Lung function has been evaluated in both health and disease states by techniques, such as pulmonary function tests, which generally study aggregate function. These decades old modalities have yielded a valuable understanding of global physiologic and pathophysiologic structure-to-function relationships. However, such approaches have reached their limits. They cannot meet the current and anticipated needs of new surgical and pharmaceutical treatments. 4-D CT can provide insights into regional lung function (ventilation and blood flow) and thus can provide information at an early stage of disease when intervention will have the greatest impact. Lung CT over the last decade has helped with further defining anatomic features in disease, but has lagged behind advances on the cellular and molecular front largely because of the failure to account for functional correlates to structural pathology. Commercially available CT scanners are now capable of volumetric data acquisition in a breath-hold and capable of multi-level slice acquisitions of the heart and lungs with a per slice scan aperture of 50 - 300 msec, allowing for regional blood flow measurements. Static, volumetric imaging of the lung is inadequate in that much of lung pathology is a dynamic phenomenon and, thus, is only detectable if the lung is imaged as air and blood are flowing. This paper review the methodologies and early physiologic findings associated with our measures of lung tissue properties coupled with regional ventilation and perfusion.

Stiffening, or loss of distensibility, of arterial vessel walls is among the manifestations of a number of vascular diseases including pulmonary arterial hypertension. We are attempting to quantify the mechanical properties of vessel walls of the pulmonary arterial tree using parameters derived from high-resolution volumetric x-ray CT images of rat lungs. The pulmonary arterial trees of the excised lungs are filled with a contrast agent. The lungs are imaged with arterial pressures spanning the physiological range. Vessel segment diameters are measured from the inlet to the periphery, and distensibilities calculated from diameters as a function of pressure. The method shows promise as an adjunct to other morphometric techniques such as histology and corrosion casting. It possesses the advantages of being nondestructive, characterizing the vascular structures while the lungs are imaged rapidly and in a near-physiological state, and providing the ability to associate mechanical properties with vessel location in the intact tree hierarchy.

Computerized volumetric warping and registration of 3D lung images can provide objective, accurate, and reproducible measures to the understanding of human lung structure and function. It is also invaluable to the assessment of the presence of diseases and their response to therapy. However, due to the complexity of breathing motion, little work has been carried out in this research area. In this paper, we propose an integrated approach to implement volumetric lung warping and registration from 3D CT images obtained at different stages of breathing. Both feature points and lung surfaces at consecutive frames are incorporated as a priori knowledge for 3D warping to derive an initial sparse comprehensive displacement field. This comprehensive displacement field is then interpolated over the entire volume in an iterative fashion governed by a model derived from continuum mechanics and 3D optical flow. The iteration is based on an objective function defined by a weighted sum of continuity equation, brightness constraint of 3D optical flow and motion-discontinuity-preserving smoothness constraint. Therefore, the 3D warping is accomplished by minimizing such objective function. This integrated scheme is less sensitive to the distribution of feature points and is resilient to the errors introduced in the process of feature point matching. Preliminary results are visualized by overlaying the displacement field with the original images. Effectiveness of the algorithm is also evaluated according to several checking measures. We believe the proposed approach will open up new areas of research in lung image analysis that can make use of the results from lung volumes warping.

The aim of this work was to define reference values for the skeletal and total body volumes (SV and TBV) of human fetuses from 3D reconstructions obtained with spiral computed tomography (CT). The interest of the technique in fetopathy was also estimated. Twenty three fetuses who died just before delivery were studied. The causes of death were not associated with any metabolism abnormality, and all these babies were appropriated for gestational age (GA: 14 - 41.5 wks; Body Weight BW: 22 - 3760 g). They were scanned with a spiral mode on a CT scanner (Elscint CT Twin) using a 2.7 mm slice thickness, a pitch value of 0.7, and a 512 X 512 image matrix. Lengths and volumes were measured on 3D images reconstructed with appropriate windows. High correlations (r greater than 0.95) were found between BW, SV or TBV and the long bone lengths. The ratio SV/TBV was 8.2 plus or minus 0.2%. With the scanning and analysis parameters used, it was extremely difficult to make a precise segmentation of a given organ. However, some few alterations of these parameters could largely increase the potential of the technique in fetopathy.

