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L’endoscopie est un examen médical qui permet de visualiser l’intérieur des organes creux. Ce chapitre présente les fondements du traitement d’images endoscopiques ainsi que les solutions techniques et méthodologiques les plus récentes d’acquisition de données multispectrales et/ou multimodales et de mosaïquage d’images visant à répondre aux enjeux médico-techniques d’amélioration de l’efficacité de détection in vivo des lésions.

An asymmetric cryptosystem is presented for encrypting multiple images in gyrator transform domains. In the encryption approach, the devil’s spiral Fresnel lens variable pure phase mask is first designed for each image band to be encrypted by using devil’ mask, random spiral phase and Fresnel mask, respectively. Subsequently, a novel random devil’ spiral Fresnel transform in optical gyrator transform is implemented to achieved the intermediate output. Then, the intermediate data is divided into two masks by employing random modulus decomposition in the asymmetric process. Finally, a random permutation matrix is utilized to obtain the ciphertext of the intact algorithm. For the decryption approach, two divided masks (private key and ciphertext) need to be imported into the optical gyrator input plane simultaneously. Some numerical experiments are given to verify the effectiveness and capability of this asymmetric cryptosystem.

International audience; In the context of cutaneous carcinoma diagnosis based on in vivo optical biopsy, Diffuse Reflectance (DR) spectra, acquired using a Spatially Resolved (SR) sensor configuration, can be analyzed to distinguish healthy from pathological tissues. The present contribution aims at studying the depth distribution of SR-DR-detected photons in skin from the perspective of analyzing how these photons contribute to acquired spectra carrying local physiological and morphological information. Simulations based on modified Cuda Monte Carlo Modeling of Light transport were performed on a five-layer human skin optical model with epidermal thickness, phototype and dermal blood content as variable parameters using (i) wavelength-resolved scattering and absorption properties and (ii) the geometrical configuration of a multi-optical fiber probe implemented on an SR-DR spectroscopic device currently used in clinics. Through histograms of the maximum probed depth and their exploitation, we provide numerical evidence linking the characteristic penetration depth of the detected photons to their wavelengths and four source–sensor distances, which made it possible to propose a decomposition of the DR signals related to skin layer contributions.

International audience; A spatially resolved multimodal spectroscopic device was used on a two-layered “hybrid” model made of ex vivo skin and fluorescent gel to investigate the effect of skin optical clearing on the depth sensitivity of optical spectroscopy. Time kinetics of fluorescence and diffuse reflectance spectra were acquired in four experimental conditions: with optical clearing agent (OCA) 1 made of polyethylene glycol 400 (PEG-400), propylene glycol and sucrose; with OCA 2 made of PEG-400 and dimethyl sulfoxide (DMSO); with saline solution as control and a “dry” condition. An increase in the gel fluorescence back reflected intensity was measured after optical clearing. Effect of OCA 2 turned out to be stronger than that of OCA 1, possibly due to DMSO impact on the stratum corneum keratin conformation. Complementary experimental results showed increased light transmittance through the skin and confirmed that the improvement in the depth sensitivity of the multimodal spectroscopic approach is related not only to the dehydration and refractive indices matching due to optical clearing, but also to the mechanical compression of tissues caused by the application of the spectroscopic probe.

Skin optical clearing is the method providing the increase of the depth and the contrast of non-invasive optical techniques. Dehydration is one of the possible mechanisms of optical clearing that may lead to reduce in both skin thickness and backscattering. However, the contribution of dehydration of skin to the collimated transmittance spectra is not studied in details. This paper presents the results of such study with rat skin ex vivo. Dehydration of skin sample was provided using a fan with a heater. Throughout the experiment, a warm air flux (~ 36 °C) was directed to the dermal side of each sample. Transmittance spectra were obtained using a system of two optical fibers equipped with collimators in the wavelength range of 400-800 nm. The thickness was measured during dehydration using a micrometer. As a result, it was found that a decrease in the thickness of the skin sample during dehydration led to an increased light transmission through the skin (an 11-fold increase at λ= 700 nm), and, at the same time, to an increase in the light attenuation coefficient μt due to an increase in the concentration of scatterers in the skin per unit volume.

