The fundamental issue of reconstructing a porous medium is examined anew in this paper, thanks to a sample of low-porosity Fontainebleau sandstone that has been analyzed by computed microtomography. Various geometric properties are determined on the experimental sample. A statistical property, namely, the probability density of the covering radius, is determined. This is used in order to reconstruct a porous medium by means of a Poissonian generation of polydisperse spheres. In a second part, the properties of the real experimental sample and of the reconstructed one are compared. The most important success of the present reconstruction technique is the fact that the numerical sample percolates despite its low porosity. Moreover, other geometrical features and conductivity are found to be in good agreement.

The application of synchrotron radiation in medical research has become a mature field of research at synchrotron facilities worldwide. In the relatively short time that synchrotrons have been available to the scientific community, their characteristic beams of UV and X-ray radiation have been applied to virtually all areas of medical science which use ionizing radiation. The ability to tune intense monochromatic beams over wide energy ranges differentiates these sources from standard clinical and research tools. At the European Synchrotron Radiation Facility (Grenoble, France), a major research facility is operational on an advanced wiggler radiation beamport, ID17. The beamport is designed to carry out a broad range of research ranging from cell radiation biology to in vivo human studies. Medical imaging programs at ID17 include transvenous coronary angiography, computed tomography, mammography and bronchography. In addition, a major research program on microbeam radiation therapy is progressing. This paper will present a very brief overview of the beamline and the imaging and therapy programs.

A fixed-exit monochromator has been constructed for computed tomography (CT) studies at the Medical Beamline of the European Synchrotron Radiation Facility. A non-dispersive pair of bent Laue-type crystals is used, and the first crystal is water-cooled. The monochromator operates at energies from 18 to 90 keV, and the maximum width of the beam is 150 mm. The performance of the monochromator is studied with respect to the beam intensity and energy distributions, and a close agreement is found between the calculated and experimental results. The intensity is between 10(9) and 10(10) photons s(-1) mm(-2) under typical operating conditions. The harmonic content of a 25 keV beam is about 30% at the minimum wiggler gap of 25 mm (field 1.57 T) and decreases by an order of magnitude when the gap is increased to 60 mm (field 0.62 T). The experimental set-up for CT studies includes dose monitors, goniometers and translation stages for positioning and scanning the object, and a 432-element linear-array Ge detector. Examples from phantom studies and in vivo animal experiments are shown to illustrate the spatial resolution and contrast of the reconstructed images.

PURPOSE To examine tissue lesions caused by microplanar beams of synchrotron-generated X-rays in Drosophila melanogaster using stereomicroscopy, light and electron microscopy. MATERIALS AND METHODS Pupae were irradiated by 25-microm wide, 1.175 mm-high parallel microplanes at 100 microm on-centre intervals, at 20, 24, 32, 36, 48 or 72 h of development, with absorbed doses per microplane between 75 and 3,000 Gy. RESULTS Transverse or longitudinal irradiation with in-slice absorbed doses of 75 or 375 Gy caused no recognizable effects. All pupae irradiated at or after 48 h developed normally. Conversely, the development to adulthood was delayed in 90% of pupae irradiated at 24h with doses of 750 Gy. However, neither those pupae nor adults that hatched after pupal irradiation at 48 and 72 h displayed morphological changes. Pupae exposed at 48 h of development to 3,000 Gy developed into adults with sharply delimited lesions in the irradiated microplanes of the compound eye or the cuticle of wings and abdomen. CONCLUSIONS Post-mitotic eukaryotic cells can survive radiation doses of 3,000 Gy largely undamaged, even at the beginning of the terminal morphogenesis. The extremely sharp delimitation between damaged tissue microplanes and adjacent intact tissues may be relevant for future perspectives of radiosurgery.

At the European Synchrotron Radiation Facility (ESRF) a beamport has been instrumented for medical research programs. Two facilities have been constructed for alternative operation. The first one is devoted to medical imaging and is focused on intravenous coronary angiography and computed tomography (CT). The second facility is dedicated to pre-clinical microbeam radiotherapy (MRT). This paper describes the instrumentation for the imaging facility. Two monochromators have been designed, both are based on bent silicon crystals in the Laue geometry. A versatile scanning device has been built for pre-alignment and scanning of the patient through the X-ray beam in radiography or CT modes. An intrinsic germanium detector is used together with large dynamic range electronics (16 bits) to acquire the data. The beamline is now at the end of its commissioning phase; intravenous coronary angiography is intended to start in 1999 with patients and the CT pre-clinical program is underway on small animals. The first in vivo images obtained on animals in angiography and CT modes are presented to illustrate the performances of these devices.