Two fast, CCD-based three-dimensional CT scanners for in vivo applications have been developed. One is designed for small laboratory animals and has a voxel size of 20 micrometer, while the other, having a voxel size of 80 micrometer, is used for human examinations. Both instruments make use of a novel multiple fan-beam technique: radiation from a line-focus X-ray tube is divided into a stack of fan-beams by a 28 micrometer pitch foil collimator. The resulting wedge-shaped X-ray field is the key to the instrument's high scanning speed and allows to position the sample close to the X-ray source, which makes it possible to build compact CT systems. In contrast to cone- beam scanners, the multiple fan-beam scanner relies on standard fan-beam algorithms, thereby eliminating inaccuracies in the reconstruction process. The projections from one single rotation are acquired within 2 min and are subsequently reconstructed into a 1024 X 1024 X 255 voxel array. Hence a single rotation about the sample delivers a 3D image containing a quarter of a billion voxels. Such volumetric images are 6.6 mm in height and can be stacked on top of each other. An area CCD sensor bonded to a fiber-optic light guide acts as a detector. Since no image intensifier, conventional optics or tapers are used throughout the system, the image is virtually distortion free. The scanner's high scanning speed and high resolution at moderately low radiation dose are the basis for reliable time serial measurements and analyses.

Multiple fan-beam CT combines the advantages of fan-beam and cone-beam CT, i.e. the precise reconstructions of the former and the fast (2D) data acquisition of the latter. Two systems had been realized: a 3D-Micro-CT for the examination of bone samples and small laboratory animals with a spatial resolution of 20 micrometer, and a 3D-pQCT system for the examination of patients with a spatial resolution of 120 micrometer. Both system are able to perform complete 3D examinations within two minutes. In this work we report on pilot studies performed with the 3D-pQCT on the distal radius of patients. First results of longitudinal examinations reveal surprising temporal changes of cortical as well as cancellous bone. Hence it is now possible to base the theoretical models on real data and to consider the consequences of structural changes on the mechanical competence of bone in individual patients.

Micro-computed tomography ((mu) CT) is an emerging technique to nondestructively image and quantify trabecular bone in three dimensions. Where the early implementations of (mu) CT focused more on technical aspects of the systems and required equipment not normally available to the general public, a more recent development emphasized practical aspects of micro- tomographic imaging. That system is based on a compact fan- beam type of tomograph, also referred to as desktop (mu) CT. Desk-top (mu) CT has been used extensively for the investigation of osteoporosis related health problems gaining new insight into the organization of trabecular bone and the influence of osteoporotic bone loss on bone architecture and the competence of bone. Osteoporosis is a condition characterized by excessive bone loss and deterioration in bone architecture. The reduced quality of bone increases the risk of fracture. Current imaging technologies do not allow accurate in vivo measurements of bone structure over several decades or the investigation of the local remodeling stimuli at the tissue level. Therefore, computer simulations and new experimental modeling procedures are necessary for determining the long-term effects of age, menopause, and osteoporosis on bone. Microstructural bone models allow us to study not only the effects of osteoporosis on the skeleton but also to assess and monitor the effectiveness of new treatment regimens. The basis for such approaches are realistic models of bone and a sound understanding of the underlying biological and mechanical processes in bone physiology. In this article, strategies for new approaches to bone modeling and simulation in the study and treatment of osteoporosis and age-related bone loss are presented. The focus is on the bioengineering and imaging aspects of osteoporosis research. With the introduction of desk-top (mu) CT, a new generation of imaging instruments has entered the arena allowing easy and relatively inexpensive access to the three-dimensional microstructure of bone, thereby giving bone researchers a powerful tool for the exploration of age-related bone loss and osteoporosis.

A facility for x-ray computed microtomography (CMT) has been commissioned 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 current apparatus uses a Si (220) channel-cut monochromator covering the energy range from 5 to 35 keV with beam sizes up to 18 mm wide and 4 mm high. The transmitted x-rays are imaged with a single crystal YAG scintillator, a microscope objective and a 1242 X 1152 pixel fast CCD detector. The system spatial resolution is about 3 microns in both the transmission radiographs and the reconstructed slices. Data collection times are approximately 30 minutes. This facility has been used to conduct a number of preliminary studies of earth materials, including inclusion in diamonds, pores in waste repository rocks and fossils. Fluorescence tomography has been conducted on the companion undulator beamline, where we have imaged the internal trace element distribution in interplanetary dust particles.

