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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Application of polarization sensitive optical coherence tomography (PS-OCT) and phase sensitive optical coherence tomography (PhS-OCT) for retinal diagnostics

Paranjape, Amit Shrikant 22 June 2011 (has links)
An Enhanced Polarization-Sensitive Swept Source Optical Coherence Tomography (EPS-SS-OCT) instrument for high sensitivity cross-sectional imaging of Retinal Nerve Fiber Layer (RNFL) has been designed, constructed, and verified. The instrument is capable of measuring the thickness and birefringence of the RNFL. Birefringence change of the RNFL could serve as an early indicator of glaucoma. The associated image processing methods for completely automated, time efficient algorithm to segment the RNFL in images of the human retina recorded by the EPS-SS-OCT. Detected RNFL boundaries are used to compute peripapillary thickness maps. Numerical algorithms to compute the birefringence of the detected RNFL layer are presented along with the associated phase retardation and birefringence peripapillary maps. Glaucoma affects the vitality of retinal ganglion cell axons in the retinal nerve fiber layer (RNFL) and may be clinically detected through a change in RNFL birefringence. Comprehensive peripapillary maps of healthy and glaucoma suspect human RNFL birefringence were constructed using EPS-SS-OCT. Presence of macrophages is a hallmark of several retinal diseases such as drusen and age related macular degeneration. Application of photothermal Optical Coherence Tomography (OCT) to detect macrophages in ex vivo arteries which have engulfed nanoclusters of gold coated iron oxide (nanorose) is reported. Nanorose engulfed by macrophages in arteries absorb incident laser (800nm) energy and cause optical pathlength (OP) variation which is measured using photothermal OCT. OP variation in polydimethyl siloxane tissue phantoms containing varying concentrations of nanorose match values predicted from nanoparticle and material properties. Measurement of OP variation in arteries in response to laser excitation provides an estimate of nanorose concentration in arteries 2.5x109 particles/ml. OP variation in nanoparticle containing artery sections and tissue phantoms taking up nanorose has a different magnitude and profile from that observed in control aorta and phantoms without macrophages and is consistent with macrophage presence as identified with RAM-11 histology staining. Our results suggest that tissue regions with macrophages taking up nanorose can be detected using photothermal OCT. / text
42

Imaging Heterogeneous Objects Using Transport Theory and Newton's Method

Fredette, Nathaniel 2011 December 1900 (has links)
This thesis explores the inverse problem of optical tomography applied to two-dimensional heterogeneous domains. The neutral particle transport equation was used as the forward model to simulate how neutral particles stream through and interact within these heterogeneous domains. A constrained optimization technique that uses Newton's method served as the basis of the inverse problem. The capabilities and limitations of the presented method were explored through various two-dimensional domains. The major factors that influenced the ability of the optimization method to reconstruct the cross sections of these domains included the locations of the sources used to illuminate the domains, the number of separate experiments used in the reconstruction, the locations where measurements were collected, the optical thickness of the domain, the amount of signal noise and signal bias applied to the measurements, and the initial guess for the cross section distribution. All of these factors were explored for problems with and without scattering. Increasing the number of sources, measurements and experiments used in the reconstruction generally produced more successful reconstructions with less error. Using more sources, experiments and measurements also allowed for optically thicker domains to be reconstructed. The maximum optical thickness that could be reconstructed with this method was ten mean free paths for pure absorber domains and two mean free paths for domains with scattering. Applying signal noise and signal bias to the measured fluxes produced more error in the reconstructed image. Generally, Newton's method was more successful at reconstructing domains from an initial guess for the cross sections that was greater in magnitude than their true values than from an initial guess that was lower in magnitude.
43

Enhancement of contrast in optical coherence tomography : new modes, methods and technology