International audience; In this paper, a novel optical encryption algorithm for multiple images based on chaos and DNA-blend in gyrator transform domain is proposed. Firstly, the multispectral image is divided into eight parts regularly. Subsequently the pixel positions of the blocked images are scrambled according to the pixel values of the chaotic sequences generated by 4D Lorenz system. Furthermore, eight kinds of deoxyribonucleic acid (DNA) matrices in binary form are also considered and utilized among the eight blocked fragments. Finally, the scrambled images are encoded and transformed in optical gyrator transform light field and the ciphertext is scrambled by Arnold transform to enhance the security. The proposed cryptosystem can be implemented by an electro-optical hybrid setup. Some parameters of the chaos system and gyrator transform serves as the extra keys of the encryption scheme. Some numerical simulations are implemented to testify the validity and robustness of the proposed cryptosystem for multiple images.

Published in SPIE Proceedings Volume 11640, Optical Interactions with Tissue and Cells XXXII, 116400H (2021); International audience; In the context of cutaneous carcinoma in vivo diagnosis, Diffuse Relectance (DR) acquired using Spatially Resolved (SR) optical biopsy, can be analysed to discard healthy from pathological areas. Indeed, carcinogenesis induces local morphological and metabolic changes affecting the skin optical answer to white light excitation. The present contribution aims at studying the epidermis thickness impact on the path and propagation depth distribution of DR photons in skin in the perspective of analyzing how these photons contribute to the corresponding acquired spectra carrying local physiological information from the visited layers. Modified CudaMCML-based simulations were performed on a five-layer human skin optical model using (i) wavelength-resolved scattering and absorption properties and (ii) the geometrical configuration of a multi-optical fiber probe implemented on a SR-DR spectroscopic device currently used in clinics. Through maps of scattering events and histograms of maximum probed depth, we provide numerical evidences linking the characteristic penetration depth of the detected photons to their wavelengths and four source-sensor distances for thin, intermediate and wide skin thicknesses model. The study provides qualitative and quantitative tools that can be useful during the design of an optical SR-DR spectroscopy biopsy device.

A novel chaotic cryptosystem for hyperspectral image, in this paper, is proposed by using a 4D hyperchaotic system in gyrator transform domains. In encryption process, a random spiral phase function (RSPF) is designed to generate variable spiral phase mask, which can be used for phase encoding with the hyperspectral image. Subsequently, the 4D hyperchaotic system is utilized to generate the chaotic sequences and these chaotic data is employed in designing RSPF, scrambling the hyperspectral image and synthesizing complex ciphertext, respectively. Finally, an improved spiral phase transform (SPT) in gyrator domains is implemented to obtain the ciphertext. To enhance the security of the encryption scheme, the ciphertext is reorganized according to the hyperchaotic attractor. Theoretical simulation analysis is given to demonstrate the validity and robustness of the proposed cryptosystem.

International audience; In this study, the changes in Spatially Resolved Diffuse Reflectance and AutoFluorescence spectra acquired on ex vivo human skin during optical clearing process (topical application) are investigated and their impact on skin optical properties (absorption, scattering and fluorescence) analyzed using inverse problem solving and multidimensional data processing approaches.

In the context of cutaneous carcinoma in vivo diagnosis, Diffuse Relectance (DR) and skin endogenous fluores- cence (AF) spectra, acquired using Spatially Resolved (SR) multimodal optical biopsy, can be analysed to discard healthy from pathological areas. Indeed, carcinogenesis induces morphological and metabolic changes affecting endogenous fluorophores such as for instance elastosis and enzymatic degradation of collagen fluorescence in the dermis or decreased NADH fluorescence in the epidermis. The present contribution aims at studying the path and propagation depth distribution of DR and AF photons in skin in the perspective of analyzing how these photons contribute to the corresponding acquired spectra carrying local physiological information. Modified CudaMCML-based simulations were performed on a five-layer human skin optical model with (i) wavelength resolved scattering, absorption and endogenous fluorescence properties and (ii) multiple fiber optic probe ge- ometrical configuration of a SR-DR and -AF spectroscopic device. The simulation results provided numerical evidences of the behaviour of detected photons in the tissue. In particular, we succeeded in linking the character- istic penetration depth of the detected photons to their wavelengths and the source-sensor distance. In addition, we managed to identify the region where the fluorescence events associated with the AF spectrum photon take place. The study provides qualitative and quantitative tools that can be useful during the design of an optical multimodal biopsy device.

