Thesis (M.Sc.) - Carleton University, 2008. / Includes bibliographical references (p. 77-81). Also available in electronic format on the Internet.

Thesis (M. Sc.)--Carleton University, 2001. / Includes bibliographical references (p. 79-84). Also available in electronic format on the Internet.

Thesis (M. Sc.)--Carleton University, 2001. / Includes bibliographical references (p. 64-71). Also available in electronic format on the Internet.

Thesis (M. S.)--Nuclear and Radiological Engineering and Medical Physics, Georgia Institute of Technology, 2010. / Committee Chair: Rahnema, Farzad; Committee Member: Wang, Chris; Committee Member: Zhang, Dingkang. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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A Neuroimagem Funcional evoluiu muito nos últimos anos com o aparecimento de técnicas como Positron Emission Tomography ou PET (Tomógrafo por Emissão de Pósitrons) e Functional Magnetic Ressonance Image ou fMRI (Imagem de RessonÂncia Magnética Funcional) [Belliveau et al., 1991]. Elas permitem a observação de atividade no cérebro com uma resolução de alguns milímetros, e devido a natureza do sinal medido, com uma resolução temporal da ordem de 5 segundos [Kim et al., 1997]. Magnetoencefalografia e Eletroencefalografia (M/EEG), por outro lado, possuem uma resoluçao temporal da ordem de milissegundos, já que o sinal é produzido pela movimentação do íons através das membranas celulares [Nunez and Srinivasan, 2006]. Porém a sua resoluçeo espacial é muito baixa jé que tipicamente são problemas mal postos, com muito mais variáveis do que dados. Um equipamento de M/EEG de alta resolução possui da ordem de O(200) canais, que permitem medidas do campo magnético (para o MEG) ou do potencial elétrico (para o EEG) em O(200) posições em torno da cabeça. Para uma escala com resolução de ordem l existem (L /l )3 variáveis, onde L = aprox. 15cm. Neste trabalho procuramos estudar métodos para aumentar a resolução espacial das técnicas de EEG, pois o mapeamento funcional do cérebro humano esta intimamente relacionado à localização da atividade no espaço bem como no tempo [Friston, 2009] (muitas relativo ao momento de um estímulo externo). Todo o trabalho de localização de fontes para EEG pode ser facilmente estendido para MEG. Métodos Bayesianos são o cenário natural para lidar com problemas mal postos [Wipf and Nagarajan, 2009]. Existem, essencialmente, duas direções nas quais os algoritmos Bayesianos podem ser melhoradas, através da construção de uma melhor verossimilhança ou uma distribuição a Priori. Embora reconheçamos que avanços importantes podem ser feitos no direção anterior, aqui nos concentramos na segunda. Neste trabalho nós introduzimos um método multiescala para construir uma melhor distribuição a Priori. Uma idéia similar foi estudada dentro do contexto mais simples de fMRI [Amaral et al., 2004]. Muitos novos problemas aparecem ao lidar com o caráter vetorial do EEG. O mais importante, é a construção de um conjunto de superfícies renormalizadas que aproximam a região cortical onde a fonte de atividade esta localizada e o problema relacionado de de nir as variáveis relevantes para representar o cérebro em uma escala com menor resolução. A validação do novo algoritmo é sempre um problema essencial. Nós apresentamos resultados que sugerem, em dados simulados, que nosso método pode ser uma alternativa válida para os atuais algoritmos, julgando ambos pela taxa de erros na localização de fontes bem como pelo tempo que eles levam para convergir. / Functional Neuroimaging has evolved in the last few decades with the introduction of techniques such as Positron Emission Tomography or PET and Functional Magnetic Ressonance Image or fMRI [Belliveau et al., 1991]. These allow observing brain activity with a resolution of a few millimeters and, due to the nature of the signal, a time resolution of the order of 5 seconds [Kim et al., 1997]. M/EEG, on the other hand, have a millisecond time resolution, since the signal is produced by the transport of ions through cell membranes [Nunez and Srinivasan, 2006]. However their space resolution is much lower since these are typically ill posed problems with many more unknowns than data points. A high resolution M/EEG has of the order of O(200) data channels, which allow measuring the magnetic or electric field at O(200) positions around the head. For a resolution scale of order l there are O(L l )3 variables, where L = 15cm. In this work we aim at studying methods to increase the spatial resolution of EEG techniques, since functional mapping of the human brain is intimately related to the localization of the activity in space as well as in time [Friston, 2009] (often relative to the time of external stimuli). Any advance in the inverse problem of source localization for EEG can rather easily be extended to deal with MEG. Bayesian methods are the natural setting to deal with ill posed problems [Wipf and Nagarajan, 2009]. There are essentially two directions in which Bayesian algorithms can be improved, by building a better likelihood or a prior distribution. While we recognize that important advances can be done in the former direction we here concentrate in the latter. In this work we introduce a multiscale method to build an improved prior distribution. A similar idea has been studied within an easier context of fMRI [Amaral et al., 2004]. Several new problems appear in dealing with the vectorial character of EEG. The most important, is the construction of a set of renormalized lattices that approximate the cortex region where the source activity is located and the related problem of de ning the relevant variables in coarser scale representation of the cortex. Validation of a new algorithm is always an essential problem. We present results which suggest on simulated data, that our method might be a valid alternative to current algorithms, judged both by the rate of errors in source localization as well as by the time it takes to converge.

