Albert Claude Boccara

Image transmission through an opaque material

Optical imaging relies on the ability to illuminate an object, collect and analyse the light it scatters or transmits. Propagation through complex media such as biological tissues was so far believed to degrade the attainable depth, as well as the resolution for imaging, because of multiple scattering. This is why such media are usually considered opaque. Recently, we demonstrated that it is possible to measure the complex mesoscopic optical transmission channels that allow light to traverse through such an opaque medium. Here, we show that we can optimally exploit those channels to coherently transmit and recover an arbitrary image with a high fidelity, independently of the complexity of the propagation.

State-of-the art of acousto-optic sensing and imaging of turbid media

Acousto-optic (AO) is an emerging hybrid technique for measuring optical contrast in turbid media using coherent light and ultrasound (US). A turbid object is illuminated with a coherent light source leading to speckle formation in the remitted light. With the use of US, a small volume is selected,which is commonly referred to as the tagging volume. This volume acts as a source of modulated light, where modulation might involve phase and intensity change. The tagging volume is created by focusing ultrasound for good lateral resolution; the axial resolution is accomplished by making either the US frequency, amplitude, or phase time-dependent. Typical resolutions are in the order of 1 mm. We will concentrate on the progress in the field since 2003. Different schemes will be discussed to detect the modulated photons based on speckle detection, heterodyne detection, photorefractive crystal (PRC) assisted detection, and spectral hole burning (SHB) as well as Fabry-Perot interferometers. The SHB and Fabry-Perot interferometer techniques are insensitive to speckle decorrelation and therefore suitable for in vivo imaging. However, heterodyne and PRC methods also have potential for in vivo measurements. Besides measuring optical properties such as scattering and absorption, AO can be applied in fluorescence and elastography applications.

Retrieving time-dependent Green's functions in optics with low-coherence interferometry

We report on the passive measurement of time-dependent Greens functions in optics with low-coherence interferometry. Inspired by previous studies in acoustics and seismology, we show how the correlations of a broadband and incoherent wave-field can directly yield the Greens functions between scatterers of a complex medium.

Elastography of multicellular aggregates submitted to osmo-mechanical stress

Tumors are subjected to mechanical stress generated by their own growth in a confined environment, and by their surrounding tissues. Recent works have focused on the study of the growth of spherical aggregates of cells, spheroids, under controlled confinement or stress. In this study we demonstrate the measurement of spatially and temporally resolved deformation maps inside spheroids while applying an osmo-mechanical stress. We use full field optical coherence tomography, a high resolution imaging technique well suited for real-time measurements of deformation in living tissues under stress. Using the spherical symmetry of the experiment, we compare our data to a mechanical modeling of the spheroid as a continuous medium. We estimate the viscoelastic parameters of spheroids and discuss the apparent tissue anisotropy after the osmo-mechanical stress.

Adaptive optics full-field optical coherence tomography

Abstract. We describe a simple and compact full-field optical coherence tomography (FFOCT) setup coupled to a transmissive liquid crystal spatial light modulator (LCSLM) to induce or correct aberrations. To reduce the system complexity, strict pupil conjugation was abandoned because low-order aberrations are often dominant. We experimentally confirmed a recent theoretical and experimental demonstration that the image resolution was almost insensitive to aberrations that mostly induce a reduction of the signal level. As a consequence, an image-based algorithm was applied for the optimization process by using the FFOCT image intensity as the metric. Aberration corrections were demonstrated with both an USAF resolution target and biological samples for LCSLM-induced and sample-induced wavefront distortions.

Full-field interferometry for counting and differentiating aquatic biotic nanoparticles: from laboratory to Tara Oceans.

There is a huge abundance of viruses and membrane vesicles in seawater. We describe a new full-field, incoherently illuminated, shot-noise limited, common-path interferometric detection method that we couple with the analysis of Brownian motion to detect, quantify, and differentiate biotic nanoparticles. We validated the method with calibrated nanoparticles and homogeneous DNA or RNA viruses. The smallest virus size that we characterized with a suitable signal-to-noise ratio was around 30 nm in diameter. Analysis of Brownian motions revealed anisotropic trajectories for myoviruses.We further applied the method for vesicles detection and for analysis of coastal and oligotrophic samples from Tara Oceans circumnavigation.