X-ray microtomography is used to image the internal structure of carbon black filled isobutylene-p-methylstyrene-p- bromomethylstyrene (PIB-PMS/BrPMS or ExxPro^TM) curing bladders before and after use-to-failure in the manufacture of automobile tires. Curing bladders operate under extreme conditions with extended mechanical cycling at high temperatures. Manufacturers typically do not run the bladders until failure but rather a pull policy is established which emphasizes the distribution of cyclic lifetimes. We examine the bladder elastomer structure at a resolution of about 10 microns with the objective of reducing the variability in performance. Using both edge crossing and absorption contrast we identify several types of heterogeneity including voids, foreign inclusions, and the distribution of curative agent from which we infer the uniformity of the cure. The results indicate several potential failure mechanisms. The small number of voids and foreign inclusions are mechanical defects that can initiate cracking. More widespread through the polymer matrix are small regions of polymer devoid of curative agent as shown by absorption edge imaging. These regions may be uncured polymer with poor mechanical and thermal properties that may lead to early failure. After several cure cycles the uncured regions are no longer present in the bladder tread area but they remain near the bead. At high cycles an approximately 500 micrometer thick zinc rich cap develops where the bladder contacts the inner tread area of the tire. This zinc rich cap may cause over-curing of the polymer resulting in crack initiation at the surface of the bladder that contacts the tire.

Synchrotron X-ray microtomography shows vesicular structures for toluene/cement mixtures prepared with 1.22 to 3.58 wt% toluene. Three-dimensional imaging of the cured samples shows spherical vesicles with diameters ranging from 20 to 250 microns; a search with electron microscopy for vesicles in the range of 1 - 20 microns proved negative. However, the total vesicle volume, as computed from the microtomography images, accounts for less than 10% of initial toluene. Evidence for toluene in the cement matrix comes from ²⁹Si MAS NMR spectroscopy, which shows a reduction in chain silicates with added toluene. Also, ²H NMR of d₈-toluene/cement samples shows high mobility for all toluene and thus no toluene/cement binding. A model that accounts for all observations follows: For loadings below about 3 wt%, most toluene is dispersed in the cement matrix, with a small fraction of the initial toluene phase separating from the cement paste and forming vesicular structures that are preserved in the cured cement. Furthermore, at loadings above 3 wt%, the abundance of vesicles formed during toluene/cement paste mixing leads to macroscopic phase separation.

In this study we are interested in microstructure-property relationships in portland cement-based materials. Specifically, we are interested in relating microfracture and damage to bulk mechanical properties. To do this a high resolution three-dimensional scanning technique called x-ray microtomography was applied to measure internal damage and crack growth in small mortar cylinders loaded in uniaxial compression. Synchrotron-based microtomography allows us to resolve internal features that are only a few microns in size. Multiple tomographic scans were made of the same specimen at different levels of deformation, the deformation being applied through a custom built loading frame. Three-dimensional image analysis was used to measure internal crack growth during each deformation increment. Measured load-deformation curves were used to calculate the non-recoverable work of load on the specimen. Incremental non-recoverable work of load was related to measured incremental change in crack surface area to estimate work-of-fracture in three dimensions. Initial results indicate a nearly constant work-of-fracture for the early stages of crack growth. These results show that basic fracture mechanics principles may be applied to concrete in compression, however we must think in terms of 3D multiple crack systems rather than traditional 2D single crack systems.

