Biomedical subjects

Arnaud Dubois

Publications and source records attributed to Arnaud Dubois.

7 recordsLinked to original sources

PubMed2006

Investigation of optical coherence tomography as an imaging modality in tissue engineering.

Monitoring cell profiles in 3D porous scaffolds presents a major challenge in tissue engineering. In this study, we investigate optical coherence tomography (OCT) as an imaging modality to monitor non-invasively both structures and cells in engineered tissue constructs. We employ time-domain OCT to visualize macro-structural morphology, and whole-field optical coherence microscopy to delineate the morphology of cells and constructs in a developing in vitro engineered bone tissue. The results show great potential for the use of OCT in non-invasive monitoring of cellular activities in 3D developing engineered tissues.

Adolescent↗

PubMed2006

[Full-field OCT].

Optical coherence tomography (OCT) is an emerging technique for imaging of biological media with micrometer-scale resolution, whose most significant impact concerns ophthalmology. Since its introduction in the early 1990's, OCT has known a lot of improvements and sophistications. Full-field OCT is our original approach of OCT, based on white-light interference microscopy. Tomographic images are obtained by combination of interferometric images recorded in parallel by a detector array such as a CCD camera. Whereas conventional OCT produces B-mode (axially-oriented) images like ultrasound imaging, full-field OCT acquires tomographic images in the en face (transverse) orientation. Full-field OCT is an alternative method to conventional OCT to provide ultrahigh resolution images (approximately 1 microm), using a simple halogen lamp instead of a complex laser-based source. Various studies have been carried, demonstrating the performances of this technology for three-dimensional imaging of ex vivo specimens. Full-field OCT can be used for non-invasive histological studies without sample preparation. In vivo imaging is still difficult because of the object motions. A lot of efforts are currently devoted to overcome this limitation. Ultra-fast full-field OCT was recently demonstrated with unprecedented image acquisition speed, but the detection sensitivity has still to be improved. Other research directions include the increase of the imaging penetration depth in highly scattering biological tissues such as skin, and the exploitation of new contrasts such as optical birefringence to provide additional information on the tissue morphology and composition.

Tomography, Optical Coherence↗

PubMed2004

Ultrahigh-resolution full-field optical coherence tomography.

We have developed a white-light interference microscope for ultrahigh-resolution full-field optical coherence tomography of biological media. The experimental setup is based on a Linnik-type interferometer illuminated by a tungsten halogen lamp. En face tomographic images are calculated by a combination of interferometric images recorded by a high-speed CCD camera. Spatial resolution of 1.8 microm x 0.9 microm (transverse x axial) is achieved owing to the extremely short coherence length of the source, the compensation of dispersion mismatch in the interferometer arms, and the use of relatively high-numerical-aperture microscope objectives. A shot-noise-limited detection sensitivity of 90 dB is obtained in an acquisition time per image of 4 s. Subcellular-level images of plant, animal, and human tissues are presented.

Animals↗

PubMed2004

Effects of phase change on reflection in phase-measuring interference microscopy.

We show by analytical and numerical calculations that the phase change on reflection that occurs in interference microscopy is almost independent of the numerical aperture of the objective. The shift of the microscope interferogram response due to the phase change on reflection, however, increases with the numerical aperture. Measurements of the interferogram shift are made with a Linnik interference microscope equipped with various numerical-aperture objectives and are reported and compared with theory.

Journal Article↗

PubMed2004

Initiation of gastrulation in the mouse embryo is preceded by an apparent shift in the orientation of the anterior-posterior axis.

BACKGROUND: It is generally assumed that the migration of anterior visceral endoderm (AVE) cells from a distal to a proximal position at embryonic day (E)5.5 breaks the radial symmetry of the mouse embryo, marks anterior, and conditions the formation of the primitive streak on the opposite side at E6.5. Transverse sections of a gastrulating mouse embryo fit within the outline of an ellipse, with the primitive streak positioned at one end of its long axis. How the establishment of anterior-posterior (AP) polarity relates to the morphology of the postimplantation embryo is, however, unclear. RESULTS: Transverse sections of prestreak E6.0 embryos also reveal an elliptical outline, but the AP axis, defined by molecular markers, tends to be perpendicular to the long axis of the ellipse. Subsequently, the relative orientations of the AP axis and of the long axis change so that when gastrulation begins, they are closer to being parallel, albeit not exactly aligned. As a result, most embryos briefly lose their bilateral symmetry when the primitive streak starts forming in the epiblast. CONCLUSIONS: The change in the orientation of the AP axis is only apparent and results from a dramatic remodeling of the whole epiblast, in which cell migrations take no part. These results reveal a level of regulation and plasticity so far unsuspected in the mouse gastrula.

Animals↗

PubMed2004

Ocular tissue imaging using ultrahigh-resolution, full-field optical coherence tomography.

PURPOSE: Ultrahigh-resolution, full-field optical coherence tomography (OCT), which uses a white light source, allows bidimensional, noninvasive tomographic imaging without scanning. The goal of the present study was to apply full-field OCT to ocular tissue imaging in an attempt to explore the capabilities of the technique. METHODS: This full-field OCT system uses a Linnik-type interferometer with a tungsten-halogen source. The spatial resolution is 0.9 x 0.7 microm (transverse x axial). Unstained tissue samples (cornea, lens, retina, choroid, and sclera) and whole, unfixed eyes of rat, mouse, and pig were examined under immersion. A charge-coupled device (CCD) camera recorded a pair of interferometric images that were combined to display en face (i.e., in the x-y plane) tomographic images in real time. The acquisition time per tomographic image, which includes summation of 10 raw images, was on the order of 1 s. Postprocessing allows volumetric navigation through the image stack as well as three-dimensional (3D) imaging. RESULTS: Cellular-level resolution was achieved in isolated tissue samples. En face (x-y) images revealed corneal epithelial and stromal cells, lens fibers, nerve fibers, major vessels, and retinal pigment epithelial cells. In x-z reconstructions, cellular layers within the cornea and retina and arterioles and venules were clearly defined. Transscleral retinal imaging was achieved in albino animals. CONCLUSIONS: Ultrahigh-resolution, full-field OCT allows cellular-level imaging of unstained ocular tissues with high penetration depth. Although the current system is unsuitable for clinical use, this simple technique has potential for in vivo ocular examination, for which a new system is currently under development.

Anatomy, Cross-Sectional↗

PubMed2002

High-resolution full-field optical coherence tomography with a Linnik microscope.

We describe an original microscope for high-resolution optical coherence tomography applications. Our system is based on a Linnik interference microscope with high-numerical-aperture objectives. Lock-in detection of the interference signal is achieved in parallel on a CCD by use of a photoelastic birefringence modulator and full-field stroboscopic illumination with an infrared LED. Transverse cross-section (en-face, or XY) images can be obtained in real time with better than 1-microm axial (Z) resolution and 0.5-microm transverse (XY) resolution. A sensitivity of approximately 80 dB is reached at a 1-image/s acquisition rate, which allows tomography in scattering media such as biological tissues.

Microscopy, Interference↗