Adie, Steven G January 2007 (has links)
This thesis is concerned with exploiting the native optical coherence tomography (OCT) contrast mechanism in new ways and with a new contrast mechanism, in both cases to enhance the information content of the tomographic image. Through experiments in microsphere solutions, we show that static speckle contains information about local particle density when the effective number of scatterers in the OCT resolution volume is less than about five. This potentially provides contrast enhancement in OCT images based on local scatterer density, and we discuss the experimental conditions suited to utilising this in biological tissue. We also describe the corrupting effects of multiple scattering, a ubiquitous phenomenon in OCT, on the information content of the static speckle. Consequently, we detail the development of polarisation-based metrics for characterising multiple scattering in OCT images of solid biological tissues. We exploit a detection scheme used for polarisation-sensitive contrast for a new purpose. We present experiments demonstrating the behaviour of these metrics in liquid phantoms, and in biological tissues, ranging from homogeneous non-birefringent to highly heterogeneous and birefringent samples. We discuss the conditions under which these metrics could be used to characterise the relative contribution of single and multiple scattering and, thus, aid in the study of penetration depth limits in OCT. We present a study of a new contrast mechanism - dynamic elastography which seeks to determine the dynamic mechanical properties of tissues. We present a framework for describing the OCT signal in samples undergoing vibrations, and perform experiments at vibration frequencies in the order of tens to hundreds of Hertz, to confirm the theory, and demonstrate the modes of measurement possible with this technique. These modes of measurement, including acoustic amplitude-sweep and frequency-sweep, could provide new information about the local mechanical properties of a sample. We describe a technological advancement enabling, in principle, measurements of local tissue refractive index contrast much deeper within a sample, than is possible with conventional OCT imaging. The design is based on measurement of the optical path length through tissue filling a fixed-width channel situated at the tip of a needle. The needle design and calibration is presented, as well as measurements of scattering phantoms and various biological tissues. This design potentially enables the use of refractive index-based contrast enhancement in the guidance of breast biopsy procedures.
44

Ablação de pele queimada com laser de pulsos ultra-curtos para promoção da cicatrização. Avaliação por tomografia por coerência óptica, histologia, µATR-FTIR e microscopia não-linear / Ablation of burned skin with ultra-short pulses laser to promote healing. Evaluation by optical coherence tomography, histology, µATR-FTIR and Nonlinear Microscopy

SANTOS, MOISES O. dos 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:35:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
45

Espectroscopia de fluorescência na otimização da terapia fotodinâmica em carcinoma espinocelular de pele e sua avaliação utilizando tomografia por coerência óptica / Fluorescence spectroscopy in the optimization of photodynamic therapy of skin squamous cell carcinoma and its evaluation by optical coherence tomography

GOULART, VIVIANE P. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:33:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:05Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
46

Ablação de pele queimada com laser de pulsos ultra-curtos para promoção da cicatrização. Avaliação por tomografia por coerência óptica, histologia, µATR-FTIR e microscopia não-linear / Ablation of burned skin with ultra-short pulses laser to promote healing. Evaluation by optical coherence tomography, histology, µATR-FTIR and Nonlinear Microscopy

SANTOS, MOISES O. dos 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:35:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:00Z (GMT). No. of bitstreams: 0 / As queimaduras causam alterações na estrutura anatômica da pele associadas a trauma. As queimaduras podem ser classificadas em lesões de primeiro, segundo e terceiro grau. As queimaduras de terceiro grau têm sido grande foco de pesquisas em busca de tratamentos mais conservadores e de maior rapidez no reparo para um resultado funcional e estético satisfatório. O tratamento convencional consiste no uso de medicamentos tópicos e no enxerto de pele natural ou sintética. Alternativamente, a terapia laser utiliza o processo de ablação para remoção do tecido queimado necrosado, devido ao não contato mecânico, à rapidez na aplicação e alcance a áreas de difícil acesso. Deste modo, a proposta deste estudo é avaliar a viabilidade de utilizar lasers de femtossegundos de altíssima intensidade como coadjuvante no tratamento de pacientes queimados. Para o estudo, foram utilizados 25 ratos da raça Wistar, divididos em grupos de 5 animais: grupos pele sadia, pele queimada, dois tipos de tratamento (desbridamento cirúrgico ou ablação a laser de femtossegundos) e em quatro tempos de acompanhamento do processo cicatricial. Três regiões do dorso dos animais foram expostas a fonte de vapor causando queimadura de terceiro grau. No terceiro dia após a queimadura, uma das regiões foi ablacionada com laser de altíssima intensidade de pulsos ultracurtos ( λ = 785nm, 90 fs, 2 kHz e 10 μJ/pulso); outra recebeu o desbridamento cirúrgico; e a última foi considerada o controle de queimadura. As regiões foram analisados por tomografia por coerência óptica (OCT), histologia, reflectância total atenuada por espectroscopia no infravermelho usando transformada de Fourier (μATR-FTIR), microscopia de fluorescência por excitação de dois fótons (TPEFM) e a técnica de geração de segundo harmônico (SHG), nos dias 3, 5, 7 e 14 após os tratamentos. Os resultados mostraram que nas condições de irradiação utilizadas foi possível obter remoção de debris de queimadura de terceiro grau. As técnicas utilizadas para caracterização do tecido permitiram verificar que em todos os tratamentos houve a promoção da reparação tecidual. No décimo quarto dia, a curva de regeneração mostrou que o coeficiente de atenuação do tecido ablacionado a laser converge para os valores da pele sadia, porém as fibras de colágeno ainda não atingiram a mesma organização das fibras presentes na pele sadia. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
47