To understand the effect of pitch on raw data interpolation in multi-slice spiral/helical CT, and provide guidelines for scanner design and protocol optimization. Multi-slice spiral CT is mainly characterized by the three parameters: the number of detector arrays, the detector collimation, and the table increment per X-ray source rotation. The pitch in multi-slice spiral CT is defined as the ratio of the table increment over the detector collimation. In parallel to the current framework for studying longitudinal image resolution, the central fan- beam rays of direct and opposite directions are considered, assuming a narrow cone-beam angle. Generally speaking, sampling in the Radon domain by the direct and opposite central rays is non-uniform along the longitudinal axis. Using a recently developed methodology for quantifying the sensitivity of signal reconstruction from non-uniformly sampled finite points, the effect of pitch on raw data interpolation is analyzed in multi-slice spiral CT. Unlike single-slice spiral CT, in which image quality deceases monotonically as the pitch increases, the sensitivity of raw data interpolation in multi-slice spiral CT increases in an alternating way as the pitch increases, suggesting that image quality does not decrease monotonically in this case. The most favorable pitch can be found from the sensitivity-pitch plot for any given set of multi-slice spiral CT parameters. An example for four-slice spiral CT is provided. The study on the pitch effect using the sensitivity analysis approach reveals the fundamental characteristics of raw data interpolation in multi-slice spiral CT, and gives insights into interaction between pitch and image quality. These results may be valuable for design of multi-slice spiral CT scanners and imaging protocol optimization in clinical applications.

The ID19 3D Synchrotron Radiation Computed MicroTomography (SR (mu) CT) developed at ESRF in Grenoble, uses a 2D detector to record projection images of a sample. If the sample is not completely embedded in the x-ray beam at every angle, the local reconstruction problem may not be solved using the conventional filtered backprojection algorithm. The use of wavelet based algorithms may be a valuable solution for local reconstruction. In this paper, we present a new multiresolution tomographic reconstruction algorithm based on non separable wavelets. The algorithm allows to reconstruct the approximation and detail of an image from its parallel projections. Its application for local tomography is illustrated both from simulated and physical data.

Portable systems for x-ray imaging of objects up to 20-cm in diameter have been developed for field inspection of industrial objects. These systems can be configured with either a linear diode array (45-cm long, 1024-elements, 12- bits/element) or a large-area amorphous-silicon (a-Si) detector (30 X 40-cm², 2304 X 3200-elements, 12- bits/element). Each detector utilizes gadolinium oxysulfide as the scintillation element. X-rays are emitted from an 80 to 300-kVp constant-potential source with a spot size of approximately 1.6-mm. The object can be rotated and the source and detector translated vertically for collection of 'spiral' fanbeam or 'helical' conebeam computed-tomography (CT) data. For low-density objects, the reconstructed spatial resolution of CT data collected with either detector is about the same and the choice of detector is determined by detector parameters such as dynamic range and integration/readout time. For higher-density objects, which need to be imaged at higher energies and for which there is a higher probability of Compton scatter, the linear diode array produces better contrast images of small voids in a scattering medium. A series of experiments designed to test the performance of each detector with and without a scattering medium will be presented.

It is known that the reconstruction produced by the standard cone beam back-projection algorithm, with circular orbit, gives only an approximation to the true three dimensional x- ray attenuation map. It is generally thought that the errors are acceptable if the cone angle is not too large. Such assumptions are based, at least in part, on reconstructions of ellipsoids or spheres. However, this is not representative of most of the specimens used for microtomography which may give rise to larger errors. We have therefore designed a mathematical cone beam phantom generator, capable of calculating a projection data set from analytical specimens described by surface polygons. Using this phantom generator, we have tested a variety of different types of 'specimen' and have shown that when they have certain characteristics, serious errors can occur with very small cone angles, while others will tolerate much larger angles. For a more authentic simulation, a polygon surface was generated from a microtomography scan of a real piece of walrus tusk. This has been used to determine the susceptibility of this type of specimen to cone-beam related errors for various cone angles.

