Reflecting their various degrees of mineralization, tissues like bone, dentine, enamel and cementum, could well be identified, especially in the scans made with SRμCT. Despite comparable voxel sizes, the reconstructed data-sets obtained with conventional μCT were less detailed and somewhat fuzzy in appearance compared to the data-sets of SRμCT. However, for quantification of macroscopical features like the thickness of the alveolar wall or the presence of dehiscences/fenestrations this seemed sufficient.

Diseases of the hearing organ and impairment affect a significant fraction of population. Therefore, the hearing organ embedded as a helical structure in the cochlea within the hardest human osseous structure inside the petrous bone is intensively investigated. Currently, studies of the cochlea with true micrometer resolution or better are destructive. Membranes and three-dimensional vessel structures of post-mortem explanted human cochlea were only visualized with limited spatial resolution or deformed anatomical features resulting from preparation artifacts. We have applied a preparation and staining protocol developed for electron microscopy, which allows the visualization and quantification of a great variety of soft-tissue structures including the Reissner's membrane, the tectorial membrane, basilar membrane, modiolus, lamina radialis, and Nuel's space by the use of synchrotron-radiation-based micro computed tomography at the beamline BW 2 (HASYLAB at DESY). The level of detail can be even improved by the application of sophisticated computer vision tools, which enables the extraction of the vascular tree down to the capillaries and of the course of nerve fibers as well as the topology of the osseous lamina radialis, which assembles the nerve fibers from the hair-cells to the ganglia in the center of the cochlea, the modiolus. These non-destructively obtained three-dimensional data are principal for the refined understanding of the hearing process by membranes morphologies and further anatomical features at the cellular level and for teaching purposes in medical curricula.

Biodegradable metal implants for musculoskeletal and intravascular applications made of magnesium alloys have been shown to degrade in-vivo by corrosion. The in vivo corrosion of magnesium alloys has the potential to provide a new mechanism which will allow metal implants to be applied in musculoskeletal surgery as biodegradable implants. This would particularly be true if magnesium alloys with predictable in vivo corrosion rates could be developed. Since the magnesium corrosion process depends on the corrosive environment, the corrosion rates of magnesium alloys under standard in-vitro environmental conditions are not directly comparable to results obtained from an animal model. Synchrotron-radiation based microtomography (SRμCT) enabled us to investigate non-destructively the in vivo corrosion as well as the osteointegration at the implant-bone interphase at a high spatial resolution. Corrosion morphology and its metallurgical quantification of pit formation could be obtained. Since the alloying elements of magnesium alloys have significant importance for the degradation process in biological environments the biocompatibility depending on their local concentration and distribution has to be investigated. For this purpose we used element-specific SRμCT to show the spatial distribution without destroying the bone-implant interphase. The SRμCT setup at HASYLAB at DESY will be an excellent tool in the future to develop suitable magnesium alloys and magnesium implants for special medical applications.

The quantitative analysis of bone formation around biofunctionalised metallic implants is an important tool for the further development of implants with higher success rates. This is, nowadays, especially important in cases of additional diseases like diabetes or osteoporosis. Micro computed tomography (μCT), as non-destructive technique, offers the possibility for quantitative three-dimensional recording of bone close to the implant's surface with micrometer resolution, which is the range of the relevant bony structures. Within different animal models using cylindrical and screw-shaped Ti6Al4V implants we have compared visualization and quantitative analysis of newly formed bone by the use of synchrotron-radiation-based CT-systems in comparison with histological findings. The SRμCT experiments were performed at the beamline BW 5 (HASYLAB at DESY, Hamburg, Germany) and at the BAMline (BESSY, Berlin, Germany). For the experiments, PMMA-embedded samples were prepared with diameters of about 8 mm, which contain in the center the implant surrounded by the bony tissue. To (locally) quantify the bone formation, models were developed and optimized. The comparison of the results obtained by SRμCT and histology demonstrates the advantages and disadvantages of both approaches, although the bone formation values for the different biofunctionalized implants are identical within the error bars. SRμCT allows the clear identification of fully mineralized bone around the different titanium implants. As hundreds of virtual slices were easily generated for the individual samples, the quantification and interactive bone detection led to conclusions of high precision and statistical relevance. In this way, SRμCT in combination with interactive data analysis is proven to be more significant with respect to classical histology.

Micro-CT for bone structural analysis has progressed from an in-vitro laboratory technique to devices for in-vivo assessment of small animals and the peripheral human skeleton. Currently, topological parameters of bone architecture are the primary goals of analysis. Additional measurement of the density or degree of mineralization (DMB) of trabecular and cortical bone at the microscopic level is desirable to study effects of disease and treatment progress. This information is not commonly extracted because of the challenges of accurate measurement and calibration at the tissue level. To assess the accuracy of micro-CT DMB measurements in a realistic but controlled situation, we prepared bone-mimicking watery solutions at concentrations of 100 to 600 mg/cm3 K2PO4H and scanned them with micro-CT, both in glass vials and microcapillary tubes with inner diameters of 50, 100 and 150 mm to simulate trabecular thickness. Values of the linear attenuation coefficients m in the reconstructed image are commonly affected by beam hardening effects for larger samples and by partial volume effects for small volumes. We implemented an iterative reconstruction technique to reduce beam hardening. Partial voluming was sought to be reduced by excluding voxels near the tube wall. With these two measures, improvement on the constancy of the reconstructed voxel values and linearity with solution concentration could be observed to over 90% accuracy. However, since the expected change in real bone is small more measurements are needed to confirm that micro-CT can indeed be adapted to assess bone mineralization at the tissue level.

Rapid Prototyping and especially the 3D printing, allows generating complex porous ceramic scaffolds directly from powders. Furthermore, these technologies allow manufacturing patient-specific implants of centimeter size with an internal pore network to mimic bony structures including vascularization. Besides the biocompatibility properties of the base material, a high degree of open, interconnected porosity is crucial for the success of the synthetic bone graft. Pores with diameters between 100 and 500 μm are the prerequisite for vascularization to supply the cells with nutrients and oxygen, because simple diffusion transport is ineffective. The quantification of porosity on the macro-, micro-, and nanometer scale using well-established techniques such as Hg-porosimetry and electron microscopy is restricted. Alternatively, we have applied synchrotron-radiation-based micro computed tomography (SRμCT) to determine the porosity with high precision and to validate the macroscopic internal structure of the scaffold. We report on the difficulties in intensity-based segmentation for nanoporous materials but we also elucidate the power of SRμCT in the quantitative analysis of the pores at the different length scales.

Sea urchin spines protect the animal's body from predators and from the effect of high energy environments. The spines of urchins from different orders, families and genera have very different sizes, morphologies and microarchitectures, and the different designs of sea urchin spines reveal much about the design space available for functional biogenic calcite-based structures. The 3D microarchitecture of primary spines of a number of sea urchins was studied with synchrotron microCT and reconstructed with 5 μm or smaller voxels (volume elements), and similarities and differences were determined in order to better understand the design space. Hollow spines from different genera of the family Diadematidae, order Diadematoida, are one type of solution, but significant differences were observed within this phylogenic subset. Spines from members of order Echinoidea, family Toxopneustidae, employ a very different strategy, one that emphasizes interconnected trabeculae to a greater degree than do the diadematids. Numerical data for some 3D structural characteristics are presented, data that would be impractical to obtain by methods other than microCT.