Permanent breast seed implant brachytherapy (PBSI) is a recently developed form of treatment for early-stage breast cancer which can be completed in a single day procedure. Due to the reduced treatment burden, PBSI has the potential to benefit many women. However the technique has not been widely implemented, potentially related to the lack of a standardized, reproducible procedure and a high level of operator dependence. Challenges relating to target visualization uncertainties and the reliance on free-hand 2D ultrasound (US) guidance potentially inhibit adoption of the technique. This work aims to evaluate the current PBSI procedure to identify uncertainties and potential sources of errors in the current technique and develop methods to ameliorate these issues to potentially increase treatment accuracy, standardize the procedure, and reduce user-dependence. A comprehensive assessment of the current PBSI procedure was performed to identify any trends or systematic errors in the placement of seeds and establish the effects of seed placement accuracy on the treatment. Baseline seed placement accuracy, assessed in a 20 patient cohort was observed to be 9(5) mm. Random displacements of seeds from their planned position contributed significantly to the overall accuracy. No trends or systematic errors were observed across the aggregate population, however intra-patient systematic offsets were observed. The potential effects of visualization of the post-lumpectomy cavity (seroma) on treatment delivery was investigated using spatially registered CT and 3DUS images. Planning the treatment on CT, as is standard practice, resulted in less than optimal coverage to target volumes defined on US in the majority of cases. The effects of intra-operative adjustments relating to the visualization differences on the two modalities was assessed by shifting the CT-based treatment plan to centre on the US-defined seroma. Such shifts were shown to potentially contribute to the systematic displacements observed in PBSI delivery, and also had significant dosimetric effects on the planned target volumes. The impact of seroma visualization on PBSI implant accuracy was further assessed through the evaluation of CT and 3DUS images acquired for PBSI patients. Correlations were observed between the seed placement accuracy and the inter-user variability of seroma definition on CT (r = 0.74, p = 0.01) and the volume difference of the seroma on the two modalities (r = 0.65, p = 0.04), indicating that discrepancies in target delineation can impact treatment accuracy. The systematic displacements of the implants were observed to be correlated with the visualization metrics, however random displacements were independent of seroma delineation. Deviations in needle positioning during insertion may not be realized until the implant is complete, thus contributing to the random inaccuracies in seed placement. A purpose built 3DUS scanning system was investigated for its use in guiding needle insertion. Registration of the treatment template with the imaging system was validated to provide accurate target localization for needle insertion. Adjustments and re-insertion of needles under 3DUS guidance provided significant improvements to the needle positioning accuracy. A simulated implant with the guidance system indicated that overall treatment accuracy may be improved through the clinical implementation of such a system. Efforts to improve seroma definition during treatment planning and image guidance during the delivery can significantly increase seed placement accuracy and reduce the need for subjective intra-operative adjustments to the setup and needle positioning. Standardization of such advanced imaging techniques can greatly benefit the PBSI procedure by reducing user dependence and help to promote implementation. / Graduate / 2018-09-22

