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Journal ArticleDOI

Reconstructing x-ray fluorescence microtomograms

12 Sep 2001-Applied Physics Letters (American Institute of Physics)-Vol. 79, Iss: 12, pp 1912-1914
TL;DR: In this article, a self-consistently estimated attenuation of the fluorescence radiation is used to estimate the attenuation inside the sample, which allows one to reconstruct relative concentrations.
Abstract: X-ray fluorescence microtomography allows one to map element distributions inside a sample with high sensitivity and resolutions in the micrometer range. Quantitative reconstruction of the element concentrations from the fluorescence data requires correction for the attenuation inside the sample. However, the attenuation of the fluorescence radiation is not directly accessible by experiment. The method described self-consistently estimates this attenuation and allows one to reconstruct relative concentrations. This is demonstrated on numerical as well as experimental data. A measure for the quality of the reconstruction is given.
Citations
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Journal ArticleDOI
TL;DR: A three-dimensional variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF), based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector.
Abstract: A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100−350 μm3. Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10−35 μm in the energy range of 3−23 keV and the possibility of performing 3D-XRF analy...

232 citations

Journal ArticleDOI
TL;DR: The potential of coupling pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials is shown, enabling a multimodal analysis of prime importance in materials science, chemistry, geology, environmental science, medical science, palaeontology and cultural heritage.
Abstract: The advent of nanosciences calls for the development of local structural probes, in particular to characterize ill-ordered or heterogeneous materials. Furthermore, because materials properties are often related to their heterogeneity and the hierarchical arrangement of their structure, different structural probes covering a wide range of scales are required. X-ray diffraction is one of the prime structural methods but suffers from a relatively poor detection limit, whereas transmission electron analysis involves destructive sample preparation. Here we show the potential of coupling pencil-beam tomography with X-ray diffraction to examine unidentified phases in nanomaterials and polycrystalline materials. The demonstration is carried out on a high-pressure pellet containing several carbon phases and on a heterogeneous powder containing chalcedony and iron pigments. The present method enables a non-invasive structural refinement with a weight sensitivity of one part per thousand. It enables the extraction of the scattering patterns of amorphous and crystalline compounds with similar atomic densities and compositions. Furthermore, such a diffraction-tomography experiment can be carried out simultaneously with X-ray fluorescence, Compton and absorption tomographies, enabling a multimodal analysis of prime importance in materials science, chemistry, geology, environmental science, medical science, palaeontology and cultural heritage.

188 citations

Journal ArticleDOI
TL;DR: In this paper, an approach to the reconstruction problem is presented, which integrates the information from the three types of signals, i.e., Compton and Rayleigh scattering, for obtaining information on the internal elemental composition of the sample.
Abstract: Conventional x-ray transmission tomography provides the spatial distribution of the absorption coefficient inside a sample. Other tomographic techniques, based on the detection of photons coming from fluorescent emission, Compton and Rayleigh scattering, are used for obtaining information on the internal elemental composition of the sample. However, the reconstruction problem for these techniques is generally much more difficult than that of transmission tomography, mainly due to self-absorption effects in the sample. In this article an approach to the reconstruction problem is presented, which integrates the information from the three types of signals. This method provides the quantitative spatial distribution of all elements that emit detectable fluorescent lines (Z15 in usual experimental conditions), even when the absorption effects are strong, and the spatial distribution of the global density of the lighter elements. The use of this technique is demonstrated on the reconstruction of a grain of the martian meteorite NWA817, mainly composed of low Z elements not measured in fluorescence and for which this method provides a unique insight. The measurement was done at the ID22 beamline of the European Synchrotron Radiation Facility.