The projection X-ray microscope utilized a very small X-ray source emitted from a thin (0.1-3 μm) target metal film excited by the focused electron beam of a scanning electron microscope (SEM). When an object is placed just below the target metal film, the diverging X-rays enlarge the shadow of the object. Because no X-ray optics such as a zone-plate is used, the focal depth is, in principle, infinitely large. We exploited this to apply projection X-ray microscopy to three-dimensional (3-D) structure analysis by means of cone-beam computed tomography (CT). A small arthropod (Pseudocneorhinus bifasciatus, 5 mm in length) was examined for CT study. The projection images were recorded at 3-degree increments over the whole range (360°) of a stepping-motor-controlled sample rotator. The 3-D reconstructed image was calculated to be 256 x 256 x 256 (5 μm) voxel data. The reconstructed 3-D image showed in detail the internal structure of an opaque object. Trial for element mapping using projection X-ray microscope is also performed by developing a new target exchanger. This apparatus enables exchange of metal targets without leaking vacuum of SEM. By taking images using Kα line from nickel and cobalt targets, distribution of iron, which has absorption edge between two Kα lines, can be shown. Distribution of less than 10 μm iron particles is distinguished from cobalt particles. This system would be applicable for 3-D element analysis.

To describe the different aspects of bone quality, we follow a hierarchical approach and assess bone tissue properties in different regimes of spatial resolution, beginning at the organ level and going down to cellular dimensions. For these purposes we developed different synchrotron radiation (SR) based computed-tomography (CT) methods to assess murine bone ultrastructure. In a first step, a tubular system and the osteocyte lacunar system within murine cortical bone have been established as novel ultrastructural quantitative traits. Results in two mouse strains showed that morphometry of these quantitative traits was dependent on strain and partially on gender, and that their scaling behavior with bone size was fundamentally different. In a second step, we explored bone competence on an ultrastructural level and related our findings to the two ultrastructural quantitative traits introduced before. We showed that SR CT imaging is a powerful tool to investigate the initiation and propagation of microcracks, which may alter bone quality and may lead to increased fracture risk by means of microdamage accumulation. In summary, investigation of ultrastructural bone tissue properties will eventually lead to a better understanding of bone quality and its relative contribution to bone competence.

Genetically similar white rabbits raised on diets of different mechanical properties, as well as wild-type and myostatin-deficient mice raised on similar diets, were compared to assess the postweaning effects of elevated masticatory loads due to increased jaw-adductor muscle and bite forces on the proportions and properties of the mandibular symphysis and temporomandibular joint (TMJ). Microcomputed tomography (microCT) was used to quantify bone structure at a series of equidistant external and internal sites in coronal sections for a series of joint locations. Discriminant function analyses and non-parametric ANOVAs were used to characterize variation in biomineralization within and between loading cohorts. In both species, long-term excessive loading results in larger joint proportions, thicker articular and cortical bone, and increased biomineralization of hard tissues. Such adaptive plasticity appears designed to maintain the postnatal integrity of masticatory joint systems for a primary loading environment(s). This behavioral signal may be increasingly mitigated in older organisms by the interplay between adaptive and degradative joint tissue responses.

The bioluminescence tomography (BLT) emerges as a novel molecular imaging technology for small animal studies. BLT is an ill-posed inverse source problem subject to Cauchy data of the diffusion model. Several algorithms were developed to regularize this problem. Although those algorithms produce encouraging results, they theoretically require the completely measured data on the external surface. In practice, the observed data is often incomplete due to physical limitations. The BLT problem in this situation is similar to limited angle X-ray CT although the imaging model is more complicated with BLT. In this work, we formulate a mathematical model for BLT from partial data and generalize our previous results on the solution uniqueness to the partial data case. Also, we extend our previous methods to handle incomplete data. The first method is a variant of the well-known EM algorithm. The second one is based on the Landweber scheme. Both methods allow incorporation of knowledge-based constraints. Numerical and physical phantoms are used to evaluate and validate the proposed algorithms.

Because of the importance of the so-called long object problem, spiral cone-beam computed tomography (CT) has become a hot area in the CT field since it was first proposed in 1991. As a main stream in the development of the next generation medical CT, spiral cone-beam CT has been greatly improved, especially in the aspect of image reconstruction methods. Now, the state-of-the-art cone-beam algorithms can reconstruct images exactly from longitudinally truncated data collected along a rather general scanning trajectory. Here we present a brief overview of this area with an emphasis on the results achieved by our team.

In this paper, we for the first time define the concept of 3D skew lambda tomography (SLT) based on the 3D Calderon Operator, and formulate an approximate local reconstruction algorithm for cone beam data collected along an arbitrary scanning curve. The main idea is to rewrite the filtering operator in an exact filtered-backprojection reconstruction formula as a local projection. While the practical cone-beam lambda tomography works well for spirals with small pitches, the proposed SLT is more suitable to the spirals with large pitch. Simulation using the 3D differentiable Shepp- Logan phantom is performed to demonstrate the utility of this new technique.

A typical X-ray CT scanner has a 50cm reconstruction field-of-view (FOV) which is significantly smaller than the 70cm FOV typically used for PET. When CT images are used for attenuation correction in PET, significant artifacts result when portions of the scanned object extend beyond 50 cm. In this paper, we present a reconstruction algorithm to estimate the missing projection samples so that a significantly larger reconstruction FOV can be achieved. The estimation is based on the observation that the total attenuation is a continuous function over views. The initial estimate of the projection distribution makes use of the property that the projection profile does not change abruptly as a function of the projection angle. When combined with the projection values at the location of truncation, the size and location of water cylinders that best fit these parameters are calculated. Additional adjustments are made to ensure the total attenuation of the expanded projection samples matches closely to the estimated total missing projection. The estimated projection is further blended with the mirror image of the measured projections near the location of truncation. Various phantom experiments were conducted to evaluate the proposed algorithm. Both axial and helical scans were collected on a 64-slice scanner. Results show that the proposed algorithm can restore the fidelity of the reconstruction for the portion of the object inside 50 cm FOV, and provide an adequate impression of the object outside 50cm.

Bioluminescence tomography (BLT) is a novel technique in vivo which may localize and quantify bioluminescent source to reveal the molecular and cellular information, and therefore it can monitor the growth and regression of tumor non-invasively. In complicated biological tissue, the accuracy improvement of numerical solution to the forward problem of BLT is beneficial to achieve better spatial resolution of source distribution. In this paper, we introduce the adaptive FEMs framework based on the diffusion equation to enhance the solution accuracy of the forward problem, and the bioluminescence imaging experiment has been performed with the heterogeneous physical phantom which is also scanned by microCT scanner to generate the volumetric mesh as the initial finite element mesh. Finally, The effectiveness of the adaptive FEMs framework is demonstrated with the comparison between the experimental results and the simulation solution.

A facility for x-ray computed microtomography (CMT) is operating as a national user facility for earth and environmental sciences research on the bending magnet beamline at the GeoSoilEnviroCARS sector at the Advanced Photon Source (APS). The APS bending magnet has a critical energy of 20 keV, and thus provides high flux at photon energies up to 100 keV, making it well suited to imaging a wide range of earth materials up to several cm in size. The beamline is equipped with a Si (111) double-crystal monochromator covering the energy range from 5 to 70 keV with beam sizes up to 50mm wide and 6mm high. The transmitted x-rays are imaged with a single crystal YAG or CdWO₄ scintillator, a microscope objective and a 1300x1030 pixel 12-bit 5MHz CCD detector. The maximum spatial resolution is under 1.5 μm in both the transmission radiographs and the reconstructed slices. Data collection times for full 3-D datasets range from 5-60 minutes. This facility has been used for a wide range of studies, including multiphase fluids in porous media, high-pressure studies, meteorites, and hyper-accumulating plants. We present recent technical improvements in the system, which include improved optics for samples larger than 5mm, significant reduction of ring artifacts, and correction of mechanical errors in the rotation stage.

