Kidney stones are a global problem that cause physical pain and may lead to chronic kidney disease. Recent statistics indicate the incidence of kidney stones is increasing worldwide, and usually varies from 2 to 20% depending on countries1 and especially on diabetes or obesity incidence in such countries. Intra-operative (i.e. in vivo) characterization of kidney stones is at stake for a better diagnostic management of patients. Such a goal could be achieved by optical methods. The current study aims at evaluating if absorption and scattering coefficients measurements combined to automatic classification based on machine-learning methods could be of interest in assisting urologists with kidney stones characterization. Absorption and scattering coefficients were measured using the inverse adding doubling method (IAD). This method based on solving inverse problem takes as input data measurements acquired on a double integrating spheres optical bench developed in the CRAN laboratory. The dataset is made of absorption and scattering coefficients measured every 10 nm from 535 to 845 nm on 16 kidney stones: 4 kidney stones in each diagnostic class under consideration (1a, 3a, 4c and 5a). Class 3a (5a respectively) kidney stones display the highest (lowest resp.) absorption and scattering coefficients: 3 and 30 mm-1 (1 and 10 mm-1 respectively) at 650 nm. Support-vector machine (SVM) and k-nearest neighbors (k-NN) methods were used to perform automatic classification: k-NN reached 98%-accuracy in the four-class confusion matrix when considering both absorption and scattering coefficients. Although a high intra-class variability was observed and may be seen as the main limitation of the study, this good classification rate is worth taking into account to keep on investigating this method on more kidney stones per class as a potential tool for diagnostic assistance for urologists.
Whether for diagnosis, therapy or surgery, the estimation of optical properties (OP) of biological tissues is now of interest in the medical context. Indeed, optical methods are increasingly used in modern medicine, and these require knowledge of the behavior of light within the tissue. The presentation contribution aims to validate the estimation process of absorption and scattering coefficients values obtained using spatially-resolved diffuse reflectance (SR-DR) spectroscopy by comparing the obtained results with those of the reference double integrating spheres (DIS) technique. A set of nine optical phantoms based on methylene blue and intralipids allowing to tune absorption and scattering properties was prepared, from which diffuse reflectance spectra and integrating spheres measurements were acquired respectively. Work presented here reports both estimations approaches developed and highlights the relative spreads of optical properties between DR, DIS and theoretical values (i.e. according scatterer and absorber concentrations introduced in phantoms). This validation on optical bench will allow to later estimate the OP from in-vivo DR spectra acquired on skin samples, to assist the surgeon in non-invasively diagnosing the health status of a tissue around a skin carcinoma
In the context of optical biopsy for the diagnosis of skin carcinoma, spatially resolved diffuse reflectance (SR-DR) spectroscopy is widely used to discern healthy from lesional tissues. The estimation of diagnostically relevant optical properties by means of inverse problem solving is one way to exploit the acquired clinical spectra. This method requires the comparison between the latter spectra collected with a medical device (MD), and the ones generated by the photons transport numerical simulations. However, this comparison is typically limited to shape comparison (spectra are normalized before a term-by-term comparison) due to non-standardization of the experimental DR spectra, for which magnitude depends on the multifiber optics probe geometry and on a preliminary calibration measurement performed on a spectralon DR standard illuminated at a given distance. This study proposes to establish a corrective factor to overcome this dependence, and thus obtain clinical spectra whose intensity unit is identical to the simulated ones, i.e., the ratio between photons sent by the emitting fiber and captured by the collecting fibers. The photometric calculations leading to a theoretical value of this factor for various calibration measurement geometries are presented. Experimental validations performed on optical phantoms (with optical properties confirmed from double integrating sphere measurements) using an existing SR-DR MD reveal encouraging fitting between experimental and simulated calculation of such corrective factor. Those results highlight the interest of the method for the standardization of clinically acquired DR spectra i.e. their comparison in terms of absolute magnitudes.
Spatially resolved diffuse reflectance spectroscopy (SR-DRS) is a widely studied optical biopsy technique to investigate and to diagnose skin tissue modifications due to pathologies such as cancers. One way to exploit clinical spectra acquired with a SR-DRS medical device consists in estimating diagnostically relevant skin optical properties that is, by solving an inverse problem based on numerical simulations to generate spectra in accordance with the technical and geometrical features of the latter device. For realistic multi-layer skin media, the simultaneous estimation of layer-wise optical properties of interest is quite challenging (difficulty of convergence or non-unicity of the solution) and time consuming, especially for one or several parameters to be estimated in more than three layers of a skin model. To tackle this problem, the work presented here proposes an improved inverse problem solving scheme, which (i) sequentially determines the parameters of interest, layer by layer, in a 5-layer skin model using (ii) a custom cost-function adapted to the layered structure of the skin, i.e. considering wavelength and source-detector distance sensitivity to each layer. In-silico validation of the proposed approach was performed through convergence analysis towards ground truth simulated spectra. Using this sequential approach, the values of a 4-parameters vector were estimated with a relative errors of a few percent only and three times faster compared to current optimization method. Moreover, it brings morphological and physiological dimension to the inverse problem solving.
KEYWORDS: Spectroscopes, In vivo imaging, Skin, Tissues, Tissue optics, Scattering, Photodetectors, Monte Carlo methods, Inverse optics, Diffuse reflectance spectroscopy
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.
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.
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