Irene Salas-García

Superficial radially resolved fluorescence and 3D photochemical time-dependent model for photodynamic therapy

Photodynamic therapy (PDT) dosimetric tools are crucial for treatment planning and noninvasive monitoring by means of fluorescence. Present approaches consider usually a 1D problem, a simple photochemical process, or a spatially homogeneous photosensitizer. In this work, a radially resolved superficial photosensitizer fluorescence and 3D photochemical time-dependent PDT model are presented. The model provides a time-dependent estimation of tissue fluorescence and the photosensitizer and singlet oxygen 3D concentrations. The model is applied to a basal cell carcinoma treated by Metvix topical photosensitizer protocol. The analysis shows the potentiality in treatment planning and monitoring. The fluorescence results are in agreement with previous measurements.

Photosensitizer absorption coefficient modeling and necrosis prediction during Photodynamic Therapy.

The development of accurate predictive models for Photodynamic Therapy (PDT) has emerged as a valuable tool to adjust the current therapy dosimetry to get an optimal treatment response, and definitely to establish new personal protocols. Several attempts have been made in this way, although the influence of the photosensitizer depletion on the optical parameters has not been taken into account so far. We present a first approach to predict the spatio-temporal variation of the photosensitizer absorption coefficient during PDT applied to dermatological diseases, taking into account the photobleaching of a topical photosensitizer. This permits us to obtain the photons density absorbed by the photosensitizer molecules as the treatment progresses and to determine necrosis maps to estimate the short term therapeutic effects in the target tissue. The model presented also takes into account an inhomogeneous initial photosensitizer distribution, light propagation in biological media and the evolution of the molecular concentrations of different components involved in the photochemical reactions. The obtained results allow to investigate how the photosensitizer depletion during the photochemical reactions affects light absorption by the photosensitizer molecules as the optical radiation propagates through the target tissue, and estimate the necrotic tumor area progression under different treatment conditions.

FDTD-based Transcranial Magnetic Stimulation model applied to specific neurodegenerative disorders

Non-invasive treatment of neurodegenerative diseases is particularly challenging in Western countries, where the population age is increasing. In this work, magnetic propagation in human head is modelled by Finite-Difference Time-Domain (FDTD) method, taking into account specific characteristics of Transcranial Magnetic Stimulation (TMS) in neurodegenerative diseases. It uses a realistic high-resolution three-dimensional human head mesh. The numerical method is applied to the analysis of magnetic radiation distribution in the brain using two realistic magnetic source models: a circular coil and a figure-8 coil commonly employed in TMS. The complete model was applied to the study of magnetic stimulation in Alzheimer and Parkinson Diseases (AD, PD). The results show the electrical field distribution when magnetic stimulation is supplied to those brain areas of specific interest for each particular disease. Thereby the current approach entails a high potential for the establishment of the current underdeveloped TMS dosimetry in its emerging application to AD and PD.

Comparative study of optical activity in chiral biological media by polar decomposition and differential Mueller matrices analysis

The introduction of polarimetry in optical imaging of biological tissues provides a powerful method to enhance contrast and specificity in the characterization of anisotropic biological tissues. Moreover, the fact that Mueller calculus can deal with partially polarized light and depolarizing media enables to analyze the strong effect of scattering in light propagation through biological tissues. The inherent heterogeneity of biological tissues causes that multiple effects are overlapped in a single measurement. Regarding polarimetry, anisotropic structures can simultaneously exhibit birefringence, diattenuation and depolarization. Lu-Chipman polar decomposition has been widely used in order to isolate the effects and quantify each of them. However, it entails a limitation: as long as the original Mueller matrix is decomposed into the product of three components, the result of the decomposition varies with the order. In this work, we propose a polarimetric analysis based on differential Mueller matrices. This analysis is not affected by the order in which the effects take place within the medium. We apply it to the study of optical activity in chiral and turbid biological media, in particular to a solution of glucose mixed with an aqueous suspension of polystyrene microspheres. The results obtained by Lu-Chipman polar decomposition and by differential Mueller matrices analysis are compared. It will be shown that the results obtained by the polarimetric analysis proposed in this work are in good agreement with those obtained by polar decomposition, with the advantage that differential Mueller matrices provide additional information to further develop polarimetric analysis in a robust way.

Polarized light Monte Carlo analysis of birefringence-induced depolarization in biological tissues

In this work we analyze the impact of linear birefringence on biological tissues depolarization, which is essential for correctly interpreting experimental results. Our approach is based on the polarized light Monte Carlo method in transmission. We present a comparative analysis of light depolarization in biological tissues with different values of linear birefringence and particle sizes, in order to evaluate its impact on the calculated parameters.