X-ray microtomography is an established tool for three-dimensional (3D) imaging of thick structures at micron scale. The fast microtomography system developed at beamline 2-BM of the Advanced Photon Source (APS) offers near video-rate acquisition of tomographic data at micrometer spatial resolution, pipelined processing, and 3D visualization. At its maximum throughput, the system can image hundreds of specimens per day. Every sample is fully analyzed within 2-3 minutes, giving the user immediate feedback on the quality of the results. The entire instrument, including the tomography setup, automatic sample loader, beamline, and a dedicated 32-node computer cluster for data analysis, is also remotely accessible via Access Grid (AG) technology giving a user full remote control of every aspect of the experiment. During the last year the 2-BM microtomography system has been extensively used to resolve the density distribution of biological and material samples at micrometer spatial resolution. The final results are usually presented as a 3D volume or as slices. The quasi-real-time feature of the system has been instrumental in several applications in both biological applications, where a statistical approach is needed to characterize a broad population of samples, and in material science, where time-dependent 3D sample evolution can be studied on practical time scales. In this paper we present the current beamline status and the latest experimental results.

We have designed and commissioned an apparatus for serial crystallography of hydrated proteins at the Advanced Light Source. Serial crystallography is a recently proposed method of imaging uncrystallized proteins at a third generation synchrotron source. This paper describes the design of the apparatus and results from the first experiment, which recorded x-ray diffraction patterns from 8 micron droplets containing photosystem 1 protein molecules.

Synchrotron-based X-ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non-destructive, high-resolution investigations of a broad kind of materials. High-brilliance and high-coherence third generation synchrotron radiation facilities allow micrometer and sub-micrometer, quantitative, three-dimensional imaging within very short time and extend the traditional absorption imaging technique to edge-enhanced and phase-sensitive measurements. At the Swiss Light Source TOMCAT, a new beamline for TOmographic Microscopy and Coherent rAdiology experimenTs, has been recently built and started regular user operation in June 2006. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM) covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10^-4. The beamline can also be operated in white-beam mode, providing the ideal conditions for real-time coherent radiology. This article presents the beamline design, its optical components and the endstation. It further illustrates two recently developed phase contrast techniques and finally gives an overview of recent research topics which make intense use of SRXTM.

The methodical development and first instrumental implementation of computed laminography / tomosynthesis using synchrotron radiation are presented. The technique was developed for three-dimensional imaging of flat and laterally extended objects with high spatial resolution. This paper introduces the fundamental principle of the imaging process and discusses the method's particularities in comparison to computed tomography and computed laminography / digital tomosynthesis. Introducing a simple scanning geometry adapted to the particular experimental conditions of synchrotron imaging set-ups (such as the stationary source and a parallel beam) allows us to combine the advantages of laminography and those provided by synchrotron radiation, for instance monochromatic radiation in order to avoid beam hardening artefacts, high beam intensity for achieving high spatial resolution and fast scanning times or spatial coherence for exploiting phase contrast. The potential of the method for three-dimensional imaging of microelectronic devices is demonstrated by examples of flip-chip bonded and wire-bonded devices.

This paper describes a set of algorithms that enable virtually complete ring artifact removal from tomographic imagery with minimal to negligible contamination of the underlying data. These procedures were created specifically to deal with data as acquired at the University of Texas high-resolution X-ray CT facility, but are likely to be applicable in other settings as well. In most cases corrections are optimally applied to sinogram data before reconstruction, but a variant is developed for correcting already-reconstructed images. The algorithms make particular use of repetitive aspects of the artifact across images to improve behavior. However, fully utilizing this functionality requires processing entire data sets simultaneously, rather than one image at a time. A number of parameters may be adjusted to optimize results for particular data sets.

The tomographic images reconstructed from cone beam projection data with a slice thickness larger than the nominal detector row width (namely thick image) is of practical importance in clinical CT imaging, such as neuro- and trauma- applications as well as applications for treatment planning in image guided radiation therapy. To get a balance optimization between image quality and computational efficiency, a cone beam filtered backprojection (CB-FBP) algorithm to reconstruct a thick image by tracking adaptively up-sampled cone beam projection of virtual reconstruction planes is proposed in this paper. Theoretically, a thick image is a weighted summation of a number of images with slice thickness corresponding to the nominal detector row width (namely thin image), and each thin image corresponds to a virtual reconstruction plane. To obtain the most achievable computational efficiency, the weighted summation has to be carried out in projection domain. However, it has been experimentally found that, to obtain a thick image with the reconstruction accuracy comparable to that of a thin image, the CB-FBP reconstruction algorithm has to be applied by tracking adaptively up-sampled cone beam projection data, which is the novelty of the proposed algorithm. The tracking process is carried out by making use of the cone beam projection data corresponding to the involved virtual reconstruction planes only, while the adaptive up-sampling process is implemented by interpolation along the z-direction at an adequate up-sampling rate. By using a helical body phantom, the performance of the proposed cone beam reconstruction algorithm, particularly its capability of suppressing artifacts, are experimentally evaluated and verified.

Phase-contrast x-ray computed tomography (CT) is an emerging imaging technique that can be implemented at third generation synchrotron radiation sources or by using a microfocus x-ray tube. Promising experimental results have recently been obtained in material science and biological applications. At the same time, the lack of a mathematical theory comparable to that of conventional absorption-based CT limits the progress in this field. We suggest such a theory and prove a fundamental theorem that plays the same role for phase-contrast CT as the Fourier slice theorem does for absorption-based CT. The fundamental theorem allows us to derive fast image reconstruction algorithms in the form of filtered backprojection (FBP).

We have developed a quality function that quantifies how well features are reconstructed in 3D phase contrast tomographic reconstructions for pure phase samples. We consider image formation using the free space propagation method for each projected data-set. A partially coherent radiation field originating from an extended source is also incorporated. This means the model is suitable for a laboratory based micro focus x-ray source. The quality function is useful for optimizing the tomographic reconstruction for given feature sizes in an object. We then use the quality function to develop filters for improving the reconstruction quality for high spatial frequency objects.

The coherence requirements for efficient operation of an X-ray grating interferometer are discussed. It is shown how a Talbot-Lau geometry, in which an array of equidistant secondary sources is used, can be used to decouple fringe visibility in the interferometer (and thus, its efficiency) from the total size of the X-ray source. This principle can be used for phase-contrast radiography and tomography with sources of low brilliance, such as X-ray tubes.

An X-ray Talbot interferometer for X-ray phase imaging and tomography was constructed using an amplitude grating of a gold pattern 8 μm in pitch and 30 μm in height developed by X-ray lithography and gold electroplating. The effective area of the grating was 20 mm x 20 mm, and was fully illuminated by synchrotron radiation at beamline 20XU, SPring-8, Japan. Almost whole body of a fish 3 cm in length was observed by phase tomography. Resulting images obtained with 0.07 nm and 0.045 nm X-rays revealed organs with bones in the same view successfully. A preliminary result of the combination with an X-ray imaging microscope is also presented, which was attempted to attain a higher spatial resolution. Finally, prospects of the compatibility with a conventional X-ray generator are discussed for practical applications such as clinical diagnoses.