Skin cancers including carcinomas and melanomas are currently the most common cancers in fair skinned humans. Histopathology, requiring invasive tissue biopsy and processing, is the gold standard for cancer diagnosis. Optical Coherence Tomography (OCT) has emerged as a label-free, non-traumatic and non-invasive method that can be used in vivo to image skin tissues (from stratum corneum to dermis) and therefore contribute to skin cancer diagnosis. Some of the major limitations of OCT imaging techniques are a lower resolution compared to histology and a limited penetration depth due to skin tissues’ strong optical scattering. Optical clearing has been investigated for several years as one of the solutions to overcome these problems by inducing a reversible decreased scattering and thus allowing a better contrast and an improved light penetration depth within biological tissues. Clearing is achieved using optical clearing agents (OCA) combined with chemical enhancers (used to better pass through the stratum corneum layer). As a first step, the current study aims at defining the quantitative features (intensity profile, image statistics, texture descriptors) that are best suited to quantify optical clarification kinetics from images acquired using Linefield Confocal-OCT (LC-OCT) device. This will help analyzing the relationship between visible optical clearing and OCT devices resolution.

International audience; Background: The study proposes to improve bladder cancer diagnosis by (i) photodynamic diagnosis (PDD) using red-light excitation (632.8 nm) of 5-ALA induced-protoporphyrin IX in 9 patients’ bladder associated to the analysis of two types of signals to improve the diagnostic accuracy, and (ii) numerical modeling of scattering coefficient for providing biological explanations of the results obtained.Methods: Two modalities of the bladder cancer spectral diagnosis are presented: conventional PDD and intensity assessment of the diffusely reflected laser light by fiber-optic spectroscopy. Experiments are done in clinical conditions and as a series of numerical simulations.Results: High-grade cancerous bladder tissues display twice a higher relative fluorescence intensity (mean value 1, n = 9) than healthy (0.39, n = 9), dysplastic (0.44, n = 5) tissues and CIS (0.39, n = 2). The laser back-scattering signal allows to discriminate most effectively high-grade cancerous and dysplastic tissues from normal. Numerical modeling of diffuse reflectance spectra reveals that spectral behavior of the back-scattered light depends on both, nuclear size and nuclear density of tumoral cells.Conclusions: Unlike the fluorescence signal, where its value is higher in the case of pathological tissues, the tendency of the laser signal to, both, decrease or increase in comparison with the signal from normal urothelium, should be perceived as a sign towards the neoplasm. Numerical simulation reveals that such a double-analysis at a multiwavelength mode potentially may be used to provide diagnostic accuracy.

The use of optical clearing agents makes it possible to increase the probing depth of non-invasive optical diagnostic methods. However, the protective epidermal barrier of the skin prevents the penetration of hydrophilic immersion liquids into the deeper layers of the skin. The aim of this study is to improve the efficiency of skin optical clearing by increasing the permeability of the epidermis for polyethylene glycol with MW 300 (PEG-300) using different physical approaches. We present the results of a comparative analysis of optical immersion clearing of skin in laboratory rats in vivo with and without preliminary ablation of epidermis, fraction microablation and sonophoresis. Laser ablation and microablation has been implemented using a setup based on a pulsed erbium laser (λ= 2940 nm) with different hand-pieces. Sonophoresis has been applied during 2 min with the following parameters: 1 MHz, 2 W/cm2, continuous mode. As an optical clearing agent (OCA) polyethylene glycol (PEG-300) has been used. Basing on optical coherence tomography, we have estimated the attenuation coefficient in the process of optical clearing in two regions at depths of 50–170 µm and 150–400 µm. The results have shown that both surface ablation of skin in vivo lead to the local edema of the affected region that increases the scattering coefficient. However, the intense evaporation of water from the ablation zone facilitates the optical clearing at the expense of tissue dehydration, particularly in the upper layers. Besides, fractional ablation enhances the both rate and degree of optical clearing in upper dermis layers but not affects the deeper dermis. Sonophoresis provides the most effective penetration of OCA into deeper dermis. Time dependences of attenuation coefficient in two regions of dermis at the separate and combined laser and ultrasound impact on the epidermal permeability for PEG-300 have been obtained.

