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You searched for subject:(Axial diffusivity). Showing records 1 – 3 of 3 total matches.

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1. Lyra, Katarina Paz de. Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal.

Degree: PhD, Radiologia, 2015, University of São Paulo

INTRODUÇÃO: Epilepsia do lobo temporal mesial (ELTM) por esclerose hipocampal (EH) é a forma de epilepsia focal mais comum na idade adulta e a causa mais frequente de refratariedade ao tratamento clínico. Apesar de se tratar de uma patologia da substância cinzenta, alguns estudos, por meio da imagem por tensor de difusão (diffusion tensor imaging-DTI), têm demonstrado alteração da substância branca temporal e extratemporal nestes pacientes. O corpo caloso (CC) é a maior comissura cerebral conectando áreas corticais homólogas de ambos os hemisférios cerebrais e tem sido implicado na propagação da atividade epiléptica. O objetivo principal do presente estudo foi avaliar possíveis alterações no CC de pacientes com ELTM-EH pela técnica de DTI e verificar se essas dependem da lateralidade da EH e da concordância entre os exames de ressonância magnética (RM) e os exames de vídeo-eletroencefalograma (EEG). Como objetivo secundário, também avaliou-se se estas alterações se correlacionavam com alguma variável clínica ou com as medidas volumétricas do CC. MÉTODOS: 42 pacientes com ELTM-EH (idades: 20-54 anos) e 30 voluntários saudáveis como grupo controle (idades: 18-53 anos) realizaram exame de RM de crânio, sendo obtidas sequências de DTI com 32 direções de gradiente e imagens volumétricas ponderadas em T1. Os pacientes foram também divididos em subgrupos: EH à direita e EH à esquerda, e em pacientes concordantes e discordantes. Os valores de anisotropia fracionada (AF), difusividade média (DM), difusividade axial (DA), difusividade radial (DR) e os dados volumétricos foram extraídos a partir de cinco segmentos obtidos automaticamente na secção sagital do CC. Foram realizadas comparações dos parâmetros de DTI no CC entre os grupos de pacientes e controles, e entre os subgrupos de pacientes. Foram investigadas correlações entre os parâmetros do tensor de difusão e as variáveis clínicas. As alterações volumétricas no CC dos pacientes com ELTM-EH bem como a correlação dessas alterações com as anormalidades de difusão também foram avaliadas. Considerou-se um valor de p < 0,05 como estatisticamente significativo. RESULTADOS: Nas regiões anterior, médio-posterior e posterior do CC dos pacientes, observaram-se redução da AF e aumento da DM e da DR, em relação aos controles. A DA manteve-se inalterada. Não foram demonstradas diferenças nos padrões de alteração de difusão entre os pacientes com EH à direita e com EH à esquerda, nem entre pacientes concordantes e discordantes. Não foram observadas correlações significativas entre os parâmetros do tensor de difusão com a idade ao evento inicial, idade de início da epilepsia, tempo de doença, tempo de epilepsia, período de latência e frequência de crises. No entanto, pacientes que apresentaram crise febril como evento precipitante inicial exibiram maior intensidade e extensão das alterações de difusão. Observou-se redução volumétrica difusa do CC, sendo demonstrada correlação negativa significativa entre DM e DR, e o volume nos segmentos central, médio-posterior e posterior, e, ainda,… Advisors/Committee Members: Leite, Claudia da Costa, Otaduy, Maria Concepcion Garcia.

Subjects/Keywords: Anisotropia fracionada; Axial diffusivity; Corpo caloso; Corpus callosum; Diffusion tensor imaging; Difusividade axial; Difusividade média; Difusividade radial; Epilepsia do lobo temporal; Esclerose hipocampal; Fractional anisotropy; Hippocampal sclerosis; Imagem por tensor de difusão; Mean diffusivity; Radial diffusivity; Temporal lobe epilepsy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Lyra, K. P. d. (2015). Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal. (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/5/5151/tde-14092015-100239/ ;

Chicago Manual of Style (16th Edition):

Lyra, Katarina Paz de. “Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal.” 2015. Doctoral Dissertation, University of São Paulo. Accessed October 31, 2020. http://www.teses.usp.br/teses/disponiveis/5/5151/tde-14092015-100239/ ;.

MLA Handbook (7th Edition):

Lyra, Katarina Paz de. “Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal.” 2015. Web. 31 Oct 2020.

Vancouver:

Lyra KPd. Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal. [Internet] [Doctoral dissertation]. University of São Paulo; 2015. [cited 2020 Oct 31]. Available from: http://www.teses.usp.br/teses/disponiveis/5/5151/tde-14092015-100239/ ;.