Propagation-based phase-contrast tomography is a coherent imaging method that seeks to reconstruct the three-dimensional complex-valued refractive index distribution of an object. Measurements of the transmitted wavefield intensities on two parallel detector-planes at each tomographic view angle are utilized to determine the wavefield's complex amplitude, which represent the projection data utilized for tomographic reconstruction. The mathematical formulas employed to determine the complex amplitude contain Fourier domain singularities that can result in greatly amplified noise levels in the reconstructed images. In this article, statistically optimal reconstruction methods that employ multiple (>2) detector-planes are developed that mitigate the noise amplification effects due to singularities in the reconstruction formulas. These reconstruction methods permit exploitation of statistically complementary information in a collection of in-line holographic measurement data, resulting in images that can have dramatically reduced noise levels. Computer-simulation studies are conducted to demonstrate and investigate quantitatively the developed reconstruction methods.

We perform a theoretical analysis of the mathematical stability and locality of several modes of amplitude and phase contrast computed tomography (CT) suitable for reconstruction of the 3D distribution of complex refractive index in samples displaying weak absorption contrast. We present a general formalism for CT reconstruction in linear shift-invariant optical systems. Examples of such systems include propagation-based and analyser-based CT. We obtain general formulae for CT reconstruction from analyser-based projection data. We also propose a new tomographic algorithm for the reconstruction of the 3D distribution of complex refractive index in a sample from a single propagation-based projection image per view angle, where the images display both absorption and phase contrast. The method assumes that the real and imaginary parts of the refractive index are proportional to each other. Using singular-value decompositions of the relevant operators we show that, in contrast to conventional amplitude-contrast CT, phase-contrast (diffraction) tomography is mathematically well-posed. The presented results are pertinent to biomedical imaging and non-destructive testing of samples exhibiting weak absorption contrast.

X-ray CT system with phase-contrast and fluorescent techniques are being developed for biomedical researches. We have applied these techniques for in-vivo and ex-vivo imaging. The phase-contrast x-ray CT enables to reveal the detailed morphological information of cancer lesion, and image quality of ex-vivo specimen was excellent comparing to 4.74T micro-MRI. Fluorescent x-ray CT could depict the functional information with high spatial resolution, and its image quality was almost the same as autoradiogram. Improvement of imaging system with much high-speed data acquisition will enable to use these techniques for new biomedical researches.

In this work, we continue to pursue penalized-likelihood image reconstruction algorithms for X-ray fluorescence computed tomography (XFCT) when the attenuation maps at the energies of the fluorescence X-rays are unknown. Our previous approach, while yielding good results, was somewhat heuristic and did not necessarily correspond to maximization of a predefined penalized-likelihood objective function. Here we present an iterative algorithm that is guaranteed to increase a predefined objective function at each iteration. The approach alternates between updating the distribution of a given element and updating the attenuation map for that element's fluorescence X-rays. We apply the algorithm to simulated numerical data as well as to real synchrotron data.

In autumn 2005 the GKSS-Research Center Geesthacht in cooperation with Deutsches Elektronen-Synchrotron DESY, Hamburg, started operation of the new synchrotron radiation beamline HARWI-2. The beamline is specialized for materials science experiments using hard X-rays. Recently the fixed-exit monochromator for imaging application was installed. Using different sets of crystals in combination with an adapted setup of the beamline optics allow for using an intense and large monochromatic X-ray beam in the energy range of 15 to 200 keV. Investigations performing microtomography in the different energy regions are presented. Furthermore the user experiment for microtomography operated by the GKSS at beamline BW2 was enhanced to perform continuous tomographic investigations.

A microcomputed tomography (μCT) facility and computational infrastructure developed at the Department of Applied Mathematics at the Australian National University is described. The current experimental facility is capable of acquiring 3D images made up of 2000³ voxels on porous specimens up to 60 mm diameter with resolutions down to 2 μm. This allows the three-dimensional (3D) pore-space of porous specimens to be imaged over several orders of magnitude. The computational infrastructure includes the establishment of optimised and distributed memory parallel algorithms for image reconstruction, novel phase identification, 3D visualisation, structural characterisation and prediction of mechanical and transport properties directly from digitised tomographic images. To date over 300 porous specimens exhibiting a wide variety of microstructure have been imaged and analysed. In this paper, analysis of a small set of porous rock specimens with structure ranging from unconsolidated sands to complex carbonates are illustrated. Computations made directly on the digitised tomographic images have been compared to laboratory measurements. The results are in excellent agreement. Additionally, local flow, diffusive and mechanical properties can be numerically derived from solutions of the relevant physical equations on the complex geometries; an experimentally intractable problem. Structural analysis of data sets includes grain and pore partitioning of the images. Local granular partitioning yields over 70,000 grains from a single image. Conventional grain size, shape and connectivity parameters are derived. The 3D organisation of grains can help in correlating grain size, shape and orientation to resultant physical properties. Pore network models generated from 3D images yield over 100000 pores and 200000 throats; comparing the pore structure for the different specimens illustrates the varied topology and geometry observed in porous rocks. This development foreshadows a new numerical laboratory approach to the study of complex porous materials.

The structure of wood based medium density fiberboard (MDF) has been studied using synchrotron radiation-based x-ray microtomography (SRμCT.) Fully automated 3D segmentation and analysis routines have been developed in order to gain information about individual fibers, the distribution of the fiber material, fiber orientation, fiber surfaces and size and location of contact areas. Representative samples of the analyzed volume data are presented to demonstrate the results of the implemented methods using the VIGRA image processing library.

A dynamic crash loading experiment is performed on a polypropylene foam. Several interrupted shocks are conducted, in between which microtomographic acquisitions are made, showing the evolution of the sample during its compression. This data can help construct and validate predictive models, although, because this material is multiscale (consitutive grains at the mesoscopic scale are made of microscopic closed cells), image processing is required to extract useful quantitative measures. Such processing is described here, so as to determine a representative volume for each grain of the sample, in order to associate to each grain and to each stage of the compression values such as grain density. This can help build a predictive model at the mesoscopic scale.

In studies of inorganic and biogenic structural materials, x-ray absorption microCT (micro Computed Tomography) can be combined to great effect with x-ray scattering. The techniques provide complimentary information, and the limitations of one are offset by the strengths of the other. For example, absorption microCT can supply an accurate, 3D map of the distribution of material within a solid specimen but cannot identify where different crystalline or amorphous phases are to be found (unless compositions or densities differ significantly) or what changes occur in the material itself (amount of plastic deformation, magnitudes of internal stress); this latter information is provided by x-ray scattering (diffraction from crystalline phases and small angle x-ray scattering, SAXS, from nm-sized structures) albeit at much lower spatial resolution. Three examples of studies combining the two approaches are presented: correlation of different scale of crystallographic texture with fatigue crack path and crack closure, studies of damage in monofilament composites and in situ loading of bone.

Optical coupling between the X-ray scintillator and digital camera (typically CCD) is a major design consideration in X-ray microtomography. Previously, we used a pair of 50mm f1.2 lenses, which we determined to be approximately 60 % efficient, that is, the signal to noise ratio is that which would occur if 60 % of the X-ray photons absorbed by the scintillator were directly detected. For larger CCDs, lenses become excessively large, heavy and expensive. For our 60 x 60 mm time-delay integration CCD camera, we used parallel fibre-optic coupling, giving greater efficiency. A problem with this is the scattering of light through the fibre cladding, which reduces image contrast, adding a very blurred image to the sharp image transmitted through the fibres. This problem is ideally suited to solution by deconvolution. Since the high frequency image components are present (direct fibre image) deconvolution can be used to eliminate the low frequency scatter image, without the problems normally associated with de-blurring. The point spread function was assumed to be rotationally symmetrical and was determined from an edge image of a lead plate positioned close to the scintillator. In frequency space, the mid frequency portion was extrapolated into the low frequency portion using a parabolic fit. The difference between the extrapolated and measured low frequency portions was deemed to be the scatter response. This was then added to the frequency response for a perfect delta function to obtain the frequency response used for deconvolution. The results showed excellent correction of the X-ray microtomographic images.

