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In the framework of the depth detection of tumor using the diffusion equation, a finite element method is proposed in order to solve the time-dependent light propagation in highly scattering media. A tumor-like object is positioned in the media. The finite element method tacks into account Robin type air-tissue boundary conditions. This study is devoted to the depth localization of a tumor enclosed into a breast tissue-like slab. Cartesian coordinates are used in order to solve the time-dependent diffusion approximation. A short laser pulse of 1ps is considered. The transillumination technique is able to laterally detect the objects when the source and detector are moved together on the same axis. In order to perform the depth localization of the inclusion, we were interested in a non-coaxial transillumination technique conjugated to interesting contrast functions based on the mean time of flight of photons. These functions allow to localize axially the inclusion using the high scattering processes. Thus, we performed first results of a depth indicator of a tumor. We now perform a parametric study. The optical properties of the slab are varying. Furthermore, different sizes of the objects are tested. Thus, the influence and the variation of these parameters on the depth indicator are shown. Our study demonstrates the possibility to deeply localize a tumor enclosed in a breast tissue using the high scattering processes induced by a tumor. To enhance the scattering processes, an interesting way is then to use recent nanoparticles allowing to modify the scattering coefficient.

The goal of the present work is to analyse multiple scattering in laser Doppler blood flowmetry reactive hyperaemia experiments. For this purpose, three different kinds of outputs from a laser Doppler flowmeter are studied: the concentration of moving blood cells (CMBC), the linearised unfiltered flux and the unlinerised unfiltered flux. Three vascular occlusion lengths of time are observed on eight healthy volunteers. For each reactive hyperaemia experiment, the difference between the linearised unfiltered flux and the unlinearised unfiltered flux is calculated to examine the multiple scattering. The latter is considered as a function of time and compared to blood flux and concentration of erthrocyte variations. This work shows that, during reactive hyperaemia, the multiple scattering is predominant when the CMBC signal reaches its peak, the latter occurring at the peak of perfusion. However, very rapidly the multiple scattering becomes negligible whereas the CMBC and the linearised flux still take high values. Moreover, the longer the occlusion length of time, the longer the presence of the multiple scattering.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Breast tissues can be investigated by means of the frequency- resolved spectroscopy, using the transmittance data. A model based on the Fourier transform of the time-resolved transmittance is firstly established, by considering the slightly compressed breast tissues as a finite homogeneous slab of different thicknesses. Two methods of determining the optical properties of this arrangement are presented. The former allows to use moderate modulation frequency of about 100 MHz, while the second requires a limited frequency range of 10 - 20 MHz, in accordance with the low frequency approximation. Under these conditions, computations reveal the potential of extracting the main optical tissue properties from the recorded phase angle shift and modulation linked to transmittance data, at fixed operating modulation frequency. In each case, graphical or numerical solutions can provide good estimates of both reduced scattering and absorption coefficients.

The purpose of this work was to gain better overall picture to the thermal process involved in ablation of biological media performed by means of both continuous waves (cw) and pulsed laser irradiations. The theoretical analysis is based upon a computerized laser evaporative model. This scheme has been applied in order to clarify the following situations: (1) Ablation of tissue assimilated as water with finite absorption coefficient. (2) Tissue ablation by cw argon laser using gel (tissue-like phantom material) as a model system for tissue. (3) Skin ablation performed by pulsed Er:YAG laser radiation. In each case the role played by optical absorption in the dynamics of the ablation process is depicted. Typically, it appears that the position of the ablation front (or crater depth) and the transient ablation velocity are both influenced by tissue absorption while the steady-state stays independent on this parameter and evolves linearly with power density. Additionally, the ablation temperature beyond the moving front can reach a maximum higher than ablation threshold temperature. The peak temperature and its location are mediated by tissue type. Calculations show that for small absorption coefficients higher temperatures are reached at deeper levels. In contrast, at fixed absorption coefficient, the growing of the power density increases the peak temperature but reduces the penetration depth of the heated volume. The whole of computed data confirms that thermal laser ablation of tissue can be described as an explosive event and that a decrease of water content in the target alters the penetration depth which control the ablation rate.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.