Ultrahigh resolution imaging of cellular dynamics in explanted corneas and retinas with ocular pathologies using dynamic full-field OCT (Conference Presentation)

Full-Field Optical Coherence Tomography (FF-OCT) reveals submicrometric morphological details in retinal explants without the use of contrast agents. Dynamic FF-OCT (D-FF-OCT) takes advantage of the temporal evolution of the local FF-OCT signal to reveal a movement-dependent contrast inside tissues, mostly relying on cellular motility. Compared to regular FF-OCT images, the relative contrast from stationary structures such as nerve fibers is reduced, and contrast inside cells is enhanced, revealing many more cells, as well as the position of nuclei, and cell metabolism.nWe used a multimodal FF-OCT, D-FF-OCT and fluorescence microscope to compare and identify the structures observed in D-FF-OCT, which allowed us to reconstruct the full 3-D micrometric organization of corneal and retinal explants. In healthy explants, this multimodal association allows the label-free specific detection of all cell populations, except from the Mueller cells, and of several structural features such as nerve and collagen fibers, and pedicles and spherules. D-FF-OCT also accesses several functional contrasts (relying on metabolism, mechanical and electrical activity) that can be combined to monitor the tissue health over time.nIt is anticipated that such a combination of static and dynamic OCT information may be used in vivo in future for the early detection of ocular pathologies. To this end, we tried here to foster our understanding of the progression and occurrence of such diseases in animal models. We notably used this optical system to follow the evolution of stem cells injected in the cornea and to assess the concentration of macrophages in retinas with inflammation.

Static and dynamic full field OCT: an endogenous biomaker? (Conference Presentation)

Full Field OCT (FFOCT) is a shot noise limited interferometric microscopy technique that uses incoherent light and has proved to be an effective diagnostic tool in terms of sensitivity and specificity. We have used the FFOCT setup built by LLTech for the analysis of various cancerous tissues corresponding to the following organs: breast, skin, prostate, lungs, ENT, bladder, brain etc. The scores obtained were found in the range between 80 and 98%. To do better and to provide informations that the histology does not carry we have studied, using the same setup, the temporal dependence of our signals which we found to be related to the cellular metabolism. We have used the new high speed and high full well capacity of the Adimec camera to achieve a time analysis ranging between 2 and a few thousands of ms. We thus obtain a new contrast which constitutes a biomarker at the sub-cellular scale. We monitor the characteristic frequencies and amplitude of the signal and display them on the images of the tissues using a new processing code of the time series. This metabolic contrast also reveal the evolution of the activity of cancer cells under treatments such as chemotherapy. We will illustrate this new approach through examples of cancer tissues that are planned to be used as intraoperative tools.

The role of prefrontal cortex in a moral judgment task using functional near-infrared spectroscopy

Understanding the neural basis of moral judgment (MJ) and human decision‐making has been the subject of numerous studies because of their impact on daily life activities and social norms. Here, we aimed to investigate the neural process of MJ using functional near‐infrared spectroscopy (fNIRS), a noninvasive, portable, and affordable neuroimaging modality.

In vivo imaging through the entire thickness of human cornea by full-field optical coherence tomography

Despite obvious improvements in visualization of the in vivo cornea through the faster imaging speeds and higher axial resolutions, cellular imaging stays unresolvable task for OCT, as en face viewing with a high lateral resolution is required. The latter is possible with FFOCT, a method that relies on a camera, moderate numerical aperture (NA) objectives and an incoherent light source to provide en face images with a micrometer-level resolution. Recently, we for the first time demonstrated the ability of FFOCT to capture images from the in vivo human cornea1. In the current paper we present an extensive study of appearance of healthy in vivo human corneas under FFOCT examination. En face corneal images with a micrometer-level resolution were obtained from the three healthy subjects. For each subject it was possible to acquire images through the entire corneal depth and visualize the epithelium structures, Bowman’s layer, sub-basal nerve plexus (SNP) fibers, anterior, middle and posterior stroma, endothelial cells with nuclei. Dimensions and densities of the structures visible with FFOCT, are in agreement with those seen by other cornea imaging methods. Cellular-level details in the images obtained together with the relatively large field-of-view (FOV) and contactless way of imaging make this device a promising candidate for becoming a new tool in ophthalmological diagnostics.