Council of Science Editors:

Lyra KPd. Avaliação por imagem por tensor de difusão do corpo caloso em pacientes com epilepsia mesial temporal e esclerose hipocampal. [Doctoral Dissertation]. University of São Paulo; 2015. Available from: http://www.teses.usp.br/teses/disponiveis/5/5151/tde-14092015-100239/ ;


University of Bath

2. Zhang, Runtong. Measurement of effective diffusivity : chromatographic method (pellets & monoliths).

Degree: PhD, 2013, University of Bath

This thesis aims to find out the effective diffusivity (Deff) of a porous material – γ-alumina, using an unsteady state method with two inert gases at ambient condition with no reactions. For porous materials, Deff is important because it determines the amount of reactants that transfers to the surface of pores. When Deff is known, the apparent tortuosity factor of γ-alumina is calculated using the parallel pore model. The apparent tortuosity factor is important because: (a) it can be used to back-calculate Deff at reacting conditions; (b) once Deff with reactions is known, the Thiele modulus can be calculated and hence the global reaction rate can be found; (c) apparent tortuosity factor is also important for modelling purposes (e.g. modelling a packed-bed column or a catalytic combustion reactor packed with porous γ-alumina in various shapes and monoliths). Experimental measurements were performed to determine the effective diffusivity of a binary pair of non-reacting gases (He in N2, and N2 in He) in spherical γ-alumina pellets (1 mm diameter), and in γ-alumina washcoated monoliths (washcoat thickness 20 to 60 µm, on 400 cpsi (cells per square inch) cordierite support). The method used is based on the chromatographic technique, where a gas flows through a tube, which is packed with the sample to be tested. A pulse of tracer gas is injected (e.g. using sample loops: 0.1, 0.2, 0.5 ml) and by using an on-line mass spectrometer the response in the outlet of the packed bed is monitored over time. For the spherical pellets, the tube i.d. = 13.8 mm and the packed bed depths were 200 and 400 mm. For monoliths the tube i.d. = 7 mm and the packed lengths were 500 and 1000 mm. When the chromatographic technique was applied to the monoliths, it was observed that experimental errors can be significant, and it is very difficult to interpret the data. However, the technique worked well with the spherical pellets, and the effective diffusivity of He in N2 was 0.75 – 1.38 × 10-7 m2 s-1, and for N2 in He was 1.81 – 3.10 × 10-7 m2 s-1. Using the parallel pore model to back-calculate the apparent tortuosity factor, then a value between 5 to 9.5 was found for the pellets.

Subjects/Keywords: 660.2995; effective diffusivity; tortuosity factor; ?-alumina (pellets and monoliths); chromatographic method; convolution theorem; Pe´clet number; axial dispersion coefficient; adsorption equilibrium constant; first moment and second central moment; chromatographic pulse response curve; packed-bed column and fictitous bed; Gaussian-shaped curves/distribution function; Mercury porosimetry; Nitrogen adsorption analysis

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Zhang, R. (2013). Measurement of effective diffusivity : chromatographic method (pellets & monoliths). (Doctoral Dissertation). University of Bath. Retrieved from https://researchportal.bath.ac.uk/en/studentthesis/measurement-of-effective-diffusivity-chromatographic-method-pellets – monoliths(4ee8c05d-0ad5-484c-867a-0c0375339eb0).html ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352

Chicago Manual of Style (16th Edition):

Zhang, Runtong. “Measurement of effective diffusivity : chromatographic method (pellets & monoliths).” 2013. Doctoral Dissertation, University of Bath. Accessed October 31, 2020. https://researchportal.bath.ac.uk/en/studentthesis/measurement-of-effective-diffusivity-chromatographic-method-pellets – monoliths(4ee8c05d-0ad5-484c-867a-0c0375339eb0).html ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352.

MLA Handbook (7th Edition):

Zhang, Runtong. “Measurement of effective diffusivity : chromatographic method (pellets & monoliths).” 2013. Web. 31 Oct 2020.

Vancouver:

Zhang R. Measurement of effective diffusivity : chromatographic method (pellets & monoliths). [Internet] [Doctoral dissertation]. University of Bath; 2013. [cited 2020 Oct 31]. Available from: https://researchportal.bath.ac.uk/en/studentthesis/measurement-of-effective-diffusivity-chromatographic-method-pellets – monoliths(4ee8c05d-0ad5-484c-867a-0c0375339eb0).html ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352.

