Approche fréquentielle pour l'identification in vivo de paramètres thermiques

In order to determine the risks of invalidating burns and to optimize the protection of individuals subjected to a laser attack, the development of a mathematical model is required. This predictive tool aims to estimate the evolution of temperature in the three cutaneous layers of skin. In such a context, the determination of key parameters governing the heat transfers is essential. A major difficulty lies in the fact that the thermal diffusivities of each layer of the human skin are not accurately known. The required in vivo identification of such parameters provides numerous constraints to avoid tissue trauma. The periodic methods are therefore particularly adapted. Such methods allow to obtain a set of relevant information by providing measurements which only slightly heat the cutaneous layers

Identification paramétrique d'un multicouche biologique par méthode périodique en réflexion

Afin de déterminer les risques de brûlures invalidantes et d\u27optimiser les dispositifs de protection de l\u27individu soumis à une agression laser, il est nécessaire de développer un modèle mathématique. Cet outil prédictif doit permettre d\u27estimer l\u27élévation de température dans les couches cutanées. Dans un tel contexte, la détermination des paramètres clés régissant les transferts thermiques est une étape essentielle. Une difficulté majeure réside en ce que les diffusivités thermiques de l\u27épiderme et du derme sont mal connues. L\u27identification in vivo de ces paramètres impose de nombreuses contraintes afin d\u27éviter tout traumatisme dans les tissus. Les méthodes périodiques sont alors particulièrement adaptées car elles permettent d\u27obtenir un ensemble d\u27informations pertinentes par des mesures non intrusives en réflexion qui ne sollicitent que faiblement les couches cutanées

Skin burns after laser exposure: Histological analysis and predictive simulation

Thermal effects of laser irradiation on skin are investigated in this paper. The main purpose is to determine the damage level induced by a laser exposure. Potential burns induced by two lasers (wavelength 808 nm and 1940 nm) are studied and animal experimentations are performed. Several exposure durations and laser powers are tested. Based on previous works, a mathematical model dedicated to temperature prediction is proposed and finite-element method is implemented. This numerical predictive tool based on the bioheat equation takes into account heat losses due to the convection on skin surface, blood circulatory and also evaporation. Thermal behavior of each skin layer is also described considering distinct thermal and optical properties. Since the mathematical model is able to estimate damage levels, histological analyses were also carried through. It is confirmed that the mathematical model is an efficient predictive tool for estimation of damage caused by lasers and that thermal effects sharply depend on laser wavelength

Development of a skin burn predictive model adapted to laser irradiation

Laser technology is increasingly used, and it is crucial for both safety and medical reasons that the impact of laser irradiation on human skin can be accurately predicted. This study is mainly focused on laser–skin interactions and potential lesions (burns). A mathematical model dedicated to heat transfers in skin exposed to infrared laser radiations has been developed. The model is validated by studying heat transfers in human skin and simultaneously performing experimentations an animal model (pig). For all experimental tests, pig’s skin surface temperature is recorded. Three laser wavelengths have been tested: 808 nm, 1940 nm and 10 600 nm. The first is a diode laser producing radiation absorbed deep within the skin. The second wavelength has a more superficial effect. For the third wavelength, skin is an opaque material. The validity of the developed models is verified by comparison with experimental results (in vivo tests) and the results of previous studies reported in the literature. The comparison shows that the models accurately predict the burn degree caused by laser radiation over a wide range of conditions. The results show that the important parameter for burn prediction is the extinction coefficient. For the 1940 nm wavelength especially, significant differences between modeling results and literature have been observed, mainly due to this coefficient’s value. This new model can be used as a predictive tool in order to estimate the amount of injury induced by several types (couple power-time) of laser aggressions on the arm, the face and on the palm of the hand

Evaluation du risque de brûlure par exposition à des rayonnements lasers. Expérimentations et modélisation.

La technologie laser étant de plus en plus utilisée, l\u27objectif de cette étude est de déterminer quel type d\u27agression laser entraîne quel dégât (brûlure) sur la peau. Il existe en effet unedifférence de diagnostic et de pronostic des lésions en fonction de la longueur d’onde du laser utilisé. Pour ce faire, des expérimentations in vivo sur modèle animal ont été menées à l\u27aide de trois lasers émettant respectivement à 808 nm, 1,94 μm et 10,6 μm. Parallèlement, un modèle mathématique permettant de simuler l\u27effet thermique d\u27une agression laser sur la peau a été développé

Givry. A constraint optimization framework for mapping a digital signal processing application onto a parallel architecture

onto a Parallel Architectur