Biomedical subjects

P Cloetens

Publications and source records attributed to P Cloetens.

11 recordsLinked to original sources

PubMed2006

On qualitative and quantitative analysis in analyser-based imaging.

Using rigorous wave-optical formalism, a general expression is obtained for the image intensity distribution in combined analyser-based/propagation-based phase-contrast imaging. This expression takes into account partial coherence of the wave incident on the object as well as the finite resolution of the detector system. Using this general expression, two approaches based on the geometrical optics and weak-object approximations are applied to derive simple solutions to the inverse problem of reconstruction of the phase and amplitude of the object wave. With the help of numerical experiments, the two approaches are compared in terms of their validity conditions and are shown to impose certain restrictions on the properties of the object wave. In particular, it is shown that violation of the validity conditions of the geometrical optics or weak-object approximations results in the appearance of strong reconstruction artefacts in the transmitted intensity near the edges of the objects. The effect of the incident wavefront non-uniformity due to imperfections of the imaging set-up on image formation and phase/amplitude reconstruction is also discussed. A solution to this problem is proposed in the form of a multi-image phase/amplitude reconstruction algorithm based on the geometrical optics approximation. This algorithm and an algorithm based on the weak-object approximation are applied to simulated and experimental images of fibres.

Journal Article↗

PubMed2005

Direct evidence of nanometric invasionlike grain boundary penetration in the A(1)/Ga system.

We report the first in situ results of deformation during grain boundary penetration in the A(1)/Ga system, obtained with a novel, nondestructive hard x-ray synchrotron projection microscopy technique. Focusing the beam to a state-of-the-art spot size of 90 x 90 nm(2), we demonstrate that penetration is accompanied by continuous relative separation of the Al grains of the same final amplitude as the final Ga layer thickness in the absence of external stress. The formation of nanometric intergranular liquid layers is originated by a crack propagation process and inherently implies the presence of weak stress levels.

Journal Article↗

PubMed2004

X-ray high-resolution vascular network imaging.

This paper presents the first application of high-resolution X-ray synchrotron tomography to the imaging of large microvascular networks in biological tissue samples. This technique offers the opportunity of analysing the full three-dimensional vascular network from the micrometre to the millimetre scale. This paper presents the specific sample preparation method and the X-ray imaging procedure. Either barium or iron was injected as contrast agent in the vascular network. The impact of the composition and concentration of the injected solution on the X-ray synchrotron tomography images has been studied. Two imaging modes, attenuation and phase contrast, are compared. Synchrotron high-resolution computed tomography offers new prospects in the three-dimensional imaging of in situ biological vascular networks.

Animals↗

PubMed2004

Quantification of micrometre-sized porosity in quasicrystals using coherent synchrotron radiation imaging.

Phase contrast radiography has been applied to investigate porosity in the bulk of quasicrystals. The pores act on X-rays as lenses, leading to drastic changes in the phase contrast images of pores. Depending on the recording conditions and pore features, different imaging regimes are accessed. The variation of the contrast makes the direct characterization of pores from image data, in terms of a precise determination of their size and volume, unreliable. The contrast in Fresnel diffraction images of pores was thus investigated with the support of numerical simulations. A phase retrieval procedure was carried out in order to obtain the correct information from the pore images.

Journal Article↗

PubMed2000

Phase imaging using highly coherent X-rays: radiography, tomography, diffraction topography.

Several hard X-rays imaging techniques greatly benefit from the coherence of the beams delivered by the modern synchrotron radiation sources. This is illustrated with examples recorded on the 'long' (145 m) ID19 'imaging' beamline of the ESRF. Phase imaging is directly related to the small angular size of the source as seen from one point of the sample ('effective divergence' approximately microradians). When using the ;propagation' technique, phase radiography and tomography are instrumentally very simple. They are often used in the 'edge detection' regime, where the jumps of density are clearly observed. The in situ damage assessment of micro-heterogeneous materials is one example of the many applications. Recently a more quantitative approach has been developed, which provides a three-dimensional density mapping of the sample ('holotomography'). The combination of diffraction topography and phase-contrast imaging constitutes a powerful tool. The observation of holes of discrete sizes in quasicrystals, and the investigation of poled ferroelectric materials, result from this combination.