Council of Science Editors:

Zhang R. Measurement of effective diffusivity : chromatographic method (pellets & monoliths). [Doctoral Dissertation]. University of Bath; 2013. Available from: https://researchportal.bath.ac.uk/en/studentthesis/measurement-of-effective-diffusivity-chromatographic-method-pellets – monoliths(4ee8c05d-0ad5-484c-867a-0c0375339eb0).html ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352

3. Metwalli, Nader. High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications.

Degree: PhD, Biomedical Engineering, 2010, Georgia Tech

Diffusion-weighted magnetic resonance imaging (MRI) has allowed unprecedented non-invasive mapping of brain neural connectivity in vivo by means of fiber tractography applications. Fiber tractography has emerged as a useful tool for mapping brain white matter connectivity prior to surgery or in an intraoperative setting. The advent of high angular resolution diffusion-weighted imaging (HARDI) techniques in MRI for fiber tractography has allowed mapping of fiber tracts in areas of complex white matter fiber crossings. Raw HARDI images, as a result of elevated diffusion-weighting, suffer from depressed signal-to-noise ratio (SNR) levels. The accuracy of fiber tractography is dependent on the performance of the various methods extracting dominant fiber orientations from the HARDI-measured noisy diffusivity profiles. These methods will be sensitive to and directly affected by the noise. In the first part of the thesis this issue is addressed by applying an objective and adaptive smoothing to the noisy HARDI data via generalized cross-validation (GCV) by means of the smoothing splines on the sphere method for estimating the smooth diffusivity profiles in three dimensional diffusion space. Subsequently, fiber orientation distribution functions (ODFs) that reveal dominant fiber orientations in fiber crossings are then reconstructed from the smoothed diffusivity profiles using the Funk-Radon transform. Previous ODF smoothing techniques have been subjective and non-adaptive to data SNR. The GCV-smoothed ODFs from our method are accurate and are smoothed without external intervention facilitating more precise fiber tractography. Diffusion-weighted MRI studies in amyotrophic lateral sclerosis (ALS) have revealed significant changes in diffusion parameters in ALS patient brains. With the need for early detection of possibly discrete upper motor neuron (UMN) degeneration signs in patients with early ALS, a HARDI study is applied in order to investigate diffusion-sensitive changes reflected in the diffusion tensor imaging (DTI) measures axial and radial diffusivity as well as the more commonly used measures fractional anisotropy (FA) and mean diffusivity (MD). The hypothesis is that there would be added utility in considering axial and radial diffusivities which directly reflect changes in the diffusion tensors in addition to FA and MD to aid in revealing neurodegenerative changes in ALS. In addition, applying adaptive smoothing via GCV to the HARDI data further facilitates the application of fiber tractography by automatically eliminating spurious noisy peaks in reconstructed ODFs that would mislead fiber tracking. Advisors/Committee Members: Hu, Xiaoping (Committee Chair), Carew, John (Committee Co-Chair), Benatar, Michael (Committee Member), Martin, Diego (Committee Member), Oshinski, John (Committee Member).

Subjects/Keywords: Orientation distribution function (ODF); Q-ball imaging (QBI); Smoothing splines on the sphere; Generalized cross-validation (GCV); Funk-Radon transform (FRT); Radial diffusivity; Axial diffusivity; Amyotrophic lateral sclerosis (ALS); Diffusion tensor imaging (DTI); High angular resolution diffusion-weighted imaging; Magnetic resonance imaging; MRI; Brain mapping; Diagnostic imaging; Diffusion magnetic resonance imaging

…x28;ALS) 20 1.3.8.2 Axial (λ||) and radial diffusivity (λ⊥) in… …Diffusivity 90 3.3.3 Axial Diffusivity 90 3.3.4 Radial Diffusivity 90 3.3.5 Added Utility of… …Axial and Radial Diffusivity Measures 91 vii 3.3.6 Lack of Correlation between Diffusion… …extracted mean fractional anisotropy (FA), mean diffusivity (MD), axial… …x28;c) axial diffusivity (λ||) and (d) radial diffusivity (λ… 

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Metwalli, N. (2010). High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/34854

Chicago Manual of Style (16th Edition):

Metwalli, Nader. “High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications.” 2010. Doctoral Dissertation, Georgia Tech. Accessed October 31, 2020. http://hdl.handle.net/1853/34854.

MLA Handbook (7th Edition):

Metwalli, Nader. “High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications.” 2010. Web. 31 Oct 2020.

Vancouver:

Metwalli N. High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications. [Internet] [Doctoral dissertation]. Georgia Tech; 2010. [cited 2020 Oct 31]. Available from: http://hdl.handle.net/1853/34854.

Council of Science Editors:

Metwalli N. High angular resolution diffusion-weighted magnetic resonance imaging: adaptive smoothing and applications. [Doctoral Dissertation]. Georgia Tech; 2010. Available from: http://hdl.handle.net/1853/34854

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