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1.
Hum Brain Mapp ; 39(12): 4643-4651, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30253021

RESUMO

Tensor-based morphometry (TBM) performed using T1-weighted images (T1WIs) is a well-established method for analyzing local morphological changes occurring in the brain due to normal aging and disease. However, in white matter regions that appear homogeneous on T1WIs, T1W-TBM may be inadequate for detecting changes that affect specific pathways. In these regions, diffusion tensor MRI (DTI) can identify white matter pathways on the basis of their different anisotropy and orientation. In this study, we propose performing TBM using deformation fields constructed using all scalar and directional information provided by the diffusion tensor (DTBM) with the goal of increasing sensitivity in detecting morphological abnormalities of specific white matter pathways. Previously, mostly fractional anisotropy (FA) has been used to drive registration in diffusion MRI-based TBM (FA-TBM). However, FA does not have the directional information that the tensors contain, therefore, the registration based on tensors provides better alignment of brain structures and better localization of volume change. We compare our DTBM method to both T1W-TBM and FA-TBM in investigating differences in brain morphology between patients with complicated hereditary spastic paraplegia of type 11 (SPG11) and a group of healthy controls. Effect size maps of T1W-TBM of SPG11 patients showed diffuse atrophy of white matter. However, DTBM indicated that atrophy was more localized, predominantly affecting several long-range pathways. The results of our study suggest that DTBM could be a powerful tool for detecting morphological changes of specific white matter pathways in normal brain development and aging, as well as in degenerative disorders.


Assuntos
Imagem de Tensor de Difusão/métodos , Paraplegia Espástica Hereditária/patologia , Substância Branca/patologia , Adulto , Atrofia/patologia , Feminino , Humanos , Masculino , Paraplegia Espástica Hereditária/diagnóstico por imagem , Substância Branca/diagnóstico por imagem
2.
Hum Brain Mapp ; 36(12): 4745-57, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26350492

RESUMO

It has been reported that mechanical vibrations of the magnetic resonance imaging scanner could produce spurious signal dropouts in diffusion-weighted images resulting in artifactual anisotropy in certain regions of the brain with red appearance in the Directionally Encoded Color maps. We performed a review of the frequency of this artifact across pediatric studies, noting differences by scanner manufacturer, acquisition protocol, as well as weight and position of the subject. We also evaluated the ability of automated and quantitative methods to detect this artifact. We found that the artifact may be present in over 50% of data in certain protocols and is not limited to one scanner manufacturer. While a specific scanner had the highest incidence, low body weight and positioning were also associated with appearance of the artifact for both scanner types evaluated, making children potentially more susceptible than adults. Visual inspection remains the best method for artifact identification. Software for automated detection showed very low sensitivity (10%). The artifact may present inconsistently in longitudinal studies. We discuss a published case report that has been widely cited and used as evidence to set policy about diagnostic criteria for determining vegetative state. That report attributed longitudinal changes in anisotropy to white matter plasticity without considering the possibility that the changes were caused by this artifact. Our study underscores the need to check for the presence of this artifact in clinical studies, analyzes circumstances for when it may be more likely to occur, and suggests simple strategies to identify and potentially avoid its effects.


Assuntos
Artefatos , Encéfalo/patologia , Imagem de Difusão por Ressonância Magnética , Pediatria , Vibração/efeitos adversos , Adolescente , Adulto , Análise de Variância , Anisotropia , Mapeamento Encefálico , Distribuição de Qui-Quadrado , Criança , Bases de Dados Factuais/estatística & dados numéricos , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Estudos Retrospectivos
3.
Neuroimage ; 106: 284-99, 2015 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-25433212