The position of the rotation axis (center of rotation) is an important input parameter for the reconstruction of tomography data. We have recently presented a method for the determination of the center of rotation from sinogram data recorded in parallel-beam tomography, which is based on scoring of reconstructions with image metrics. The influence of noise on the metric value is investigated by simulation using a circular computer phantom. Limits on the precision of the method are discussed by calculation of the metric signal and its noise level. It is shown that for typical count rates and resolutions used in microtomographic imaging, the method enables to determine the center of rotation with a precision of better than 0.06 pixel.

Diffraction enhanced imaging (DEI) is an analyzer-based X-ray phase-contrast imaging method that measures the absorption and refractive properties of an object. A well-known limitation of DEI is that it does not account for ultra-small-angle X-ray scattering (USAXS), which is produced commonly by biological tissue. In this work, an extended DEI (E-DEI) imaging method is described that attempts to circumvent this limitation. The EDEI method concurrently reconstructs three images that depict an object's projected absorption, refraction, and USAXS properties, and can be viewed as an implementation of the multiple-image radiography (MIR) paradigm. Planar and computed tomography (CT) implementations of E-DEI and an existing MIR method are compared by use of computer-simulation studies that employ statistical models to describe USAXS effects.

Microstructural changes like micro deformation and damaging due to tensile load precede the macroscopical failure of a component. In order to contribute to the understanding of such processes, the microstructure of tensile test specimens was imaged by microtomography in the course of deformation. The specimens consist of particle reinforced metal matrix composites (the MMCs Cobalt/Diamond and Al/TiN) manufactured on a powder metallurgical route. Tomograms of a volume in the gauge length of the specimens were reconstructed from the projection data acquired at different deformation stages. Both polychromatic radiation of a microfocus X-ray tube and monochromatic synchrotron radiation were used for projection data acquisition. With the help of 3D data processing 3D surface nets were extracted from the tomograms which indicate the particle/matrix interface. These nets which are composed of triangles were afterwards optimized with respect to the shape of the triangles. Using the triangles as seeds a 3D FE-mesh without gaps consisting of tetrahedra was generated. 3D FE-simulations were carried out utilizing both arbitrary and realistic boundary constraints. Realistic conditions were derived from an iterative matching procedure of tomograms. The effect of finite element type (tetrahedron or hexahedron) on the simulated distribution of stresses was analyzed. The appearance and development of plastic zones in the metal matrix depending on externally applied displacements were studied in the simulations. The calculated peak stresses are compared with the loci of cracks found in the tomograms.

Understanding the distributions of strain within solid bodies undergoing plastic deformations has been of interest for many years in a wide range of disciplines, ranging from basic materials science to biology. However, the desire to investigate these strain fields has been frustrated by the inaccessibility of the interior of most samples to detailed investigation without destroying the sample in the process. To some extent, this has been remedied by the development of advanced surface measurement techniques as well as computer models based on Finite Element methods. Over the last decade, this situation has changed by the introduction of a range of tomographic methods based both on advances in computer technology and in instrumentation, advances which have opened up the interior of optically opaque samples for detailed investigations. We present a general method for assessing the strain in the interior of marker-containing specimens undergoing various types of deformation. The results are compared with Finite Element modelling.

Energy-resolved fan-beam coherent scatter computed tomography (CSCT) is a novel X-ray based tomographic imaging method revealing structural information on the molecular level, namely the momentum-transfer dependence of the coherent scatter cross-section. Since the molecular structure is the source of contrast a very good material discrimination and possibly also medical diagnosis of structural changes of tissue can be achieved with this technique. For the design of a medical or baggage inspection CSCT-scanner acquisition speed is of particular importance. Several performance improvements for CSCT were investigated. The multi-slit fan beam collimator and multi-line scatter detector allow increasing the detected photon flux without compromising angular resolution. Analysis of the noise in reconstructed data leads to the possibility to adjust scan time to the size of the objects to be analyzed. Improved energy resolution of the detector improves momentum-transfer resolution such that angular resolution becomes the limiting factor. Overall, the implemented improvements now enable the real-world application of CSCT.

X-ray computed tomography (XCT) is a powerful nondestructive 3D imaging technique, which enables the visualization of the three dimensional structure of complex, optically opaque samples. High resolution XCT using Fresnel zone plate lenses has been confined in the past to synchrotron radiation centers due to the need for a bright and intense source of x-rays. This confinement severely limits the availability and accessibility of x-ray microscopes and the wide proliferation of this methodology. We are describing a sub-50nm resolution XCT system operating at 8 keV in absorption and Zernike phase contrast mode based on a commercially available laboratory x-ray source. The system utilizes high-efficiency Fresnel zone plates with an outermost zone width of 35 nm and 700 nm structure height resulting in a current spatial resolution better than 50 nm. In addition to the technical description of the system and specifications, we present application examples in the semiconductor field.

X-ray Microtomography bridges the 3D analysis gap between conventional x-ray tomography and TEM tomography. The use of a laboratory-based microfocus source opens up the opportunity to gain additional benefits from in-line phase contrast for enhancing the visibility of fine features, cracks, voids and boundaries in individual views. Coupled with phase retrieval methods, such images can be used as input to conventional reconstruction algorithms for three dimensional visualization. Working at high resolution brings challenges of physical stability of the system. Software approaches to overcoming these difficulties have enabled submicron resolution 3D reconstructions.

X-ray micro-tomography system has been developed at BL47XU in SPring-8. A Fresnel zone plate (FZP) was used as an objective to achieve the 100-nm-order spatial resolution. The system consists of a light source, a Si(111) double crystal monochromator, a beam diffuser made by graphite powder, a condenser zone plate (CZP), high precision stages for sample rotation, FZP objective and an X-ray image detector. The X-ray energy was selected between 7keV and 10keV to obtain fine images for various samples. The FZP and CZP were fabricated by the electron-beam lithography technique. The material of the zone structure is tantalum with thickness of 1μm. The outermost zone width of FZP is 100 nm, and periodic zone width of the CZP is 200 nm (400 nm in pitch). The measured spatial resolution of the optical system was about 160 nm, which had a good agreement with the theoretical value derived from Hopkins' imaging theory. From a tomographic measurement of a concentric resolution test pattern, cross-sectional image with a spatial resolution of better than 300 nm was successfully reconstructed. A small meteorite and some kinds of minerals were successfully observed.

An instrument for high-resolution imaging and tomography has been built at the APS beamline 34 ID-C, Argonne National Laboratory. In-line phase contrast tomography can be performed with micrometer resolution. For imaging and tomography with resolution better than 100nm a hard X-ray microscope has been integrated to the instrument. It works with a Kirkpatrick-Baez (KB) mirror as condenser and a Fresnel-Zone plate (FZP) as an objective lens. 50 nm-features have been resolved in a Nickel structure operating the microscope at a photon energy of 9keV. Phase objects with negligible absorption contrast have been imaged. Tomography scans were performed on photonic crystals.