A bench-top x-ray micro-CT scanner was used to evaluate a focusing x-ray optic as a means to augment micro-CT scanner performance. The optic consists of a bundle of hollow glass fibers (25 micrometer diameter) which are arranged and curved so that the optic has an 8 degree input focus and a 4.1 degree output focus cone angle. This optic was placed between our spectroscopy x-ray source (18 keV) and the specimen. The x-ray fluorescent crystal plate was placed as close as possible behind the specimen and the light image generated within it was projected onto a CCD with a lens. The specimen was imaged and rotated about its axis in 1 degree steps until a 360 degree rotation was completed. The resulting, normalized, projection images were submitted to modified Feldkamp cone- beam reconstruction. A 1 cm diameter plastic cylinder, in which glass microspheres (nominally 10, 30, 100 or 300 micrometer diameter) were suspended, was used to compare the spatial resolution of the x-ray optic versus the no-optic scans performed at a range of comparable focal spot-to- specimen distances. The increased flux at the specimen obtained by placing the specimen (and fluorescent crystal) closer to the output focal spot of the optic resulted in increased x-ray flux, thereby reducing scan duration several- fold without increase in penumbral blurring.

Recent development of large area flat panel solid state detector arrays indicates that flat panel image sensors have some common potential advantages: compactness, absence of geometric distortion and veiling glare with the benefits of high resolution, high DQE, high frame rate and high dynamic range, small image lag (less than 1%) and excellent linearity (approximately 1%). The advantages of the new flat-panel detector make it a promising candidate for cone beam volume tomographic angiography imaging. The purpose of this study is to characterize a Selenium thin film transistor (STFT) flat panel detector-based imaging system for cone beam volume tomographic angiography imaging applications. A prototype STFT detector-based cone beam volume tomographic angiography imaging system has been designed and constructed based on the modification of a GE 8800 CT scanner. This system is evaluated using a vascular phantom with different x-ray spectra, different sizes of vessels and different iodine concentration levels. The results indicate that with the currently available STFT flat panel detector, 90 kVp is the optimal kVp to achieve the highest signal-to-noise ratio for volume tomographic angiography imaging and the low contrast resolution of the system is 4 mg/ml iodine for a 2 mm vessel.

Microtomography using synchrotron radiation is widely used in fields of e.g. medicine, biology and material science. Using attenuation contrast at photon energies in the range of 8 to 25 keV and phase contrast at photon energies of 12 keV, 20 keV and 24 keV the method of microtomography is applied to a large number of samples. A comparison of the two different contrast mechanism is presented. Feasibility, advantage and limits of these methods are shown in theory and by experiment. New developments in high-energy microtomography using synchrotron radiation in the energy range of 60 to 100 keV are described. Using attenuation contrast, several samples are investigated. For the investigation of larger specimens with diameters on the order of 1 - 2 cm, the use of a new (mu) CT-technique based on scanning a 2-dim. X-ray detector is demonstrated. At 70 keV photon energy an X-ray LLL-interferometer is tested and used to measure phase projections. For the first time, phase- contrast microtomography could be applied to weakly and normally absorbing material at a high photon energy.

Recent development in phase-contrast X-ray computed tomography using an X-ray interferometer is reported. To observe larger samples than is possible with our previous X-ray interferometer, a large monolithic X-ray interferometer and a separated-type X-ray interferometer were studied. At the present time, 2.5 cm X 1.5 cm interference patterns have been generated with the X-ray interferometers using synchrotron X-rays. The large monolithic X-ray interferometer has produced interference fringes with 80% visibility, and has been used to measure various tissues. To produce images with higher spatial resolution, we fabricated another X-ray interferometer whose wafer was partially thinned by chemical etching. A preliminary test suggested that the spatial resolution has been improved.

Microtomography has successfully been used to characterize loss of structural integrity of wood. Tomographic images were generated with the newly developed third generation x-ray computed microtomography (XCMT) instrument at the X27A beamline at the national Synchrotron Light source (NSLS). The beamline is equipped with high-flux x-ray monochromator based on multilayer optics developed for this application. The sample is mounted on a translation stage with which to center the sample rotation, a rotation stage to perform the rotation during data collection and a motorized goniometer head for small alignment motions. The absorption image is recorded by a single-crystal scintillator, an optical microscope and a cooled CCD array detector. Data reconstruction has provided three-dimensional geometry of the heterogeneous wood matrix in microtomographic images. Wood is a heterogeneous material composed of long lignocellulose vessels. Although wood is a strong natural product, fungi have evolved chemical systems that weaken the strength properties of wood by degrading structural vessels. Tomographic images with a resolution of three microns were obtained nonintrusively to characterize the compromised structural integrity of wood. Computational tools developed by Lindquist et al (1996) applied to characterize the microstructure of the tomographic volumes.

