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The research results contained in this dissertation relate to the novel field of engineered tissue optics. Biological tissue such as skin is highly opaque due to multiple light scattering. However, it has been shown that certain hyper-osmotic chemicals can temporarily render turbid tissues such as skin optically transparent by reducing light scattering. The mechanisms involved in this process are believed to be a combination of dehydration and index matching. In order to capitalize on the non-invasive nature of light-tissue interactions for diagnostic and therapeutic purposes, hyper-osmotic optical clearing agents need to be delivered transepidermally. The first part of this dissertation is devoted to investigation of different methods to temporarily reduce the natural skin barrier posed by the stratum corneum in order to allow topically applied optical clearing agents to diffuse into epidermis and dermis. Methods such as needle-free injection gun, micro-needles, Er:YAG surface ablation, use of a 980 nm diode laser and mild surface abrasion using sandpaper were investigated. The second part of this dissertation investigated the effects of optical tissue clearing on tissue structure and influence on blood flow. Various imaging modalities such as optical coherence tomography (OCT), microscopy, confocal microscopy as well as transmission electron microscopy were employed to deduce how tissue structural changes can explain the temporary reduction of light scattering. / text

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Orientador: Rickson Coelho Mesquita / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-30T22:43:33Z (GMT). No. of bitstreams: 1 QuirogaSoto_AndresFabian_M.pdf: 7858431 bytes, checksum: cab3b799ea039aaac9d7d8039a9590ed (MD5) Previous issue date: 2016 / Resumo: A espectroscopia óptica de difusão DOS é uma técnica que usa luz no regime do infravermelho próximo (NIR) para extração de informações fisiológicas em tecidos biológicos de forma não invasiva, tais como as concentrações de oxi-hemoglobina (HbO) , desoxi-hemoglobina (Hb) e a saturação de oxigênio no tecido (StO_2). Esta técnica baseia-se no fato de que a luz do infravermelho próximo se propaga difusivamente no tecido biológico, conseguindo se aprofundar alguns centímetros e voltar na superfície de incidência, e sofrendo alterações ao atravessar o meio devido à absorção e ao espalhamento do tecido. Este enfoque utiliza a equação de difusão para o modelamento da luz e suas soluções para conseguir as propriedades ópticas absolutas, que permite inferir as informações fisiológicas do tecido. A técnica experimental DOS utiliza fontes que emitem pulsos ultracurtos (Time Domain DOS) ou intensidades moduladas (Frequency Domain DOS) para extrair tais informações. No entanto, a implementação destas técnicas requerem uma eletrônica avançada, tornando a construção complicada ou a aquisição custosa. Por outro lado, os equipamentos que usam fontes contínuas medem apenas variações relativas dos coeficientes de absorção do tecido. Neste trabalho, estudou-se uma nova metodologia a partir da espectroscopia óptica de difusão usando fontes de onda contínua para vários comprimentos de ondas (CW-DOS) a fim de extrair os valores absolutos de absorção e espalhamento do tecido. A metodologia foi validada com dados ópticos em phantoms e camundongos, conseguindo inferir as propriedades ópticas absolutas para cada estágio. Os resultados refletem que a metodologia é uma boa alternativa para extração de informação fisiológica de forma simples e confiável, e que serve como base para a construção de novos equipamentos de DOS / Abstract: Diffuse Optical Spectroscopy (DOS) is a technique that employs near infrared (NIR) light to noninvasively extract physiological information from biological tissue, such as microvascular oxy-hemoglobin (HbO) and deoxy-hemoglobin (Hb) concentrations, and tissue oxygen saturation (StO_2). DOS is based on the fact that NIR light diffuses through deep tissue and interacts with tissue cells and molecules before returning to the surface. Therefore, the tissue composition can be estimated by the absorption and scattering coefficients, which can be monitored by the intensity detected of scattered light. DOS uses the diffusion equation for modeling light propagation, and its solutions to estimate the absolute optical properties. Typical experimental methods in DOS employ ultrashort-pulsed light sources (Time Domain DOS) or intensity modulated light sources (Frequency Domain DOS) to extract such information. However, the implementation of these techniques requires advanced electronics, which makes its use complicated and/or expensive. Instruments that use continuous-wave (CW- DOS) light sources are limited to estimate relative changes of the absorption coefficient, only. In this dissertation, we analyze a methodology based on continuous-wave diffuse optical spectroscopy with several wavelengths to estimate the absolute values of absorption and scattering coefficients of biological tissue. The methodology was validated in optical phantoms and in mice. Our results suggest that the methodology can be a good approach for estimating physiological information in a simple and reliable way, and it can be used as the basis for the construction of new DOS equipments / Mestrado / Física / Mestre em Física / 1373920/2014 / CAPES

Indiana University-Purdue University Indianapolis (IUPUI) / Photoacoustic Imaging is a non-invasive optical imaging modality used to image biological tissues. In this method, a pulsating laser illuminates a region of tissues to be imaged, which then generates an acoustic wave due to thermal volume expansion. This wave is then sensed using an acoustic sensor such as a piezoelectric transducer and the resultant signal is converted into an imaging using the back projection algorithm. Since different types of tissues have different photo-acoustic properties, this imaging modality can be used for imaging different types of tissues and bodily organ systems. This study aims at quantifying the process of light conversion into the acoustic signal. Light travels through tissues and gets attenuated (scattered or absorbed) or reflected depending on the optical properties of the tissues. The process of light propagation through tissues is studied using Monte Carlo simulation software which predicts the propagation of light through tissues of various shapes and with different optical properties. This simulation gives the resultant energy distribution due to light absorption and scattering on a voxel by voxel basis. The Monte Carlo code alone is not sufficient to validate the photon propagation. The success of the Monte Carlo code depends on accurate prediction of the optical properties of the tissues. It also depends on accurately depicting tissue boundaries and thus the resolution of the imaging space. Hence, a validation algorithm has been designed so as to recover the optical properties of the tissues which are imaged and to successfully validate the simulation results. The accuracy of the validation code is studied for various optical properties and boundary conditions. The results are then compared and validated with real time images obtained from the photoacoustic scanner. The various parameters for the successful validation of Monte Carlo method are studied and presented. This study is then validated using the algorithm to study the conversion of light to sound. Thus it is a significant step in the quantification of the photoacoustic effect so as to accurately predict tissue properties.