RESUMO

We propose an echo planar imaging (EPI) distortion correction method (DR-BUDDI), specialized for diffusion MRI, which uses data acquired twice with reversed phase encoding directions, often referred to as blip-up blip-down acquisitions. DR-BUDDI can incorporate information from an undistorted structural MRI and also use diffusion-weighted images (DWI) to guide the registration, improving the quality of the registration in the presence of large deformations and in white matter regions. DR-BUDDI does not require the transformations for correcting blip-up and blip-down images to be the exact inverse of each other. Imposing the theoretical "blip-up blip-down distortion symmetry" may not be appropriate in the presence of common clinical scanning artifacts such as motion, ghosting, Gibbs ringing, vibrations, and low signal-to-noise. The performance of DR-BUDDI is evaluated with several data sets and compared to other existing blip-up blip-down correction approaches. The proposed method is robust and generally outperforms existing approaches. The inclusion of the DWIs in the correction process proves to be important to obtain a reliable correction of distortions in the brain stem. Methods that do not use DWIs may produce a visually appealing correction of the non-diffusion weighted images, but the directionally encoded color maps computed from the tensor reveal an abnormal anatomy of the white matter pathways.


Assuntos
Artefatos , Encéfalo/anatomia & histologia , Imagem de Difusão por Ressonância Magnética/métodos , Imagem Ecoplanar/métodos , Aumento da Imagem/métodos , Processamento de Imagem Assistida por Computador/métodos , Humanos , Substância Branca/anatomia & histologia
4.
Proc Natl Acad Sci U S A ; 111(46): 16574-9, 2014 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-25368179

RESUMO

Tractography based on diffusion-weighted MRI (DWI) is widely used for mapping the structural connections of the human brain. Its accuracy is known to be limited by technical factors affecting in vivo data acquisition, such as noise, artifacts, and data undersampling resulting from scan time constraints. It generally is assumed that improvements in data quality and implementation of sophisticated tractography methods will lead to increasingly accurate maps of human anatomical connections. However, assessing the anatomical accuracy of DWI tractography is difficult because of the lack of independent knowledge of the true anatomical connections in humans. Here we investigate the future prospects of DWI-based connectional imaging by applying advanced tractography methods to an ex vivo DWI dataset of the macaque brain. The results of different tractography methods were compared with maps of known axonal projections from previous tracer studies in the macaque. Despite the exceptional quality of the DWI data, none of the methods demonstrated high anatomical accuracy. The methods that showed the highest sensitivity showed the lowest specificity, and vice versa. Additionally, anatomical accuracy was highly dependent upon parameters of the tractography algorithm, with different optimal values for mapping different pathways. These results suggest that there is an inherent limitation in determining long-range anatomical projections based on voxel-averaged estimates of local fiber orientation obtained from DWI data that is unlikely to be overcome by improvements in data acquisition and analysis alone.


Assuntos
Conectoma/métodos , Imagem de Difusão por Ressonância Magnética/métodos , Imagem de Tensor de Difusão/métodos , Macaca mulatta/anatomia & histologia , Algoritmos , Animais , Transporte Axonal , Axônios/ultraestrutura , Água Corporal , Meios de Contraste , Difusão , Imagem de Difusão por Ressonância Magnética/estatística & dados numéricos , Imagem de Tensor de Difusão/estatística & dados numéricos , Gadolínio DTPA , Leucina/farmacocinética , Masculino , Modelos Neurológicos , Córtex Motor/anatomia & histologia , Lobo Occipital/anatomia & histologia , Prolina/farmacocinética , Curva ROC , Projetos de Pesquisa , Sensibilidade e Especificidade , Trítio/análise , Substância Branca/anatomia & histologia
5.
Med Image Comput Comput Assist Interv ; 17(Pt 1): 218-26, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25333121

RESUMO

In this work we propose a novel method to correct echo planar imaging (EPI) distortions in diffusion MRI data acquired with reversed phase encoding directions ("blip-up blip-down" acquisitions). The transformation model is symmetric, diffeomorphic and capable of capturing large deformations. It can take advantage of a structural MRI target and include the contribution of diffusion weighted images, in addition to EPI images acquired without diffusion sensitization. The proposed correction significantly outperform existing strategies, assuring anatomically accurate characterization of the orientation, mean diffusivity, and anisotropy of white matter structures in the human brain.


Assuntos
Encéfalo/anatomia & histologia , Imagem de Tensor de Difusão/métodos , Imagem Ecoplanar/métodos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Reconhecimento Automatizado de Padrão/métodos , Técnica de Subtração , Algoritmos , Humanos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
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