Maturity of human bone estimated by FTIR spectroscopy analysis: implications for ostheoporosis

This work studies the possible variations of the properties of mineral and organic bone components with regard to the anatomical position and the patients age. Autopsies of healthy human iliac crest have been analyzed within a wide range of ages (26-88), measuring different anatomical positions in trabecular bone by means of FT-IR spectroscopy. The study was focused on the analysis of ν1, ν3 phosphate, ν2 carbonate amida I and amida II bands. From the resulting spectra the cristallinity/maturity index, the collagen cross-links ratio and the carbonate/phosphate ratio were calculated. All of them provide information of bone mineral and collagen maturity. The results show a trend in the spatial distribution of mineral and collagen maturity in most of the samples. The most mature mineral and collagen of the bone were found to be located in the trabecular center, while the youngest were situated in the peripheral regions. However, this behavior has exceptions that seem to be related with the patients age.

Predictive Analysis of Photoacoustic Tomography Images in Dermatological Liposarcoma

Photoacoustic Tomography is a novel and promising imaging technique for tissue diagnosis. It employs an optical radiation for tissue irradiation, and detects the generated acoustic waves. By means of this approach it is capable of obtaining high resolution images at depths beyond the limits of purely optical techniques. The study of the potential efficiency of these techniques for diagnosis requires a predictive model for photoacoustic images. In this work we present a predictive complex model for Photoacoustic Tomography images. The model implements optical propagation by means of a Monte Carlo approach, initial pressure distribution and image reconstruction by the k-space method. We apply the method to dermatological liposarcoma at several states, and evaluate the validity of the images for diagnosis.

Comparison and evaluation of the laser beam-shaping techniques

Over the past several decades, free-space optical (FSO) systems have gained a specific place in the wireless technology area. The application of these systems is advantageous for high bandwidths, a license free band and quick installation. The main drawback of FSO systems is their dependence on the state of the atmosphere causing deterioration of the FSO systems availability. One of the atmospheric effects which has an essential impact on the performance of the FSO systems is atmospheric turbulence. Atmospheric turbulence leads to fluctuation of the optical intensity in the plane of the receiving aperture. It has been shown that to reduce the effect of atmospheric turbulence, uniform distribution of the optical intensity within the cross section of the beam in the plane of transmitting aperture (phenomenon of diffraction is neglected) and a suffciently large diameter of the circularly symmetric receiving aperture (to achieve aperture averaging effect) are needed. The main idea of our paper is the problem of beam shaping at the transmitter. In our contribution the technique of transformation of a Gaussian beam into a beam with uniform distribution of optical intensity is discussed. For the mentioned transformation we experimentally tested several shaping methods such as multi aperture beam integrators, diffractive diffusers, etc. Usage of laser sources with different degrees of coherence was considered. The purpose of these techniques is to create an optical beam with uniform distribution of optical intensity on the transmitter output. In order to compare and evaluate the particular shaping techniques, a new Trans- formation Complex Quality (TCQ) parameter was defined. The TCQ parameter indicates the optimal shaping technique and also evaluates the quality of the resulting transformed beam with respect to its resistance towards atmospheric turbulence.

Detection of non-standard atmospheric effects in FSO systems

Modern free-space optical (FSO) communication systems in many aspects overcome wire or radio communications. They offer a license-free operation and a large bandwidth. Operation of outdoor FSO links struggles with many atmospheric phenomena that deteriorate phase and amplitude of the transmitted optical beam. Thanks to the recent advancing development, these effects are more or less well understood and described. Goal driven research increased the link availability. Besides increasing the availability of data links it is necessary to focus on the accuracy and reliability of testing optical links. Research of the data optical links is focused on the transmission of a large amount of data whereas the testing FSO link is designed to achieve maximal resolution and sensitivity thus improving accuracy and repeatability of the atmospheric effects measurement. Given the fact that testing links are located in the measured media, they are themselves influenced by it. Phenomena such as the condensation on transceiver windows (rain, frost) and the deviation of the optical beam path caused by the wind are referred to as non-standard effects. Non-standard effects never occur independently; therefore we must always verify the cross-sensitivity of the testing link. In the paper we respond to an increasing number of articles dealing with influence of the atmosphere on the link but ignoring the cross-sensitivity of the testing link on other variables than tested. In conclusion, we carry out qualitative and quantitative analysis of self-identified non-standard effects.

Comparative Numerical Analysis of Magnetic and Optical Radiation Propagation in Adult Human Head

In this work, magnetic and optical propagation in human head are modeled by FDTD and Monte Carlo methods. Both of them use a realistic high-resolution three-dimensional human head mesh. The numerical methods are applied to the analysis of magnetic and optical radiation distribution in the brain using different sources. The results show the characteristics of both types of stimulation, and highlight the spatial selectivity achieved by optical sources, which entails a high potential for illuminating specific brain regions. The presented approach can be applied for predictive purposes in magnetic stimulation techniques and in the emerging field of optical brain stimulation.