Hard x-ray full field and scanning microscopy both greatly benefit from recent advances in x-ray optics. In full field microscopy, for instance, rotationally parabolic refractive x-ray lenses can be used as objective lens in a hard x-ray microscope, magnifying an object onto a detector free of distortion. Using beryllium as lens material, a hard x-ray optical resolution of about 100 nm has been obtained in a field of view of more than 500 micrometers. Further improvement of the spatial resolution to below 50 nm is expected. By reconstructing the sample from a series of micrographs recorded from different perspectives, tomographic imaging with a resolution well below one micrometer was achieved. The technique is demonstrated using a microchip as test sample. In scanning microscopy and tomography, the sample is scanned through a hard x-ray microbeam. Different hard x-ray analytical techniques can be exploited as contrast mechanism, such as x-ray fluorescence, absorption, or scattering. In tomographic scanning mode, they yield for example local elemental, chemical, or structural information from inside a specimen. At synchrotron radiation sources, a small and intensive microbeam can be generated by imaging the source onto the sample position in a strongly reducing geometry, e.g., by parabolic refractive x-ray lenses. With nanofocusing refractive x-ray lenses, a lateral beam size of 50 nm was reached. As an example for scanning tomography, we consider tomographic small angle x-ray scattering (SAXS-tomography), reconstructing a series of SAXS patterns related to small volume elements inside a polymer rod made by injection moulding.

Computed angle scan tomography has been implemented for the first time using sample raster scanning in a scanning transmission X-ray microscope. The experimental apparatus, acquisition and data analysis procedures, and first results from fully hydrated river biofilm samples measured from 528-534 eV are reported. The multiple energy images are processed to 3-dimensional quantitative chemical maps of major biological components, such as proteins, polysaccharides and lipids.

It is well known that a rigid in-plane motion can be decomposed into a translation and a rotation around an origin. Based on our previous work [1], we first extend the Helgason-Ludwig consistency condition (HLCC) to cover a general rigid motion in fan-beam geometry. Then, we model the general motion by several parameters, and develop a multi-scale iterative scheme for estimation of the in-plane motion parameters. This scheme determines the motion parameters by numerically minimizing an objective function constructed based on the HLCC. After the motion parameters are estimated, image reconstruction can be performed to compensate for the motion effects. Finally, we implement the algorithm in Matlab and C++, and evaluate its performance in numerical simulations.

This paper investigates the feasibility of reconstructing a Computed Tomography (CT) image from truncated Lambda Tomography (LT), a gradient-like image of it's original. An LT image can be regarded as a convolution of the object image and the point spread function (PSF) of the Calderon operator. The PSF's infinite support provides the LT image infinite support; even the original CT image is of compact support. When the support of a truncated LT image fully covers the compact support of the corresponding CT image, we develop an extrapolation method to recover the CT image more precisely. When the support of the CT image fully covers the support of the truncated LT image, we design a template-based scheme to compensate the cupping effects and reconstruct a satisfactory image. Our algorithms are evaluated in numerical simulations and the results demonstrate the feasibilities of our methods. Our approaches provide a new way to reconstruct high-quality CT images.

In small-animal molecular imaging, bioluminescence tomography (BLT) is used to reconstruct the internal bioluminescent source which can reveal the molecular and cellular information. Based on the general finite element tomographic method, the spatial resolution of source distribution need compromise between a priori fixed discretization degree to the given geometry domain and the computational cost of the reconstruction algorithm. In this contribution, an adaptive finite element methods based tomographic algorithm is represented and used to localize bioluminescent source. In the proposed algorithm, an initial coarse volumetric finite element mesh is provided and a priori knowledge is employed to determine the permissible source region. Furthermore, the local mesh refinement is performed to adaptively reduce the element size of the mesh by virtue of error estimation techniques. The above strategies reduce the ill-posedness of the BLT problem significantly and improve the numerical stability effectively. Numerical simulations with the homogeneous and heterogeneous phantoms, where the synthetic data is obtained through the adaptive finite element solver and Monte Carlo methods, show the effectiveness of the tomographic algorithm.

Breast cancer is the second leading cause of cancer death in women in the United States. Currently, X-ray mammography is the method of choice for screening and diagnosing breast cancer. However, this 2D projective modality is far from perfect; with up to 17% breast cancer going unidentified. Over past several years, there has been an increasing interest in cone-beam CT for breast imaging. However, previous methods utilizing cone-beam CT only produce approximate reconstructions. Following Katsevich's recent work, we propose a new scanning mode and associated exact cone-beam CT method for breast imaging. In our design, cone-beam scans are performed along two tilting arcs for collection of a sufficient amount of data for exact reconstruction. In our Katsevich-type algorithm, conebeam data is filtered in a shift-invariant fashion and then backprojected in 3D for the final reconstruction. This approach has several desirable features. First, it allows data truncation unavoidable in practice. Second, it optimizes image quality for quantitative analysis. Third, it is efficient for sequential/parallel computation. Furthermore, we analyze the reconstruction region and the detection window in detail, which are important for numerical implementation.

Over recent years, various exact cone-beam reconstruction algorithms have been proposed. The derivations of these algorithms are quite complicated, and often difficult to see the fundamental connections among these methods and their key steps. In this paper, we present a straightforward perspective based on the Fourier transform, which is a universal principle for parallel and divergent beam computed tomography (CT). The formulas in this paper are not only consistent with the latest findings in the field but also valid under more general conditions.

The projection equations in the research of discrete tomography are obtained by either counting the number of points that each line passes or computing the fractional areas of the intersection of each strip and the grid. In this work, a system of linear equations for strip-based projections with rational slopes is obtained. The linear dependency number of these equations is derived.

An iterative algorithm is suited to reconstruct CT images from noisy or truncated projection data. However, as a disadvantage, the algorithm requires significant computational time. Although a parallel technique can be used to reduce the computational time, a large amount of communication overhead becomes an obstacle to its performance. To overcome this problem, we proposed an innovative parallel method based on the local iterative CT reconstruction algorithm. The object to be reconstructed is partitioned into a number of sub-regions and assigned to different processing elements (PEs). Within each PE, local iterative reconstruction is performed to recover the sub-region. Several numerical experiments were conducted on a high performance computing cluster. And the FORBILD head phantom was used as benchmark to measure the parallel performance. The experimental results showed that the proposed parallel algorithm significantly reduces the reconstruction time, hence achieving a high speedup and efficiency.

In a previous study, we proposed a helical scanning configuration with triple X-ray sources symmetrically positioned and established its reconstruction algorithm. Although symmetrically positioned sources are convenient in practice, artifacts can be produced in a reconstructed image if the physical sources are not equally spaced. In this work, we develop an exact backprojection filtration (BPF) type algorithm for the configuration with unequally spaced triple sources to reduce the artifacts. Similar to the Tam-Danielsson window, we define the minimum detection window as the region bounded by the most adjacent turns of two helices. The sum of the heights of the three consequent minimum detection windows is equal to that of the traditional Tam-Danielsson window for a single source. Furthermore, we prove that inter-helix PI-lines satisfy the existence and uniqueness properties (i.e., through any point inside the triple helices, there exists one and only one inter-helix PI-line for any pair of helices). The proposed algorithm is of the backprojection-filtration (BPF) type and can be implemented in three steps: 1) differentiation of the cone-beam projection from each source; 2) weighted backprojection of the derivates on the inter-helix PI-arcs; 3) inverse Hilbert transformation along one of the three inter-helix PI-lines. Numerical simulations with 3D Shepp-Logan phantoms are performed to validate the algorithm. We also demonstrate that artifacts are generated when the algorithm for the symmetric configuration is applied to the unequally spaced helices setting.