Optical methods in medicine are exploit the light propagation through the biological tissue, to non-invasively extract morphological and geometrical parameters of the tissue under investigation, from the detected light. However, because the transport of photons into biological tissues of interest is weakened due to losses caused by multiple light scattering, absorption and reflectance, the depth resolution and photon penetration depth of these optical methods still need to be improved. The optical properties of biological tissues can be controlled using special biocompatible hyperosmotic agents or Optical Clearing Agents (OCA). The latter might penetrate inside a tissue, interact with and modify its natural high-scattering formation through different ways and thus, increase the photons penetration within the biological tissue. The aim of this work was to study the modifications in depth resolution of the proposed Spatially Resolved Multi-Modal Spectroscopy (SRMMS) method by combining it with an optical clearing approach and to estimate the applicability of this method for future clinical use. As an OCA, PEG-400/DMSO (80%/20% vol/vol) and Sucrose/PEG-400/PG (50%/45%/5% vol/vol) solutions were used. Depending on the experimental condition, either one of 2 OCA, or saline solution or nothing ("dry" condition) was applied on the skin surface of 2-layer hybrid model, made of skin layer on top and the gel layer, containing exogenous fluorophore Chlorin e6, on bot. The SRMMS probe made of one central excitation fiber and 4 rings of collecting fibers for collecting spectroscopic data with the separation by depth, was placed in contact with the skin at the area of application. Then, Diffuse Reflectance and excited on a different wavelengths (365,385,395, 405 and 415 nm) Autofluorescence spectra were aquired at initial time point, and then every 4 minutes within 36 minutes. Aquired DR and AF spectra were preprocessed, and the Area Under the Curve (AUC) values were calculated for the specific wavelength bandwidths of interest for the skin-AF and Ce6-fluorescence spectra obtained at every of the 5 excitation peaks. AUC values were normalized to the T0 respective values to get the time kinetics curves of the spectroscopic signals. Time kinetics of skin-AF and Ce6-fluorescence spectrum AUC showed that under 36 minutes of OCA application it is possible to observe certain enhanced light penetration effect through an increasing of normalized Ce6 AUC kinetics and a decreasing of normalized AF AUC kinetics. Thus, it was possible to observe that optical clearing led to increased depth resolution with time. Moreover, the effect of clearing itself was observed to be dependent on the chosen OCA, while the saline solution application didn’t cause significant changes in normalized fluorescence intensities. The result of “dry” condition experiment highlighted that while there were no significant changes in AF spectrum amplitudes, a strong increase of Ce6 fluorescence emission intensity was collected from the bottom gel layer. This is probably due to drying of an ex vivo skin sample and the applied probe pressure effect.