X-ray computed microtomography is particularly well suited for studying trabecular bone architecture, which requires three-dimensional (3-D) images with high spatial resolution. For this purpose, we describe a three-dimensional computed microtomography (microCT) system using synchrotron radiation, developed at ESRF. Since synchrotron radiation provides a monochromatic and high photon flux x-ray beam, it allows high resolution and a high signal-to-noise ratio imaging. The principle of the system is based on truly three-dimensional parallel tomographic acquisition. It uses a two-dimensional (2-D) CCD-based detector to record 2-D radiographs of the transmitted beam through the sample under different angles of view. The 3-D tomographic reconstruction, performed by an exact 3-D filtered backprojection algorithm, yields 3-D images with cubic voxels. The spatial resolution of the detector was experimentally measured. For the application to bone investigation, the voxel size was set to 6.65 microm, and the experimental spatial resolution was found to be 11 microm. The reconstructed linear attenuation coefficient was calibrated from hydroxyapatite phantoms. Image processing tools are being developed to extract structural parameters quantifying trabecular bone architecture from the 3-D microCT images. First results on human trabecular bone samples are presented.

Holography with high energy x-rays is now feasible due to the coherence properties of third generation synchrotron sources. Simple in-line holographic techniques can be used to generate edge-enhanced images which for many samples can be interpreted without direct phase retrieval. The coherence properties of such sources and their exploitation for phase-contrast microimaging are demonstrated. The technique can easily be combined with computed microtomography (CMT) data collection and reconstruction strategies for three-dimensional imaging. A dramatically improved image contrast, as compared with absorption CMT, was obtained when imaging a wet human coronary artery specimen. In the tomograms, previously invisible detail could be visualized with absorbed doses below the level where radiation damage impedes the imaging. The results indicate the considerable potential of the in-line holographic CMT method in three-dimensional biomedical microscopy.

Recently developed high resolution computed microtomography (CMT) using synchrotron X-ray sources is analogous to conventional medical CT scanning and provides the ability to obtain three-dimensional images of specimens with a spatial resolution on the order of micrometers. Application of this technique to the study of core samples has previously been shown to provide excellent two- and three- dimensional high resolution descriptions of pore structure and mineral distributions of core material. Recently, computed microtomographic endpoint saturation images of a fluid filled sandstone core sample were obtained using a microtomographic apparatus and a high energy X-ray beam produced by a superconducting wiggler at the National Synchrotron Light Source at Brookhaven National Laboratory. Images of a 6 mm subsection of the one inch diameter core sample were obtained prior and subsequent to flooding to residual oil. Both oil and brine phases were observable within the imaged rock matrix. The rock matrix image data was used as input to a fluid transport simulator and the results compared with the end point saturation images and data. These high resolution images of the fluid filled pore space have not been previously available to researchers and will provide valuable insight to fluid flow, and provide data as input into and validation of high resolution porous media flow simulators, such as percolation-network and lattice Boltzmann models.

A monochromatic computed tomography (CT) system for clinical studies in brain pathology is part of the medical beamline ID 17 at the ESRF (European Synchrotron Radiation Facility). We have carried out preliminary phantom studies to determine the minimum detectable iodine and gadolinium concentrations by the K-edge subtraction technique as well as the minimum detectable change in potassium concentration by dual-energy quantitative CT.