149 citations

Journal ArticleDOI
TL;DR: Several modification strategies are suggested, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-topXFCT system for GNP-based preclinical molecular imaging applications.
Abstract: A conventional x-ray fluorescence computed tomography (XFCT) technique requires monochromatic synchrotron x-rays to simultaneously determine the spatial distribution and concentration of various elements such as metals in a sample. However, the synchrotron-based XFCT technique appears to be unsuitable for in vivo imaging under a typical laboratory setting. In this study we demonstrated, for the first time to our knowledge, the possibility of performing XFCT imaging of a small animal-sized object containing gold nanoparticles (GNPs) at relatively low concentrations using polychromatic diagnostic energy range x-rays. Specifically, we created a phantom made of polymethyl methacrylate plastic containing two cylindrical columns filled with saline solution at 1 and 2 wt% GNPs, respectively, mimicking tumors/organs within a small animal. XFCT scanning of the phantom was then performed using microfocus 110 kVp x-ray beam and cadmium telluride (CdTe) x-ray detector under a pencil beam geometry after proper filtering of the x-ray beam and collimation of the detector. The reconstructed images clearly identified the locations of the two GNP-filled columns with different contrast levels directly proportional to gold concentration levels. On the other hand, the current pencil-beam implementation of XFCT is not yet practical for routine in vivo imaging tasks with GNPs, especially in terms of scanning time. Nevertheless, with the use of multiple detectors and a limited number of projections, it may still be used to image some objects smaller than the current phantom size. The current investigation suggests several modification strategies of the current XFCT setup, such as the adoption of the quasi-monochromatic cone/fan x-ray beam and XFCT-specific spatial filters or pinhole detector collimators, in order to establish the ultimate feasibility of a bench-top XFCT system for GNP-based preclinical molecular imaging applications.

148 citations

Journal ArticleDOI
TL;DR: Several complementary approaches to X-ray fluorescence tomography will be routinely available to the biologist in the near future, and these are discussed and applications of biological relevance are reviewed.

143 citations

References
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Journal ArticleDOI
TL;DR: In this article, refractive x-ray lenses with a parabolic profile are described, similar to glass lenses for visible light, which can operate in the range from 2 to 50 degrees of freedom, allowing for magnifications up to 50.
Abstract: We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens.

246 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the absorption density, measured using conventional absorption tomography, to remove absorption effects and compared the resulting corrected reconstructions with the reconstructions degraded by attenuation efforts.
Abstract: The distributions of individual trace elements within a sample can be found using fluorescent computed tomography (FCT). The absorption of incident and fluorescent X-rays results in degraded reconstructions of the distributions. The proposed method uses the absorption density, measured using conventional absorption tomography, to remove absorption effects. A model for FCT with absorption is developed and simulated. The resulting corrected reconstructions are compared to the reconstructions degraded by attenuation efforts. A comparison is made with other methods which utilize knowledge of the sample composition and a standard source to estimate the absorption coefficients used to correct for attenuation effects. >

129 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT) in order to increase measurement sensitivity.
Abstract: This paper describes the possibility of a quantitative calculation of the distribution of a nonradioactive element within a selected cross section with nondestructive methods with the help of X-ray fluorescent tomography (XFCT) In order to increase measurement sensitivity, the use of a lamellar collimator was avoided One of the main problems for the quantitative determination of concentration was absorption of the stimulating synchrotron ray as well as re-absorption of the emitted fluorescent light The absorption coefficients required for a consideration of the absorption processes have been determined with two absorption tomograms The algebraic reconstruction technique (ART) and the maximum likelihood method with expectation maximization (MLEM) were used for the reconstruction of the chemical element to be classified, with close consideration of the absorption phenomenon The experiments were undertaken at the bending-magnet beamline, CEMO, at the laboratory for synchrotron radiation in Hamburg, HASYLAB (45 GeV) (100 mA) The photon intensity flux was approximately 10/sup 9/ photons/mm/sup 2//s The concentration of iodine was calculated with phantoms and an untreated, dissected human thyroid gland with the help of a calibration curve The total error related to the reconstructed mean value amounts to 20% One can find at least an iodide concentration of 06 mmol/l in this experimental setup

99 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used synchrotron-induced x-ray fluorescence (SXRF) in the hard X-ray range to image trace elements in single cells.
Abstract: Imaging of trace elements in single cells was achieved by synchrotron-induced x-ray fluorescence (SXRF) in the hard x-ray range. Monochromatic and “pink” excitations at 14 keV were used with compound refractive lenses resulting in a 1×10 μm2 beam size. The experiment shows that SXRF is well suited for microanalysis of freeze-dried cells, and demonstrated high accuracy in quantitative imaging of trace element in cells treated with pharmacological doses of an iodine-labeled anticancer drug.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a very fast method of computerized critical absorption tomography featuring ∼ 10 μm spatial resolution and high chemical sensitivity is described, which is especially suited to investigating small samples.
Abstract: A very fast method of computerized critical absorption tomography featuring ∼ 10 μm spatial resolution and high chemical sensitivity is described. Synchrotron radiation is used and the method is especially suited to investigating small samples. From a preliminary experiment it is found that layers of neighboring elements only 0.2 μm thick can be distinguished at medium atomic numbers.

55 citations