Espectroscopia de fluorescência na otimização da terapia fotodinâmica em carcinoma espinocelular de pele e sua avaliação utilizando tomografia por coerência óptica / Fluorescence spectroscopy in the optimization of photodynamic therapy of skin squamous cell carcinoma and its evaluation by optical coherence tomography

GOULART, VIVIANE P. 09 October 2014 (has links)
Made available in DSpace on 2014-10-09T12:33:03Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:05Z (GMT). No. of bitstreams: 0 / A terapia fotodinâmica (PDT) é uma alternativa promissora de tratamento para lesões pré-cancerosas e para câncer de pele não-melanoma, como o carcinoma espinocelular, agressivo e potencialmente metastático. Visando melhorar a eficiência da terapia fotodinâmica de carcinoma espinocelular de pele, este estudo otimizou o tempo para início da terapia, avaliou a eficácia dos fotossensibilizadores ácido aminolevulínico (ALA- 20%) e o metil-ester aminolevulínico (MEALA-10%) e verificou o coeficiente de atenuação relativo à pele normal dos grupos experimentais, por meio de Tomografia por Coerência Óptica. Para a indução do tumor foi realizada a carcinogênese química (DMBA/TPA) por um período de 28 semanas. A espectroscopia de fluorescência foi utilizada para monitoração da emissão da molécula de protoporfirina IX, induzida pelo ALA e MEALA. A aquisição de dados a cada 30 minutos totalizando um período de 360 minutos, permitiu verificar a máxima incorporação de ALA e MEALA em 300 e 330 minutos após a aplicação, respectivamente. Após a otimização foi realizada a PDT, avaliação clínica, histopatológica e análise por OCT dos grupos experimentais, por meio das quais verificou-se maior eficiência do grupo tratado com MEALA. No período de 20 dias, o percentual de lesões com redução de área maior que 50%, foi de 33% na PDT com ALA e 83% para o MEALA. Os coeficientes de atenuação ópticos para os grupos com neoplasia foram maiores do que os do grupo controle. Os grupos tratados com PDT apresentaram valores de coeficiente de atenuação que se aproximam dos valores obtidos para a pele sadia, evidenciando a resposta ao tratamento. Entretanto para ambos os fotossensibilizadores utilizados, a PDT mostrou-se eficaz quando iniciada nos tempos determinados neste estudo, e a técnica de OCT mostrou-se uma potencial ferramenta na avaliação deste tratamento. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
48

Studies On Wavefront Estimation And Refraction Corrected Image Reconstruction In Optical Tomography