We examine the utility of the lattice Boltzmann method for modeling fluid flow in large microstructures. First, results of permeability calculations are compared to predicted values for several idealized geometries. Large scale simulations of fluid flow through digitized images of Fontainebleau sandstone, generated by X-ray microtomography, were then carried out. Reasonably good agreement was found when compared to experimentally determined values of permeability for similar rocks. We also calculate relative permeability curves as a function of fluid saturation and driving force. The Onsager relation, which equates off-diagonal components of the permeability tensor for two phase flow, is shown not to hold for intermediate to low nonwetting saturation, since the response of the fluid flow to an applied body force was nonlinear. Values of permeability from three phase flows are compared to corresponding two phase values. Performance on several computing platforms is given.

Micro tomography imaging system for rocks and mineral samples was developed at the SPring-8. The experiments were performed on 'in-vacuum type' undulator beam line and bending magnet beam line. Transmission images were measured with an image detector that consists of a fluorescent screen, relay lens, and cooled CCD camera. Convolution back projection method was used to reconstruct tomographic images. As the results of performance test spatial resolution was about 17 micrometer, and the contrast resolution was about 10% in the X-ray linear attenuation coefficient. Three-dimensional structures and textures of some rocks and materials were obtained with the tomography system. Especially the three-dimensional tomographic images of chondrules from Allende meteorite, including a barred olivine chondrule were successfully obtained.

Last year, the X27A beamline at the National Synchrotron Light Source (NSLS) became dedicated solely to X-Ray Computed Microtomography (XCMT). This is a third-generation instrument capable of producing tomographic volumes of 1 - 2 micron resolution over a 2 - 3 mm field of view. Recent enhancements will be discussed. These have focused on two issues: the desire for real-time data acquisition and processing and the need for highly monochromatic beam (.1% energy bandpass). The latter will permit k-edge subtraction studies and will provide improved image contrast from below the Cr (6 keV) up to the Cs (36 keV) k-edge. A range of applications that benefit from these improvements will be discussed as well. These two goals are somewhat counterproductive, however; higher monochromaticity yields a lower flux forcing longer data acquisition times. To balance the two, a more efficient scintillator for X-ray conversion is being developed. Some testing of a prototype scintillator has been performed; preliminary results will be presented here. In the meantime, data reconstruction times have been reduced, and the entire tomographic acquisition, reconstruction and volume rendering process streamlined to make efficient use of synchrotron beam time. A Fast Filtered Back Transform (FFBT) reconstruction program recently developed helped to reduce the time to reconstruct a volume of 150 X 150 X 250 pixels³ (over 5 million voxels) from the raw camera data to 1.5 minutes on a dual R10,000 CPU. With these improvements, one can now obtain a 'quick look' of a small tomographic volume (approximately 10⁶ voxels) in just over 15 minutes from the start of data acquisition.

Artifacts induced by distortions which sometimes occur in two- dimensional projection images can appear in the resulting tomographic reconstructions. We describe a procedure for analyzing, correcting and removing experimental artifacts, and hence reducing reconstruction artifacts. Two-dimensional and three-dimensional images acquired with scanning transmission x-ray microscopy of a sample containing an integrated circuit interconnect show how these procedures can be successfully applied.

Computed tomography for nondestructive evaluation applications has been limited by system cost, resolution, and time requirements for three-dimensional data sets. FlashCT (Flat panel Amorphous Silicon High-Resolution Computed Tomography) is a system developed at Los Alamos National Laboratory to address these three problems. Developed around a flat panel amorphous silicon detector array, FlashCT is suitable for low to medium energy x-ray and neutron computed tomography at 127- micron resolution. Overall system size is small, allowing rapid transportation to a variety of radiographic sources. System control software was developed in LabVIEW for Windows NT to allow multithreading of data acquisition, data correction, and staging motor control. The system control software simplifies data collection and allows fully automated control of the data acquisition process, leading toward remote or unattended operation. The first generation of the FlashCT Data Acquisition System was completed in August 1998, and since that time the system has been tested using x-ray sources ranging in energy from 60 kV to 20MV. The system has also been used to collect data for thermal neutron computed tomography at the Los Alamos Neutron Science Center (LANSCE). System improvements have been proposed to provide faster data collection and greater dynamic range during data collection.

