Análise morfométrica voxel-a-voxel de estudos de ressonância magnética do crânio em transtornos psiquiátricos e neurológicos: implementação e otimização de métodos

INTRODUCAO: O processamento de imagens de ressonância magnetica (RM) estrutural tem sido amplamente utilizado em pesquisas neuro-psiquiatricas. Os metodos mais usados para este fim sao a volumetria manual por regioes de interesse (regions of interest - ROIs) e a morfometria baseada no voxel (Voxel-based morphometry - VBM). Nesta tese, foi usado um banco de imagens de pacientes diagnosticados com transtorno-obsessivo compulsivo (TOC) (n=19) e controles saudaveis (n=15), as quais foram processadas nas duas tecnicas de analise morfometrica denominadas VBM padrao e VBM otimizado. Foram comparados os resultados obtidos com tais metodos automatizados de VBM versus metodo de ROIs, e comparou-se tambem a incidencia de artefatos de normalizacao espacial e segmentacao entre o VBM padrao e o otimizado. METODOS: As imagens foram processadas usando VBM com o programa Statistical Parametric Mapping (SPM), e ROIs foram desenhadas sobre as regioes cerebrais adjacentes aos ventriculos laterais usando o programa MRIcro. O processamento pelo VBM padrao incluiu normalizacao das imagens para um molde anatomico pre-definido, segmentacao em compartimentos de substância cinzenta, branca e liquor, suavizacao com filtro gaussiano (12mm), e comparacoes estatisticas usando o modelo linear geral. Para o VBM otimizado, foram construidos moldes customizados para o proprio estudo. Utilizando estes moldes, as imagens foram segmentadas e normalizadas para cada compartimento cerebral, gerando parâmetros para que a imagem original pudesse ser normalizada de forma mais precisa. Apos esta segunda normalizacao as imagens foram segmentadas, moduladas pelo determinante jacobiano, suavizadas com filtro gaussiano (12mm), e comparadas estatisticamente. As ROIs foram desenhadas seguindo padroes estabelecidos na literatura internacional. RESULTADOS: Para as regioes cerebrais nas quais se previa a priori a presenca de anormalidades associadas ao TOC, o VBM otimizado mostrou alteracoes volumetricas de... INTRODUCTION: Processing methods for magnetic resonance imaging (MRI) brain data have been largely used in research studies of psychiatric disorders. The techniques most widely used for this purpose are manual volumetry using regions of interest (ROIs) and voxel-based morphometry (VBM). In this thesis, images from a databank of patients diagnosed with obsessive-compulsive disorder (OCD) (n=19) and healthy controls (n=15) were processed using the two VBM methods, namely standard and optimized VBM. The results obtained with those two automated methods were compared to the ROI approach, and the presence of artifacts of spatial normalization and image segmentation were also compared between standard and optimized VBM. METHODS: Image processing using VBM was conducted with the Statistical Parametric Mapping (SPM) program, and the ROIs were drawn over the brain regions adjacent to the lateral ventricles using the MRIcro program. The standard VBM processing included normalization of images to a pre-defined template, segmentation in gray matter, white matter and cerebrospinal fluid compartments, gaussian smoothing (12mm), and statistical comparisons using the general linear model. For optimized VBM, customized templates were built specifically for the study. Using these templates, images were segmented and spatially normalized for each brain compartment, generating parameters that allowed spatial normalization of images with greater precision. After such second normalization, images were segmented, modulated using the jacobian determinants, smoothed with a gaussian filter (12mm), and compared statistically. The ROIs were built using guidelines established in the previous international literature. RESULTS: For the brain regions in which abnormalities in association with OCD were predicted a priori, optimized VBM showed gray matter changes in the OCD group relative to controls, including reduced volume of the anterior cingulate gyrus, and increased volume of the...