M.E. Coles, SPE, R.D. Hazlett, and E.L. Muegge, Mobil E& P Technical Center, K.W. Jones, B. Andrews, B. Dowd, P. Siddons, and A. Peskin, Brookhaven National Laboratory, P. Spanne, European Synchrotron Facility, W.E. Soll, Los Alamos National LaboratoryAbstract. High resolution computed microtomography (CMT) using synchrotron X-ray sources provides the ability to obtain three-dimensional images of specimens with a spatial resolution on the order of micrometers. Microimaging capabilities at Brookhaven National Laboratory's National Synchrotron Light Source have been enhanced to provide larger and higher resolution 3-D renderings of pore networks in reservoir rocks at a fraction of the time required in previous first generation scanning methods. Such data are used to model single and multiphase flow properties in digital images of real porous media. Pore networks are analyzed for tortuosity and connectivity measures, which have been elusive parameters in transport property models. We present examples of porosimetry simulation via network modeling to produce initial water saturation and residual oil distributions in a water-wet pore system. Furthermore, pore networks can provide the boundary condition framework for more rigorous simulations of displacement, such as in the lattice Boltzmann simulated waterflood example provided. Direct comparison between simulation and experiment is also possible. CMT images of a 6 mm subsection of a one inch diameter reservoir core sample were obtained prior and subsequent to flooding to residual oil. The fluid distributions from CMT, lattice Boltzmann waterflood simulation, and percolation-based network modeling were found to be highly correlated. Advances in 3-D visualization, implemented in Brookhaven National Laboratory's 3-D theater, will allow even greater digestion and interpretation of phenomena dependent upon pore interconnectivity and multipore interactions.Introduction. Computed Microtomography (CMT) has been available at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory for many years. First generation scanning methods gave high resolution images of geological and biological samples approaching 1 m resolution. First generation scanning provided necessary detail in moderate to high permeability porous media samples for transport property modeling with computational fluid dynamics methods. The time requirements of first generation methods limited the number of samples which could be investigated and restricted the potential of in-situ experimental monitoring. Implementation of array detection technology enables acquisition of larger 3-D volumes at a fraction of the time required in first generation scanning. Initial implementation, however, was limited by the resolution of fluorescing elements of the detector material, on the order of 10 m rather than 1 m. With the introduction of expansion optics, images of 2.7 m resolution have been obtained containing in the neighborhood of 3x 107 voxels. Improvements in data acquisition, transmission, and reconstruction have reduced the time requirements to produce such a volume to a few hours. Herein we document the status of CMT at the NSLS and display a variety of applications using both first generation and state-of-the-art image data on reservoir rock samples.Advances in Imaging. A schematic of the CMT apparatus is provided as Figure 1, X-ray CMT produces a cross-sectional map, or slice, of linear x-ray attenuation coefficients inside a small sample. To obtain the data for a reconstructed slice, the x-rays transmitted through a single slice of the sample are recorded on a linear array of detectors. The sample is rotated, with the axis of rotation perpendicular to the plane of the incident beam, by a discrete angular interval determined by the linear resolution desired. The transmission of each ray through the sample, along a line from the source to the detector is recorded; this represents a line integral of the attenuation coefficients along this ray. The procedure is repeated for each angular view until the sample has been rotated by 180 in the x-ray beam. P. 413

Microimaging techniques with synchrotron radiation demand fast, on-line x-ray detectors with a spatial resolution in the micrometer or submicrometer range. For this task an x-ray detector based on a transparent, i.e., nonscattering, luminescent screen has been developed. Its performance is described experimentally and theoretically. The detector consists of an Y3Al5O12:Ce screen, microscope optics, and a low-noise CCD camera, operated at x-ray energies between 10 and 50 keV. Good image quality is achieved if the depth of focus of the optical system is matched to the x-ray absorption length or thickness of the scintillator. A spatial resolution of 0.8 µm fwhm (1000 line pairs/mm with 10% contrast) was measured by recording the interferogram of a boron fiber. First applications in phase contrast imaging and microtomography are shown.

A feasibility study of soft-tissue imaging based on x-ray wide-angle diffraction contrast has been performed at the medical beamline of the European Synchrotron Radiation Facility (ESRF). The technique employs computed-tomography algorithms to reconstruct from one data set the spatial distribution of several tissues differentiated by their diffraction properties. Radial diffraction profiles are measured in parallel projections from the sample and decomposed into material-selective weighting factors, which form the sinograms for the reconstructions. Attenuation effects-inherent in imaging techniques using scattered radiation-are efficiently corrected for by a ray-tracing method applied to the corresponding absorption image.Images of 7 cm diameter samples composed of fat, bone and muscle were generated at 60 and 80 keV x-ray energy. The highest surface-absorbed dose was 24 mGy, but substantial contrast could still be obtained at 7 mGy, indicating potential applicability in medical imaging. The dominant noise contribution in the images stems from the detection system, pointing to a possible decrease in the surface-absorbed dose for an optimized system of more than a factor of 2.