Fluorescent x-ray computed tomography (FXCT) is being developed to detect non-radioactive contrast materials in living specimens. The FXCT system consists of a silicon (111) channel cut monochromator, an x-ray slit and a collimator for fluorescent x ray detection, a scanning table for the target organ and an x-ray detector for fluorescent x-ray and transmission x-ray. To reduce Compton scattering overlapped on the fluorescent K(alpha) line, incident monochromatic x-ray was set at 37 keV. The FXCT clearly imaged a human thyroid gland and iodine content was estimated quantitatively. In a case of hyperthyroidism, the two-dimensional distribution of iodine content was not uniform, and thyroid cancer had a small amount of iodine. FXCT can be used to detect iodine within thyroid gland quantitatively and to delineate its distribution.

The detection of X-ray photons scattered through a sample by the Rayleigh and Compton processes is used to perform tomographic images. A map can thus be obtained, which emphasizes small changes in atomic number Z within the sample. In such a way to distinguish between photons scattered through Rayleigh and Compton processes, a monochromatic photon beam must be used. Choosing a 60 keV photon energy, difference between polyethylene and an aqueous solution containing a low concentration of iodine (0.5 mg.cm^-3) is easily obtained. The most common experimental device involves a collimator with an unique slit. The scanning throughout the slice is performed point by point and the corresponding image can directly be drawn up. Beside the point by point method, the present paper describes a new experimental arrangement and the corresponding reconstruction method. The scanning method is similar to the one used for first generation tomographs. A standard reconstruction algorithm delivers two intermediate images, corresponding to the Compton and Rayleigh contributions. On both images artifacts are present, due to photon attenuation inside the sample. Computation of the ratio between those two images gives a Z map of the sample, free of artifacts. The experiment was performed at the European Synchrotron Radiation Facility (ESRF), in Grenoble (France), on line ID15 B. Due to the very high photon intensity, short measurement times are allowed (around five seconds by point), as well as a good spatial resolution. The voxel size is 1 mm X 1 mm in the plane of the slice, and 0.3 mm in the third direction.

The coherence of third generation synchrotron beams makes a trivial form of phase-contrast radiography possible. It is based on simple propagation and corresponds to the defocusing technique of electron microscopy. Most of the work until now uses this technique to detect phase discontinuities associated with edges in the specimen. The tomographic reconstruction was initially performed using the algorithm for X-ray absorption tomography, a temporary and obviously unsatisfactory approach. This results in a decent solution for some cases, but gives rise to artifacts and does not reveal quantitatively the inner structure of the object. However the Fresnel diffraction fringes contain in an entangled form the phase modulation by the sample. We have successfully implemented a method for quantitative phase tomography based on the propagation technique. The reconstruction of the 3D refractive index distribution involves two steps. First the phase modulation is numerically retrieved from the combination of several images recorded at different distances. This holographic reconstruction process is repeated for a large number of angular positions of the specimen. Then the conventional filtered backprojection algorithm is used to determine the three dimensional distribution from the retrieved phase maps. The reconstructed 3D image of a complicated polystyrene foam sample has a straightforward interpretation with a spatial resolution limited by the detector to 1 - 2 microns.

Various apparatus for x and (gamma) -ray computed tomography (CT) have been constructed by us during the last 20 years, with the aim of producing simple and low-cost systems for nondestructive testing. The first one was constructed in 1980 and used an Am²⁴¹ radioactive source emitting 59.6 keV (gamma) -rays and a single NaI(Tl)-x ray detector. Successively, the radioactive source was substituted during the years by x-ray tubes, and the single detector by multi- detection system such as arrays of detectors and image intensifiers. The last CT-scanner employs a 160 kV x-ray tube and a 6' X 6' image intensifier coupled through a lens to a cooled CCD-camera. At the same time, also (gamma) CT-scanners were constructed for large size and/or high-density samples. These are based on Ir¹⁹² or Cs¹³⁷ radioactive sources coupled to a single NaI(Tl)(gamma) -ray detector. The characteristics and properties of the CT-scanners based on the use of x-ray tubes, emitting x-rays in the energy range 20 - 100 keV, and on (gamma) emitting radioisotopes (Ir¹⁹² and Cs¹³⁷) have been studied and will be described in this paper. Various types of objects have been studied: test objects and common objects such as tree trunks, wood fragments, nuts, ceramic samples, insulators and, etc. Samples have been imaged, after using iodine compounds as tracers.