Journal Article↗

PubMed2000

Perspectives in three-dimensional analysis of bone samples using synchrotron radiation microtomography.

In this paper we present a methodology based on 3D synchrotron radiation microtomography to analyze non-destructively 3D bone samples. After a technical presentation of the imaging system and the image analysis techniques, we report results on three-dimensional analysis of vertebral samples from women of different ages. The new capabilities of this technique for the investigation of bone are discussed. They include a high spatial resolution down to the micron level, a high density resolution allowing a local quantification of bone mineralization, phase contrast imaging and advances in 3D image analysis.

Adult↗

PubMed1999

A synchrotron radiation microtomography system for the analysis of trabecular bone samples.

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.

Aged↗

PubMed1998

Conserving the coherence and uniformity of third-generation synchrotron radiation beams: the case of ID19, a 'long' beamline at the ESRF.

The lateral coherence length is of the order of 100 micron at the 'long' (145 m) ID19 beamline of the ESRF, which is mainly devoted to imaging. Most of the optical elements located along the X-ray path can thus act as ;phase objects', and lead to spurious contrast and/or to coherence degradation, which shows up as an enhanced effective angular size of the source. Both the spurious contrast and the coherence degradation are detrimental for the images (diffraction topographs, tomographs, phase-contrast images) produced at this beamline. The problems identified and the way they were solved during the commissioning of ID19 are reported. More particularly, the role of the protection foils located in the front end, the beryllium windows, the filters and the monochromator defects (scratches, dust, small vibrations) is discussed.

Journal Article↗

PubMed1998

Submicrometre resolution phase-contrast radiography with the beam from an X-ray waveguide.

Experimental data with unprecedented submicrometre resolution obtained in a phase-contrast radiography experiment in a magnifying configuration are presented. The term 'phase contrast' here indicates that the phase retardation of coherent light in matter was utilized as the contrast mechanism. The coherent and divergent beam exiting an X-ray waveguide was used in a lensless configuration to magnify spatial variations in optical path length up to several hundred times. The defocused image of a nylon fibre was measured with a resolution of 0.14 micro m at the object. Sufficient contrast was found for exposure times of 0.1 s, i.e. in the regime for real-time studies.

Journal Article↗

PubMed1998

Micro-CT examinations of trabecular bone samples at different resolutions: 14, 7 and 2 micron level.

Tomographic techniques are attractive for the investigation of trabecular bone architecture. Using either conventional X-ray sources or synchrotron sources currently allows the acquisition of 3D images in a wide range of spatial resolution that may be as small as a few micrometers. Since it is technically possible to examine trabecular architecture at different scales, a question is to know what type of information it is possible to get at each scale. For this purpose, a series of ten vertebrae samples from healthy females of different ages (33 to 90) was imaged at various resolutions on three different micro-CT systems (cubic voxel size respectively 14, 6.7 and 1.4 microm). The comparison of morphometric parameters extracted from the different images is in agreement with simulation results on the influence of spatial resolution on structure parameters. The conclusion is that a 14 microm voxel size gives a reasonably good parameterisation of trabecular architecture. Besides the synchrotron radiation 2 microm level images reveal interesting features on the irregularities and rupture of trabecular surface, and on remodeling zones.

Adult↗

PubMedDate not supplied

Synchrotron x-ray microtomographic investigation of mineral concentrations at micrometre scale in sound and carious enamel.

Synchrotron X-ray microtomography (XMT) was used to measure the linear attenuation coefficient (LAC) for 1.9-microm sidelength voxels within approximal brown spot lesions and sound human enamel. XMT demonstrated three-dimensional features, notably sheets with approximately 30 microm periodicity having low LAC, identified as regions of demineralization corresponding to Retzius lines. Quantitative three-dimensional measurements of mineral concentration, derived from LAC with assumption of a single model composition, were consistent with previous measurements of sound and carious enamel from microradiographic projections. The uncertainty in measurements of mineral concentration and mineral fraction volume was investigated by modelling enamel with a range of composition and component densities. This analysis showed that, although mineral concentration can be determined from LAC with an error of <0.2 g cm(-3), the variation in pore fraction volume within caries lesions cannot be reliably determined from X-ray attenuation measurements alone.

Apatites↗