Orientadores: Eduardo Tavares Costa, Paulo José Cecílio / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-24T11:03:55Z (GMT). No. of bitstreams: 1 Biazotto_Bruna_M.pdf: 4075478 bytes, checksum: 077630eb4f66ca28ec46de7251c31e3f (MD5) Previous issue date: 2013 / Resumo: A experiência clínica em tratamentos radioterápicos de neoplasia de próstata baseia-se no cálculo de doses em meios homogêneos. Entretanto, o feixe de radiação atravessa tecidos de densidades eletrônicas diferentes como os ossos, que alteram a distribuição de dose. Com o advento da tomografia computadorizada e de algoritmos mais avançados que modelam o feixe de radiação, as heterogeneidades entre os tecidos podem ser incorporadas nos planejamentos de tratamentos radioterápicos. Todavia, não há consenso se as alterações na dose por correções de heterogeneidade são significativas. Por tais razões, pretendeu-se no presente trabalho avaliar a necessidade das correções de heterogeneidade em planejamentos de tratamentos radioterápicos de câncer de próstata. Para isso, analisaram-se as médias das diferenças percentuais nas doses em volume alvo e órgãos de risco obtidas em cálculos com e sem correções de heterogeneidade utilizando imagens tomográficas reais de pacientes que trataram dessa neoplasia. Essa avaliação foi realizada para dois métodos de tratamentos diferentes. O primeiro é o conformacional tridimensional (25 casos), algoritmos de cálculo Convolution, Superposition e Fast Superposition do sistema de planejamento XiO/Elekta, feixes de 6 e 10 MV e 4 campos em box. O segundo por intensidade modulada (14 casos), algoritmo de cálculo Pencil Beam Convolution do sistema de planejamento Eclipse/Varian com dois métodos de correção Batho Modificado e Razão Tecido-Ar Equivalente, feixe de 6 MV e geometria de 5 campos oblíquos. As diferenças percentuais médias resultantes nos volumes estudados foram menores que a incerteza aceita atualmente no cálculo de dose de 3% para as duas modalidades de tratamento. Apesar disso, a variabilidade na anatomia dos pacientes, geometria de campos e energia dos feixes apontam para a necessidade de tais correções e a utilização de métodos ainda mais exatos para a diminuição dessa incerteza no futuro / Abstract: Clinical experience in radiotherapy treatments for prostate cancer is based on the calculation of doses in homogeneous media. However, the radiation beam traverses different electron densities in tissues such as bone, altering the dose distribution. With the advent of computed tomography and more advanced algorithms that model the radiation beam, the heterogeneity between tissues can be incorporated in the planning of radiotherapy treatments. However, there is no consensus whether changes in dose for inhomogeneity corrections are significant. For these reasons, this study intended to evaluate the need for inhomogeneity corrections in treatment planning for radiotherapy of prostate cancer. We have analyzed the average percentage differences in doses in the target volume and organs at risk obtained by calculations with and without heterogeneity corrections using actual CT images of patients treated for this cancer. This evaluation was performed for two different methods of treatments. The first is the three-dimensional conformational (25 cases), calculation algorithms Convolution, Superposition and Fast Superposition from the computerized planning system XiO/Elekta, beams of 6 and 10 MV and 4 fields in box. The second by intensity modulated (14 cases), calculation algorithm Pencil Beam Convolution from the computerized planning system Eclipse/Varian with two correction methods Modified Batho and Equivalent Tissue-Air Ratio, 6 MV beam and geometry of 5 oblique fields. The resulting average percentage differences in volumes studied were smaller than the currently accepted uncertainty in the dose calculation of 3% for both treatment modalities. Nevertheless, variability in anatomy of patients, geometry and field energy beams brings the need for these corrections and the use of more accurate methods to reduce this uncertainty in the future / Mestrado / Engenharia Biomedica / Mestra em Engenharia Elétrica

<p>Aluminum is present throughout the environment and in many industrial processes and consumer goods. While very useful in everyday lives, it has no inherent biological functions in humans. High quantities in the human body can be toxic, resulting a range of skeletal, neurological, and hematopoietic effects. A system has been developed to analyze aluminum using the neutron activation analysis (NAA) technique in vivo. NAA was performed with a transportable neutron generator as a neutron source and a high purity germanium (HPGe) detector for spectroscopy. The neutron generator and HPGe detector were completely modelled in MCNP6. Measurements were carried out to evaluate the accuracy of the MCNP6 simulations and to determine the detection capabilities of the system for aluminum. Simulations were also conducted to determine the acceptability of radiation dose to subjects undergoing analysis. The detection limit for the system was evaluated using skeletal bone as a long-term aluminum biomarker. The detection limit was determined to be 3.41 x 10¹ μg of Al per g of dry bone for an irradiation time of six minutes. This detection level is below a point at which physiological effects have been observed in humans. A lower detection level was demonstrated to be possible with a longer irradiation time. The radiation absorbed dose was determined to be 7.30 mGy for an irradiation of six minutes. The system can therefore be utilized as a potential screening and monitoring tool for high skeletal burdens of aluminum that may lead to physiological effects.</p> <p>The simulation and calculation techniques developed herein were applied to a set of human subject data that were acquired for a purpose other than evaluating aluminum. The human subject data included both bone Al from NAA and fingernail Al from mass spectrometry measurements. No significant aluminum signals were observed when assessing the in vivo NAA spectra data. Through simulation and calculation, it was demonstrated that the NAA experimental parameters resulted in an elevated detection limit for aluminum that is above Al skeletal loads observed in healthy individuals. The elevated detection limit prevented the in vivo detection of aluminum in a healthy population, thus confirming the NAA results. </p>