First experimental results of fluorescence microtomography with 6 micrometer resolution obtained at the ESRF are described. The set-up comprises high quality optics (monochromator, mirrors, focusing lenses) coupled to the high energy/brilliance/coherence of the ID 22 undulator beamline. The tomographic set-up allows precise measurements in the 'pencil-beam' geometry. The image reconstruction is based either on the filtered back-projection (FBT) method or on a modification of the algebraic reconstruction method (ART) but includes simplifications of the model. The quality and precision of the 2D reconstructed elemental images of two phantom sample are encouraging. The method will be further refined and applied for the analysis of more complex inhomogeneous samples.

At the ESRF micro-fluorescence, imaging and diffraction ((mu) - FID) beamline ID 22, a microtomography setup has been operational for several months. The coherence properties of the high-energy (10 to 70 keV) X-ray undulator beam at ID 22 make the setup especially suited for phase-contrast tomography including possible holographic reconstruction, but it has also provided to be well adapted to absorption tomography. A fast- readout, low-noise CCD camera makes time-resolved imaging possible. Recent developments in magnifying X-ray optics such as Compound Refractive Lenses (CRL) and Fresnel Zone Plates (FZP) open up the field of magnified-X-ray imaging with a resolution of less than 300 nm. Imaging techniques using a 'pink beam,' i.e. a beam with limited monochromaticity obtained by filtering one harmonic from the undulator spectrum, can increase flux in intensity-limited experiments.

The combination of high-brilliance x-ray sources, fast detector systems, wide-bandwidth networks, and parallel computers can substantially reduce the time required to acquire, reconstruct, and visualize high-resolution three- dimensional tomographic data sets. A quasi-realtime computed x-ray microtomography system has been implemented at the 2-BM beamline at the Advanced Photon Source at Argonne National Laboratory. With this system, a complete tomographic data set can be collected in about 15 minutes. Immediately after each projection is obtained, it is rapidly transferred to the Mathematics and Computing Sciences Division where preprocessing and reconstruction calculations are performed concurrently with the data acquisition by a SGI parallel computer. The reconstruction results, once completed, are transferred to a visualization computer that performs the volume rendering calculations. Rendered images of the reconstructed data are available for viewing back at the beamline experiment station minutes after the data acquisition was complete. The fully pipelined data acquisition and reconstruction system also gives us the option to acquire the tomographic data set in several cycles, initially with coarse then with fine angular steps. At present the projections are acquired with a straight-ray projection imaging scheme using 5 - 20 keV hard x rays in either phase or amplitude contrast mode at a 1 - 10 micrometer resolution. In the future, we expect to increase the resolution of the projections to below 100 nm by using a focused x-ray beam at the 2-ID-B beamline and to reduce the combined acquisition and computation time to the 1 min scale with improvements in the detectors, network links, software pipeline, and computation algorithms.

Experimental data and results from a detailed Monte Carlo (MC) simulation of X-ray Fluorescence, Compton and Rayleigh scattering tomography are presented. The MC model was developed by the authors for aiding the optimization and evaluation of synchrotron radiation induced X-ray fluorescence (SRXRF) experiments. The code simulates complete X-ray fluorescence spectra in the incident energy range of 1 - 100 keV, including K,L fluorescent lines and Compton, Rayleigh scattering contributions. This generalized simulation model describes the interactions between X-ray photons and heterogenous samples. The MC code was evaluated by comparisons of simulated and experimental X-ray fluorescent and scattering tomography data. These data were collected at HASYLAB, beamline L (polychromatic setup) and BW5 (monochromatic setup). Good agreement was found between experimental and simulated results.