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.
The estimation of skin optical properties by means of inverse problem solving from spatially resolved diffuse reflectance (SR-DR) spectra is one way to exploit the acquired clinical signals. This method requires the comparison between the experimental spectra collected with a medical device, and spectra generated by the photons transport numerical simulations. This comparison is usually limited to spectral shape due to the absence of intensity standardization of the experimental DR spectra. This study proposes to theoretically (using photometric calculation) and experimentally (from experimental spectra acquired on optical phantom) establish a corrective factor to obtain common intensity unit for experimental and simulated signals.
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.
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