Multiple source helical cone-beam scanning is a promising technique for dynamic volumetric CT/micro-CT. In the previous studies, we had proposed a helical cone-beam scanning mode with triple x-ray source and detector assemblies that are symmetrically arranged, and proved the property of minimum detection windows under this configuration. Moreover, we had established an exact backprojection filtration (BFP) reconstruction algorithm for this setting. In this paper, we perform simulation studies for this reconstruction algorithm with 3D Shepp-Logan and Defrise phantoms. The implementation of the BFP algorithm in the planar detector geometry consists of three steps. First, the cone-beam projection from each of the three sources is differentiated respectively. Second, the derivates on the three inter-helix PI-arcs are summed up with weights to form the backprojection. Third, inverse Hilbert transformations are performed along each of the three inter-helix PI-lines. The reconstructed images validate the proposed algorithm. Furthermore, this work can be generalized to the case of multiple source helical cone-beam CT.

As a potentially important technology for medical x-ray Computed Tomography (CT), Lambda tomography (LT) is to reconstruct a gradient-like image only from local projection data. Based on our recently derived exact fan-beam LT formula, here we propose a practical cone-beam LT algorithm for LT reconstruction from local data collected along an arbitrary smooth 3D curve. A key step in our algorithm is to determine an appropriate vector perpendicular to the line connecting the x-ray source and an image point. The algorithm is implemented assuming an equi-spatial planar detector and a nonstandard spiral trajectory. The numerical simulation results demonstrate the merits of our method.

In the area of medical XCT reconstruction, simulation projections of mathematical phantoms are extensively adopted by most researchers, based on linear integral calculation. In order to measure realistic projections, energy spectrum of x-ray tube, geometry of phantom and material compositions of all sub-regions should be known. A concise and feasible analytic approach is presented in this paper, herein a modified 3D Shepp Logan phantom is employed as an instance. First, the geometry and linear attenuation coefficients of all ellipses included in a modified 3D Shepp Logan phantom are designed; the intersection points between all ellipses and any special x-ray are computed by solving an equation; the lengths between sequential intersection points and corresponding linear attenuation coefficients are decided by a dedicated algorithm; translating linear attenuation coefficients to CT-numbers; mapping these CT-numbers to the mass densities and mass weights of six standard human being tissues, which are then utilized to acquire an polychromatic cone beam projections. The whole scheme needs lesser storage and computation consumption to reach a higher computation accuracy and precision. To validate feasibility, the simulation projections are post-processed using a Feldkamp reconstruction algorithm, and beam hardening effects are shown clearly.

XCT with polychromatic tube spectrum causes artifact called beam hardening effect. The current correction in CT device is carried by apriori polynomial from water phantom experiment. This paper proposes a new beam hardening correction algorithm that the correction polynomial depends on the relativity of projection data in angles, which obeys Helgasson-Ludwig Consistency (HL Consistency). Firstly, a bi-polynomial is constructed to characterize the beam hardening effect based on the physical model of medical x-ray imaging. In this bi-polynomial, a factor r(γ,β) represents the ratio of the attenuation contributions caused by high density mass (bone, etc.) to low density mass (muscle, vessel, blood, soft tissue, fat, etc.) respectively in the projection angle β and fan angle γ. Secondly, let r(γ,β)=0, the bi-polynomial is degraded as a sole-polynomial. The coefficient of this polynomial can be calculated based on HL Consistency. Then, the primary correction is reached, which is also more efficient in theoretical than the correction method in current CT devices. Thirdly, based on the result of a normal CT reconstruction from the corrected projection data, r(γ,β) can be estimated. Fourthly, the coefficient of bi-polynomial can also be calculated based HL Consistency and the final correction are achieved. Experiments of circular cone beam CT indicate this method an excellent property. Correcting beam hardening effect based on HL Consistency, not only achieving a self-adaptive and more precise correction, but also getting rid of regular inconvenient water phantom experiments, will renovate the correction technique of current CT devices.

An H-L Consistency based beam hardening correction method of CT with polychromatic x-ray tube spectrum has been proposed recently. To identify its effectiveness, a comparison research is completed in the paper between this method and water phantom experiment correction used in current CT devices. For reason of isolating irrelevant influence, the simulated projection data of Forbild head phantom based on physics of medical x-ray imaging are used to evaluate correction effects. Firstly, a virtual circular fan beam CT with known parameters (tube spectrum, added filter, mechanical parameters, etc.) is constructed. Secondly, a simulated isotropic water phantom is used to generate normal correction polynomial in current CT device (called normal correction). Thirdly, for the projection data of given CT phantom, sole-polynomial and bi-polynomial correction based on H-L Consistency, and normal water phantom correction are applied respectively. Fourthly, all the corrected projection data are reconstructed with the same FBP algorithm. The correction effects of beam hardening artifact are compared between those three applied correction methods, especially the differences of correction effects in different slices. Simulation experiments show that the bi-polynomial method can achieve the best effect, although it costs more computation resource, and the H-L Consistency based method exhibit accordant correction effect for different slices, whereas the normal correction cannot adapt all slices equally.

The paper discusses the basic problems and algorithms about cardiac CT reconstructions. A method of selectable rotational velocity is presented for periodic heart rate with circular trajectory. The algorithm can perform any cardiac phase reconstruction exactly or approximately to achieve a desirable temporal resolution. Numerical tests show that the method for selectable rotational velocity is superior to fixed velocity in current cardiac CT.

Tomosynthesis is a technique for reconstructing a 3D object from projection data collected within a limited-angular scanning range. In this paper, we describe and evaluate a methodology for reconstructing a region of interest (ROI) by combining a global low-resolution CT scan and a local high-resolution tomosynthetic scan. First, a low-resolution CT scan is acquired. Then, a high-resolution tomosynthetic scan is performed with respect to the ROI. Finally, the ROI is reconstructed from these two datasets. Our tomosynthetic algorithm is evaluated on a state-of-the-art flat-panel detector based CT system using a standard CT performance phantom. The experimental results demonstrate that our modality fusion approach effectively eliminates the interference from surrounding structures and minimizes the shading problem, as compared to the tomosynthetic results obtained without utilizing the low-resolution CT scan. In conclusion, our approach provides better ROI reconstruction than tomosynthesis, and uses lower dose than CT. Hence, it may be used for temporal bone imaging, etc.

A fiberglass-reinforced polymer blend with a new-generation flame retardant is studied with multi-energy synchrotron X-ray tomography to assess the blend homogeneity. Relative to other composite materials, this sample is difficult to image due to low contrast between fiberglass and the polymer blend. To investigate the chemical composition of this polymer blend, new procedures and algorithms were developed to produce, segment and analyze a chemical concentration distribution that assesses the flame retardant distribution throughout the blend. The results show an extremely homogenous system to the level of the tomography resolution, 3.26 μm. The processes and algorithms used herein include: (a) correction of reconstructed subvolumes absorption values, (b) model for chemical distribution, including the fiberglass matrix, (c) model for chemical distribution, excluding the fiberglass matrix, and (d) an algorithm for generating the radial concentration distribution about the glass fibers in the polymer matrix.