Datta, G Keshava 04 1900 (has links) (PDF)
No description available.
49

Isogeometric Approach to Optical Tomography

Bateni, Vahid 14 June 2021 (has links)
Optical Tomography is an imaging modality that enhances early diagnosis of disease through use of harmless Near-Infrared rays instead of conventional x-rays. The subsequent images are used to reconstruct the object. However Optical Tomography has not been effectively utilized due to the complicated photon scattering phenomenon and ill-posed nature of the corresponding image reconstruction scheme. The major method for reconstruction of the object is based on an iterative loop that constantly minimizes the difference between the predicted model of photon scattering with acquired images. Currently the most effective method of predicting the photon scattering pattern is the solution of the Radiative Transfer Equation (RTE) using the Finite Elements Method (FEM). However, the conventional FEM uses classical C0 interpolation functions, which have shortcomings in terms of continuity of the solution over the domain as well as proper representation of geometry. Hence higher discretization is necessary to maintain accuracy of gradient-based results which may significantly increase the computational cost in each iteration. This research implements the recently developed Isogeometric Approach (IGA) and particularly IGA-based FEM to address the aforementioned issues. The IGA-based FEM has the potential to enhance adaptivity and reduce the computational cost of discretization schemes. The research in this study applies the IGA method to solve the RTE with the diffusion approximation and studies its behavior in comparison to conventional FEM. The results show comparison of the IGA-based solution with analytical and conventional FEM solutions in terms of accuracy and efficiency. While both methods show high levels of accuracy in reference to the analytical solution, the IGA results clearly excel in accuracy. Furthermore, FE solutions tend to have shorter runtimes in low accuracy results. However, in higher accuracy solutions, where it matters the most, the IGA proves to be considerably faster. / Doctor of Philosophy / CT scans can save lives by allowing medical practitioners observe inside the patient's body without use of invasive surgery. However, they use high energy, potentially harmful x-rays to penetrate the organs. Due to limits of the mathematical algorithm used to reconstruct the 3D figure of the organs from the 2D x-ray images, many such images are required. Thus, a high level of x-ray exposure is necessary, which in periodic use can be harmful. Optical Tomography is a promising alternative which replaces x-rays with harmless Near-infrared (NIR) visible light. However, NIR photons have lower energy and tend to scatter before leaving the organs. Therefore, an additional algorithm is required to predict the distribution of light photons inside the body and their resulting 2D images. This is called the forward problem of Optical Tomography. Only then, like conventional CT scans, can another algorithm, called the inverse solution, reconstruct the 3D image by diminishing the difference between the predicted and registered images. Currently Optical Tomography cannot replace x-ray CT scans for most cases, due to shortcomings in the forward and inverse algorithms to handle real life usages. One obstacle stems from the fact that the forward problem must be solved numerous times for the inverse solution to reach the correct visualization. However, the current numerical method, Finite Element Method (FEM), has limitations in generating accurate solutions fast enough using economically viable computers. This limitation is mostly caused by the FEM's use of a simpler mathematical construct that requires more computations and is limited in accurately modelling the geometry and shape. This research implements the recently developed Isogeometric Analysis (IGA) and particularly IGA-based FEM to address this issue. The IGA-based FEM uses the same mathematical construct that is used to visualize the geometry for complicated applications such as some animations and computer games. They are also less complicated to apply due to much lower need for partitioning the domain. This study applies the IGA method to solve the forward problem of diffuse Optical Tomography and compare the accuracy and speed of IGA solution to the conventional FEM solution. The comparison reveals that while both methods can reach high accuracy, the IGA solutions are relatively more accurate. Also, while low accuracy FEM solutions have shorter runtimes, in solutions with required higher accuracy levels, the IGA proves to be considerably faster.
50

IN-SITU MONITORING OF THE SELECTIVE LASER MELTING PROCESS VIA OPTICAL TOMOGRAPHY

Seavers, Connor 01 December 2021 (has links)
Selective laser melting (SLM) is a method of additive manufacturing that has become increasingly popular in recent years for fabricating complex components, especially in the medical and aerospace industries. By fabricating components in a layerwise fashion, SLM provides users the freedom to design components based on their desired functionality rather than their manufacturability. The current state-of-the-art for SLM is limited though, as defects induced by the SLM process have proven to greatly alter the material properties of fabricated parts. In addition, traditional post-process nondestructive inspection methods have experienced significant difficulty in accurately detecting these process-induced defects. Therefore, the objective of this study is to investigate methods of processing and analysis for optical in-situ monitoring data recorded during SLM fabrication of six test samples. Four of the samples were designed with seeded (i.e., intentional) defects located at their center to serve as a reference defect signatures in the resulting in-situ data. An off-axis optical tomography (OT) sensor was used to capture near-infrared (NIR) melt pool emissions during the fabrication of each layer. Image analysis was subsequently performed using a custom squared difference (SD) operator to enhance defect signatures in the OT data. Results from the SD operator were then used to perform k-means clustering to partition the data into k relevant clusters, where the optimal number of k clusters for each image is employed as metric for detecting the onset of defects in the samples. By employing OT image data from samples containing seeded intentional defects, the k-means clustering approach was investigated as a method of defect detection for the in-situ OT images. Results showed that the SD operator is capable of elucidating anomalous signatures in the in-situ data. However, variations within the SD distributions ultimately limited detection capabilities as the output from k-means clustering was unable to accurately distinguish the seeded defects from the fused regions of material.

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