Synchrotron Radiation Micro-CT Imaging of Bone Tissue

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A comprehensive study of the use of temporal moments in time-resolved diffuse optical tomography: part II. Three-dimensional reconstructions

International audienceThis paper addresses the inverse problem of time-resolved (fluorescence) diffuse optical tomography from temporal moments of the measurements. A methodology that enables one to provide fairly comparable reconstructions is presented. The proposed reconstruction methodology is applied to infinite medium synthetic phantoms in the transmission geometry. Reconstructions are performed for moment orders increasing from 0 to 3. The reconstruction quality is shown to be increasing when higher moment orders are added. However, the value of the highest useful moments order strongly depends on the number of photons that can be acquired. In particular, it can be considered that the benefit of using higher order moments vanishes when fewer than 108 photons are detected. The evolution of the reconstruction quality with respect to the optical properties of the medium and fluorescence lifetime is also shown

An explicit closed-form solution to the limited-angle discrete tomography problem for finite-support objects

An explicit formula is presented for reconstructing a finite-support object defined on a lattice of points and taking on integer values from a finite number of its discrete projections over a limited range of angles. Extensive use is made of the discrete Fourier transform in doing so. The approach in this article computes the object sample values directly as a linear combination of the projections sample values. The well-known ill-posedness of the limited angle tomography problem manifests itself in some very large coefficients in these linear combinations; these coefficients (which are computed off-line) provide a direct sensitivity measure of the reconstruction samples to the projections samples. The discrete nature of the problem implies that the projections must also take on integer values; this means noise can be rejected. This makes the formula practical. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 174–180, 1998Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35065/1/14_ftp.pd

Registration of phase contrast images in propagation-based X-ray phase tomography

International audienceX-ray phase tomography aims at reconstructing the 3D electron density distribution of an object. It offers enhanced sensitivity compared to attenuation-based X-ray absorption tomography. In propagation-based methods, phase contrast is achieved by letting the beam propagate after interaction with the object. The phase shift is then retrieved at each projection angle, and subsequently used in tomographic reconstruction to obtain the refractive index decrement distribution, which is proportional to the electron density. Accurate phase retrieval is achieved by combining images at different propagation distances. For reconstructions of good quality, the phase-contrast images recorded at different distances need to be accurately aligned. In this work, we characterise the artefacts related to misalignment of the phase-contrast images, and investigate the use of different registration algorithms for aligning in-line phase-contrast images. The characterisation of artefacts is done by a simulation study and comparison with experimental data. Loss in resolution due to vibrations is found to be comparable to attenuation-based computed tomography. Further, it is shown that registration of phase-contrast images is nontrivial due to the difference in contrast between the different images, and the often periodical artefacts present in the phase-contrast images if multilayer X-ray optics are used. To address this, we compared two registration algorithms for aligning phase-contrast images acquired by magnified X-ray nanotomography: one based on cross-correlation and one based on mutual information. We found that the mutual information-based registration algorithm was more robust than a correlation-based method

Nonlinear ultrasound monitoring of fatigue microdamage accumulation in cortical bone

Accumulation of bone micro-damage is suspected to lead to severe impairment of mechanical properties with an increase in skeletal fragility and fracture risk. The objective of the study was to evaluate the potential of Nonlinear Resonant Ultrasound Spectroscopy (NRUS) for measuring micro-damage accumulation in cortical bone using four-point bending cycling fatigue. Sixteen human cortical bone specimens were machined as parallelepiped beams. Damage progression was controlled by measuring the linear elastic beam theory modulus (E LEBT ), known to reflect microdamage accumulation. Before and between each damage step, the nonlinear ultrasonic elastic coefficient was measured by NRUS. At the end of each cycling fatigue, a subset of bone samples was measured by μCT at the European Synchrotron Radiation Facility. Results showing a progressive increase of nonlinear ultrasonic elastic coefficient along fatigue cycling suggest that NRUS measurements are sensitive to micro-damage accumulation. The results mentioned above were validated using synchrotron radiation μCT. The variation of elastic nonlinearity was found to be significantly correlated to the variation of number density of small microcracks which almost doubled in damaged regionsThis research was supported by the Agence Nationale pour la Recherche (ANR), France (Grant BONUS_07BLAN0197

Bone microarchitecture in human fetuses

Bone microarchitecture is receiving increasing attention in the assessment of the biomechanical properties of bone. While it is well characterized in normal and pathologic human subjects, few quantitative data are available in human fetal development. In this paper, quantitative parameters of bone microarchitecture in developing human bone are reviewed from the literature and supplemented by new data from the femoral metaphysis of human fetuses. The samples were imaged using synchrotron radiation 3D micro-CT and processed using customized analysis methods. This technique provides 3D model independent morphometric parameters, anisotropy, connectivity and geometry characteristics, as well as information on mineralization. The morphometric parameters obtained on fetal vertebrae and femurs evidenced a dense trabecular structure as compared to that of young adults. The histomorphometric and the 3D micro- CT analysis were consistent to show a significant increase of trabecular bone volume with gestational age. Trabecular bone was found isotropic in vertebral bodies and anisotropic in femoral metaphysis, demonstrating a radial growth in vertebrae, and a longitudinal spreading out in long bones such as the femurs. Trabecular thickness in the mature bone of vertebral body and femoral metaphysis was around 100 μm, which was in agreement with histomorphometric evaluation. In the femoral metaphysis, three-dimensional analysis confirmed the thickening of trabeculae with the distance to the growth plate, and an estimated rate of thickening around 3 μm/day previously obtained in histomorphometry. The 3D network was highly connected, and our new geometrical analysis technique showed a strong prevalence of rod structure as compared to the plate structure in cancellous bon

Segmentation and characterization of 3D micro-CT images: application to bone tissue

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Tomographie X 3D à différents contrastes pour l’étude des matériaux biologiques à haute résolution

International audienceL'introduction de la tomographie par rayons X dans le domaine médical dans les années 1970 a été une avancée majeure puisqu'il s'agissait de la première technique permettant d’imager des coupes de l’anatomie humaine de façon non destructive. Aujourd'hui, la tomographie par rayons X reste la modalité d'imagerie la plus répandue dans le domaine médical mais est également utilisée de façon croissante, voire exponentielle, dans de nombreux autres domaines, que ce soit en biologie ou en sciences de matériaux.La tomographie par rayons X est en effet passée d'une technique 2D à une technique 3D, et l’amélioration de sa résolution spatiale jusqu’à des résolutions micrométrique ou nanométrique, a permis de développer des techniques de choix, connues sous le nom de micro-CT et nano-CT, pour l’imagerie microscopique 3D de divers matériaux [1]. De plus, outre le contraste d’absorption à la base de la tomographie standard, il est possible d’obtenir, sous certaines conditions, différents contrastes et ainsi des données quantitatives sur la composition des échantillons. Nous introduirons brièvement le principe de la tomographie par rayons X, qui repose sur la combinaison d'instruments à rayons X et d'algorithmes de reconstruction tomographique et introduirons la percée récente des méthodes d’apprentissage profond dans ce domaine