Results obtained on the ID19 beamline at ESRF, where particularly high coherence is associated with the long source-to-sample distance (145 m) and the small size of the X-ray source (approximate to 0.1 mm), illustrate the possibilities of imaging using coherence. These features make the imaging of phase objects extremely simple, since a 'propagation' technique, similar to the defocusing mode of electron microscopy and to in-line Gabor holography in optics, can be used. The physical principle involved is Fresnel diffraction.We used this 'propagation' technique both to measure, via the figures obtained from a fiber and a periodic grating, the source size, and to image objects with negligible absorption for hard X-rays but appreciable variations in optical path length. Examples of the latter are two or three-dimensional (tomographic) images of light natural or artificial materials (polymers, wood, crystals, alloys, composites or ceramics with inclusions, holes, cracks,...). The three-dimensional reconstruction can be performed either with a filtered back-projection algorithm designed for attenuation tomography, which was shown to be a good approximation in some cases, or with a phase reconstruction procedure similar to that used for electron microscopy. The spurious images associated with beamline components, and the conditions for coherence preservation are also briefly discussed.

A system of truly 3D microtomography using the coherent synchrotron radiation delivered by ESRF, has been developed. We discuss the specificities of such a system relatively to the coherence property. Indeed, this property is responsible, in addition to the conventional effects of attenuation, of phase contrast phenomena occuring when the sample is at a non zero distance from the detector. These are related to the interference between the waves diffracted by the sample after propagation. We show that under some conditions, it is possible to use the conventional reconstruction algorithms. In this case, the reconstructed image is the sum of the absorption image, and a derivative of the real part of the complex refractive index.

Cross-sectional information on low electron density materials can be obtained by probing a sample with a 60 keV coherent synchrotron x-ray beam in an in-line holography setup. Such objects are practically transparent to high energy x rays and create a phase shift of the wave front only. Images of a 100 μm diameter boron fiber were recorded in the extreme near field region, where contrast occurs only at interfaces between regions with different decrements of refractive index. Theoretical simulations are in good agreement with the measured intensities. In a tomographic reconstruction the 15 μm diameter core of the fiber is clearly visible, demonstrating the possibility of reconstructing three dimensional interfaces between low density materials.

The mechanical properties of bone are directly linked to its trabecular structure. A computed microtomography (CMT) system allowing high resolution three-dimensional imaging of bone samples is reported. The CMT technique benefits from the outstanding properties of synchrotron radiation (i.e. energy tunability, monochromaticity, high photon flux). The detector is based on a two-dimensional digital CCD camera coupled to a fluorescent screen through light optics. A spatial resolution of 9 micrometers (55 line pairs/mm) at 10% contrast was obtained. CMT, which is a non-destructive imaging technique, seems promising for the investigation of bone trabecular structure.

X-ray tomography is often utilized to evaluate and characterize structural characteristics within reservoir core material systems. Generally, medical computed tomography (CT) scanners have been employed because of their availability and ease of use. Current spatial resolutions of conventional medical CT scanners have, however, not allowed their use in obtaining pore level characterizations for most core samples. Recently developed high resolution computed microtomography (CMT) using synchrotron radiation x-ray sources is analogous to conventional medical CT scanning and provides the ability to obtain three dimensional characterization of specimens with a spatial resolution on the order of microns. Application of this technique to the study of core samples provides excellent two and three dimensional high resolution description of pore structure and mineral distributions. Statistical and variogram analysis of the microtomographic images provide descriptors characteristic of the specific core material. Pore space interconnectivity is accurately characterized and visualized. Pore level endpoint saturation microtomograms obtained during a core flood of a sandstone sample are presented.

The possibilities to determine the internal structure of low density materials by a simple microtomography setup with high energy synchrotron x-rays are demonstrated experimentally. The coherent properties of a 50 keV x-ray beam at the ESRF wiggler beamline are used to observe phase-contrast images of a boron fiber, which has negligible absorption in this energy range. Images of the boron fiber are recorded with a high-resolution x-ray film at various distances up to 2 m. For microtomography studies, 61 images are taken over an angular range of 180 degrees. In the reconstructed cross sections, the hollow, 15-mm-diameter core of the fiber is clearly visible.