Carole Deumie

Considering sources and detectors distributions for quantitative photoacoustic tomography

Photoacoustic tomography (PAT) is a hybrid imaging modality that takes advantage of high optical contrast brought by optical imaging and high spatial resolution brought by ultrasound imaging. However, the quantification in photoacoustic imaging is challenging. Multiple optical illumination approach has proven to achieve uncoupling of diffusion and absorption effects. In this paper, this protocol is adopted and synthetic photoacoustic data, blurred with some noise, were generated. The influence of the distribution of optical sources and transducers on the reconstruction of the absorption and diffusion coefficients maps is studied. Specific situations with limited view angles were examined. The results show multiple illuminations with a wide field improve the reconstructions.

Human graft cornea and laser incisions imaging with micrometer scale resolution full-field optical coherence tomography

Micrometer scale resolution full-field optical coherence tomography (FF-OCT) is developed for imaging human graft corneas. Three-dimensional (3-D) images with ultrahigh resolution (respectively, 1 and 1.5 μm in the axial and transverse directions), comparable to traditional histological sections, are obtained allowing the visualization of the cells and the precise structure of the different layers that compose the tissue. The sensitivity of our device enables imaging the entire thickness of the cornea, even in edematous corneas more than 800 μm thick. Furthermore, we provide tomographic 3-D images of laser incisions inside the tissue at various depths without slicing the studied corneas. The effects of laser ablations can be observed, along various optical sections, directly in the bulk of the sample with high accuracy, providing information on the interface quality and also imaging tiny changes of the tissue structure. FF-OCT appears to be a powerful tool for subcellular imaging of the corneal structure and pathologies on the entire thickness of the tissue as well as interface quality and changes in the collagen structure due to laser incisions on ex vivo human cornea.

Elliptically polarized light for depth resolved optical imaging

It is shown that using elliptically polarized light permits selecting well-defined subsurface volumes in a turbid medium. This suggests the possibility of probing biological tissues at specific depths. First, we present the method and preliminary results obtained on an Intralipid phantom. We next report on the method’s performance on a biological phantom (chicken breast) and, finally, on the exposed cortex of an anesthetized rat.

Overlapping of roughness spectra measured in macroscopic (optical) and microscopic (AFM) bandwIDths

Light scattering and Atomic Force Microscopy (AFM) are used together to analyze surface roughness in a very wide frequency bandwidth, extending from macroscopic (optical) to microscopic (AFM) scales. The two techniques are shown to be in large agreement since the roughness spectra overlap at intersection of bandwidths. A particular behavior of roughness is emphasized that permits to predict scattering at very short wavelengths. Thin film materials obtained by different techniques (IAD, Ion Plating, EB) are also investigated via a comparison of roughness spectra measured before and after coating in all bandwidths.

Depth probing of diffuse tissues controlled with elliptically polarized light

Abstract. Polarization gating is a popular technique in biomedical optics. It is widely used to inspect the surface of the tissues (under colinear or cocircular detection) or instead to probe the volume (cross-linear detection), without information on the probed depth. Elliptical polarization is introduced to explore the possibility of probing diffuse tissues at selective depths. A thorough Monte Carlo simulation study shows complete correlation between the probed depths and the ellipticity of the polarized light, for a medium with known optical properties. Within a wide range of optical parameters, a linear relation between the backscattered intensity and the depth extension of the probed volume was found whatever the polarization used, but with a controlled extension depending on the ellipticity.

Light scattering from human corneal grafts: Bulk and surface contribution

The cornea is the only transparent tissue in the body. The transparency is the main characteristic of the corneal tissue, and depends not only on the transmission coefficient but also on the losses by scattering and absorption. The scattering properties of the cornea tissues become one of the most important parameters in the case of the corneal graft. These scattering properties are studied in this paper in the reflected half area, similar to the diagnosis configuration. We quantify the influence of the cornea thickness and of the epithelial layer on scattering level. The technique of ellipsometry on scattered field is also used to analyze the polarization properties in order to determine the origin of scattering (surface and/or bulk).

Comparison of polarized light penetration depth in scattering media

A polarization-sensitive Monte Carlo model is used to investigate differently polarized light illuminations on their degree of polarization (DOP) depth evolution in a semi-infinite scattering medium. The three-dimensional simulations show that circular polarized light maintains its initial polarization state longer than elliptical or linear polarized light. It was revealed that elliptical polarization can be tuned so that its DOP depth evolution can be precisely chosen between the penetration depths of linearly and circularly polarized light.

Depth selectivity in biological tissues by polarization analysis of backscattered light

Depth selectivity is crucial for accurate depth volume probing in vivo in a large number of medical applications such as brain monitoring. Polarization gating has been widely used to analyze biological tissues. It is shown that using polarized light allows probing tissues on a specific depth depending on the polarization illumination type (linearly, circularly) and the tissues properties. However, accurate depth investigation of the tissue requires a high selectivity of the probed depth. We propose and simulate the use of different elliptically polarized illuminations for continuous depth examination between linearly and circularly polarized illumination. Monte Carlo simulations verify that circularly polarized illumination penetrates deeper than linearly polarized illumination in biological scattering media. Furthermore, we show that elliptically polarized light can be tuned in its penetration depth continuously between the penetration depth of linearly polarized light and circularly polarized light. Experimental results obtained on phantoms mimicking in vivo situations are presented.

Study of varnish layers with optical coherence tomography in both visible and infrared domains

Optical Coherence Tomography (OCT) is an attractive technique to study works of art because it allows non-destructive and contactless analysis. In the case of musical instruments, the study of wood finishes could give interesting information as the thicknesses of the layers, the number of layers and the presence of fillers. A time-domain full-field OCT, achieving high resolution, is used in both visible and near infrared ranges to characterize semi-transparent layers containing scattering particles as charged varnish layers. We present OCT measurements on wood varnished with different coatings. We show that the detection of pigment particles is dependent of the spectral range and that both spectral domains allow to reach micrometer-scale spatial resolutions.

Sun protection and hydration of stratum corneum: a study by 2-D differential method.

The stratum corneum is the outermost layer of the skin. Its components and its morphology (such as the size of its cells) play a role in sun protection, and it has been noted that the stratum corneum hydration can change these properties. Sunscreens, applied on the skin, can be more or less effective depending on the stratum corneum characteristics. We therefore propose to simulate the quality of the sun protection and the effect of the stratum corneum hydration on the sun protection.