We present a comprehensive analysis of the submissions to the first edition of the Endoscopy Artefact Detection challenge (EAD). Using crowd-sourcing, this initiative is a step towards understanding the limitations of existing state-of-the-art computer vision methods applied to endoscopy and promoting the development of new approaches suitable for clinical translation. Endoscopy is a routine imaging technique for the detection, diagnosis and treatment of diseases in hollow-organs; the esophagus, stomach, colon, uterus and the bladder. However the nature of these organs prevent imaged tissues to be free of imaging artefacts such as bubbles, pixel saturation, organ specularity and debris, all of which pose substantial challenges for any quantitative analysis. Consequently, the potential for improved clinical outcomes through quantitative assessment of abnormal mucosal surface observed in endoscopy videos is presently not realized accurately. The EAD challenge promotes awareness of and addresses this key bottleneck problem by investigating methods that can accurately classify, localize and segment artefacts in endoscopy frames as critical prerequisite tasks. Using a diverse curated multi-institutional, multi-modality, multi-organ dataset of video frames, the accuracy and performance of 23 algorithms were objectively ranked for artefact detection and segmentation. The ability of methods to generalize to unseen datasets was also evaluated. The best performing methods (top 15%) propose deep learning strategies to reconcile variabilities in artefact appearance with respect to size, modality, occurrence and organ type. However, no single method outperformed across all tasks. Detailed analyses reveal the shortcomings of current training strategies and highlight the need for developing new optimal metrics to accurately quantify the clinical applicability of methods.

International audience; We propose a method to generate beams according to transmission limitation condition by using the multi-distance phase retrieval algorithm. Propagation properties of hollow beams were determined by several intensity patterns along the travel axis. Predicted beams were obtained using a two-step phase filtering from a Gaussian beam with fundamental mode. An iterative phase retrieval method was employed for calculating the phase distribution in the filtering mask. This beam generation approach matched special propagation characteristics of the beams in practical applications.

International audience; An enhanced optical single-channel asymmetric cryptosystem for color image is proposed by using hyperchaotic system and random modulus decomposition (RMD) in gyrator domains. For increasing the security of the encryption scheme, a novel 4D four-winged hyperchaotic system is utilized to generate several hyperchaotic phases in the encryption approach. Subsequently, the RMD is implemented to obtain the effective trapdoor one-way function in the asymmetric process. Finally, a scrambling encoding algorithm is designed to combine and randomize the intermediate and hyperchaotic data, and the result can be regarded as the ciphertext and private key of the cryptosystem. In the decryption approach, the ciphertext and private key are imported into the input plane of gyrator transform. In fact, the proposed cryptosystem is also applicable in information authentication since the hyperchaotic data is prerequisite both in encryption and decryption approaches. Various numerical simulations are made to demonstrate the validity and capability of the proposed cryptosystem.

International audience; In coherent diffraction imaging (CDI) systems, the results of phase retrieval could be deteriorated by the inevitable experimental noise. To address the problem, a noise-robust algorithm is designed with weighted feedback and adjustable frequency filtering. The frequency filter serves as the smoothness constraint and has an adaptive parameter during iterations, to suppress the noise as well as avoid the convergence stagnancy of iterative phase retrieval. Numerical simulations and experimental results demonstrate that the proposed algorithm is superior in reconstruction quality under noisy conditions and increases the convergence speed. Furthermore, the minimum acceptable number of measurements of diffracting images is reduced. This work is beneficial to data synthesis in CDI systems.

The security is a significant topic in transmission and management of pictures, while encryption is an effective method for protecting the secret images. In recent years, the chaotic/hyperchaotic system has been thoroughly developed in image encryption area due to its high randomness. In this chapter, the optical cryptosystems based on chaotic/hyperchaotic system are expressed in detail. We starts with the brief introduction of various chaotic/hyperchaotic systems, then several optical cryptosystems based on the chaotic/hyperchaotic map are expressed in detail. Some experiments are made to verify the security and robustness of these schemes.

International audience; We present an optical hyperspectral image cryptosystem using improved Chirikov mapping in the gyrator transform domains. This optical encryption scheme can hide the spatial and spectrum information simultaneously. First, the original hyperspectral image is converted into binary format and then extended into a one dimensional array. Subsequently, improved Chirikov mapping is performed to generate a position array. Here, the binary array of the image can be scrambled by the position sequence. Finally, three thin cylinder lenses are controlled using a PC to implement the gyrator transform, and the amplitude and phase information in the output plane is considered to be the encrypted information. Some numerical simulations verify the validity and capability of the proposed cryptosystem