Several methods have been proposed for imaging biological tissue structures at the near micron scale and with user-control of contrast mechanisms that differentiate among the tissue structures. On the one hand, treatment with high-Z contrast agents (Ba, Cs, I, etc.) by injection or soaking and absorption edge imaging distinguishes soft tissue from cornified or bony tissue. This experiment is most compatible with high-bandpass monochromators (ΔE/E between 0.01 - 0.03), such as recently installed at the LSU synchrotron (CAMD). On the other hand, phase contrast imaging does not require any pre-treatment except preservation in formalin, but places more demands upon the X-ray source. This experiment is more compatible with beam lines, such as 13 BM-D at APS, which operates with a narrow bandpass monochromator (ΔE/E ≈ 10^-4). Here, we compare imaging results of soft, cornified and bony tissues across the 2x2 matrix of absorption edge versus phase contrast, and high versus narrow bandpass monochromators. In addition, we comment on new data acquisition strategies adapted to the fragile character of biological tissues: (a) a 100 % humidity chamber, and (b) a data acquisition strategy, based on the Greek golden ratio, that more quickly leads to image convergence. The latter incurs the minor cost of reprogramming, or relabeling, images with order and angle. Subsequently, tomography data sets can be acquired based on synchrotron performance and sample fragility.

This study evaluates laboratory microtomography and microhardness analysis for quantifying the mineral content of bovine enamel. Fifty enamel blocks were submitted individually for 5 days to a pH-cycling model at 37°C and remained in the remineralizing solution for 2 days. The blocks were treated twice daily for 1 min with NaF dentifrices (Placebo, 275, 550, 1,100 μg F/g and Crest^(R)) diluted in deionized water. Surface microhardness changes (%SMH) and mineral loss (ΔZ) were then calculated. Laboratory microtomography was also used to measure total mineral lost (LMM). Pearson's correlation (p<0.05) was used to determine the relationship between different methods of analysis and dose-response between treatments. Dentifrice fluoride concentration and %SMH and ΔZ were correlated (p<0.05). There was a positive relationship (p<0.05) when comparing LMM vs. ΔZ; a negative relationship (p<0.05) was found for %SMH vs. LMM and %SMH vs. ΔZ. Therefore, both mineral quantification techniques provide adequate precision for studying the bovine enamel-pH-cycling demineralization/remineralization model.

Synchrotron microtomography is a tool to quantify the mineralization of dental tissues as well as microhardness analysis, since they provide adequate precision and contrast sensitivity. This study evaluates synchrotron microtomography and microhardness analysis for quantifying the mineral content of bovine enamel. Fifty enamel blocks were submitted individually for 5 days to a pH-cycling model at 37ºC and remained in the remineralizing solution for 2 days. The blocks were treated twice daily for 1 min with NaF dentifrices (Placebo, 275, 550, 1,100 μg F/g and Crest^(R)) diluted in deionized water. Surface microhardness changes (%SMH) and mineral loss (ΔZ) were then calculated. Synchrotron microtomography was also used to measure total mineral lost (SMM). Pearson's correlation (p<0.05) was used to determine the relationship between different methods of analysis and dose-response between treatments. Dentifrice fluoride concentration and %SMH and ΔZ were correlated (p<0.05). There was a positive relationship (p<0.05) when comparing SMM vs. ΔZ; a negative relationship (p<0.05) was found for %SMH vs. SMM and %SMH vs. ΔZ. Based on the results of this study, it was possible to conclude that synchrotron microtomography provides the best spatial resolution and contrast sensitivity for quantifying mineral gradients.

Study of the composition and 3D chemical distribution of the particles that come from space are of great interest since they can provide information about the early stages and evolution of the solar system. The size of these samples varies with the smallest ones in the micron and even sub-micron range. X-ray fluorescence microCT (computed tomography) with focused X-ray beam can be successfully used to study these kinds of samples. This is especially important when sectioning is not feasible, or it is undesirable either due to the risk of contamination, as is the case with comet particles recently collected by the NASA Stardust mission, or the requirement for further analysis by different characterization techniques. X-ray fluorescence microCT measurements on several space samples were performed at the beamline 6-2 using the existing microprobe setup. Two mirror optical system is used for beam focusing with an additional set of KB mirrors located in the hutch near the sample to focus the beam further down to 2x4 microns. Incident X-ray energy is selected with a monochromator in the range of 5 to 20 keV. Fluorescence data was collected with Si(Li) fluorescence detector and PIN diode was used to collect attenuation data that provides additional information for fluorescence tomography reconstruction. The results of the measurements of two micrometeorites with sizes of approximately 100 microns, are presented.

Bioluminescence tomography (BLT) is a new molecular imaging modality, which helps study cancer and other diseases, develop drugs, and so on. This technology localizes and quantifies a bioluminescent source inside a living transgenic mouse, and is very useful in many biomedical applications. In this paper, we propose a novel algorithm based on the radiative transport equation to reconstruct the bioluminescence source distribution from data measured on the external surface of a mouse. Our approach transforms the transport equation into an integral equation of the second kind, and establishes a linear system to link the measured photon fluence rate with the unknown light source variables. A regularization measure is taken to overcome the ill-posedness of the inverse problem. Then, an iterative optimization technique with a simple constrain is employed to compute the desirable solution. The physical phantom experiments have been performed to demonstrate the feasibility of the reconstruction method, and evaluate its performance in terms of source location and power estimation.

We integrated fluorescent X-ray computed tomography (FXCT) and phase-contrast X-ray computed tomography (PCCT), and the feasibility of this fusion imaging was assessed for small animals. Brain tumor model of mouse and cardiomyopathic model of hamsters were examined. The brain and heart were extracted after intravenous injection of cerebral perfusion agent ¹²⁷I-IMP and myocardial fatty acid metabolic agent ¹²⁷I-BMIPP, respectively. Each target organ was fixed by formalin for FXCT and PCCT. Images were obtained three-dimensionally (3D), and the surface contour of brain and heart were determined from 3D-image after re-sampling for the description with the same spatial resolution. These images were fused interactively on displayed images by 3D image manipulation software. In FXCT, cerebral perfusion image with IMP and fatty acid metabolic image with BMIPP were clearly demonstrated at 0.5 mm and 0.2 mm spatial resolution, respectively. PCCT image with 0.03 mm spatial resolution depicted clearly the morphological structures of brain such as cerebral cortex, hippocampus, lateral ventricle and cerebellum, and for heart such as cardiac lumen, papillary muscle, left and right ventricle. On fusion image, localization and degree of abnormality of cerebral perfusion and myocardial fatty acid metabolism were easily recognized. Our results suggested that the integration of FXCT and PCCT is very useful to understand biological state corresponding to its anatomical localization even in small animal.

The intent of this study was to quantify the fracture surface area of dental composites subjected to different aging media. Dental composites, a combination of a resin and glass filler particles, were examined using a high resolution microtomography system developed at beamline 2-BM of the Advanced Photon Source (APS). The composite specimens were 2 mm in diameter and 3 mm in height subjected to a compression load. The initial data set of images was taken with no load, then the load was incrementally increased, a new scan taken, repeatedly, until failure occurred. The images obtained from the tomography scans were reconstructed and analyzed to provide a 3D representation of the crack. This reconstruction involved determining the total solid area, the total area which includes the crack interfaces, and then just the total crack interface area. A ratio was then determined between the control and the loaded specimen. The specimens were aged in various media for 3 months. Preliminary 3D analysis corresponded to previous studies with respect to the aging media and load, i.e., higher loads and aging in ethanol resulted in weaker materials and in this case increased crack areas and compression of the material. When sufficient samples are processed (at present N=6) this 3D analysis will allow statistical comparison of crack area. Supported by NIDCR grant DE07979. Use of the APS was supported by the U.S. DOE, Office of Science, Basic Energy Sciences, under Contract No. W-31-109-ENG-38.