Deep skin homogeneity and light diffusion: An accelerated Monte Carlo model for in vivo skin characterization and consumer perception.

The appearance of healthy and youthful skin is related to many factors of the skin optical properties as perceived by our visual sense. The optics of light travelling through human tissues has been extensively investigated in the field of biomedical applications, including the experimental characterization and modelling of skin optics and the propagation of light such as lasers through the layers. This work presents an innovative approach to probe deep skin by means of spectrally and spatially resolved light diffusion in the different layers of skin. Dual hyperspectral measurements of the panellist's skin are performed in vivo on subjects to obtain reflectance and light diffusion spectra. Both are simultaneously fitted by a GPU-accelerated Monte Carlo model to obtain skin optical parameters as a function of depth. The results show a clear correlation between deep skin light diffusion at wavelengths above 590 nm and the subject age, which indicates a progressive degradation of skin homogeneity with age. The effect of this orange-red light diffusion background is to alter the colour tone of the skin. A skincare product is used to show that the warmer skin colour tone is clearly perceivable to consumers when evaluating facial images with and without the product. The product effect also correlates well with hyperspectral measurements. Lastly, this innovative approach demonstrates a first step in real-time skin characterization for consumers and opens the door to customized cosmetic solutions for individual needs.

L'aspect jeune et en bonne santé de la peau est lié à de nombreux facteurs des propriétés de la peau perçues par notre sens visuel. L'optique de la lumière qui traverse les tissus humains a fait l'objet de recherches approfondies dans le domaine des applications biomédicales, notamment la caractérisation expérimentale, la modélisation de l'optique cutanée et la propagation de la lumière telle que les lasers à travers ses couches. Ce travail présente une approche innovante permettant de sonder la peau profonde au moyen d'une diffusion de la lumière résolue spectralement et spatialement dans les différentes couches de la peau. Des mesures hyperspectrales doubles de la peau du panéliste sont effectuées in vivo sur des sujets pour obtenir des spectres de réflectance et de diffusion de la lumière. Les deux sont simultanément ajustés par un modèle Monte Carlo accéléré par processeur graphique afin d'obtenir les paramètres optiques de la peau comme fonction de sa profondeur. Les résultats montrent une corrélation claire entre la diffusion de la lumière de la peau profonde à des longueurs d'onde supérieures à 590 nm et l'âge du sujet, ce qui indique une dégradation progressive de l'homogénéité de la peau avec l'âge. L'effet de ce fond de diffusion de la lumière rouge­orangée est l'altération de la couleur de la peau. Un produit de soin de la peau a été utilisé pour montrer que le teint plus chaud de la peau était clairement perceptible par les consommateurs évaluant des images du visage avec ou sans produit. L'effet du produit est aussi bien corrélé avec les mesures hyperspectrales. Cette approche innovante démontre enfin une première étape dans la caractérisation de la peau en temps réel pour les consommateurs et ouvre la voie à une solution cosmétique personnalisée selon les besoins individuels.

Review of Advances in the Measurement of Skin Hydration Based on Sensing of Optical and Electrical Tissue Properties.

The presence of water in the skin is crucial for maintaining the properties and functions of the skin, in particular its outermost layer, known as the stratum corneum, which consists of a lipid barrier. External exposures can affect the skin's hydration levels and in turn, alter its mechanical and physical properties. Monitoring these alterations in the skin's water content can be applicable in clinical, cosmetic, athletic and personal settings. Many techniques measuring this parameter have been investigated, with electrical-based methods currently being widely used in commercial devices. Furthermore, the exploration of optical techniques to measure hydration is growing due to the outcomes observed through the penetration of light at differing levels. This paper comprehensively reviews such measurement techniques, focusing on recent experimental studies and state-of-the-art devices.

Digital imaging biomarkers feed machine learning for melanoma screening.

We developed an automated approach for generating quantitative image analysis metrics (imaging biomarkers) that are then analysed with a set of 13 machine learning algorithms to generate an overall risk score that is called a Q-score. These methods were applied to a set of 120 "difficult" dermoscopy images of dysplastic nevi and melanomas that were subsequently excised/classified. This approach yielded 98% sensitivity and 36% specificity for melanoma detection, approaching sensitivity/specificity of expert lesion evaluation. Importantly, we found strong spectral dependence of many imaging biomarkers in blue or red colour channels, suggesting the need to optimize spectral evaluation of pigmented lesions.

The optical properties of mouse skin in the visible and near infrared spectral regions.

Visible and near-infrared radiation is now widely employed in health science and technology. Pre-clinical trials are still essential to allow appropriate translation of optical methods into clinical practice. Our results stress the importance of considering the mouse strain and gender when planning pre-clinical experiments that depend on light-skin interactions. Here, we evaluated the optical properties of depilated albino and pigmented mouse skin using reproducible methods to determine parameters that have wide applicability in biomedical optics. Light penetration depth (δ), absorption (µa), reduced scattering (µ's) and reduced attenuation (µ't) coefficients were calculated using the Kubelka-Munk model of photon transport and spectrophotometric measurements. Within a broad wavelength coverage (400-1400nm), the main optical tissue interactions of visible and near infrared radiation could be inferred. Histological analysis was performed to correlate the findings with tissue composition and structure. Disperse melanin granules present in depilated pigmented mouse skin were shown to be irrelevant for light absorption. Gender mostly affected optical properties in the visible range due to variations in blood and abundance of dense connective tissue. On the other hand, mouse strains could produce more variations in the hydration level of skin, leading to changes in absorption in the infrared spectral region. A spectral region of minimal light attenuation, commonly referred as the "optical window", was observed between 600 and 1350nm.