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Search Results: 1 - 10 of 604 matches for " Maxime Descoteaux "
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Diffusion Maps Clustering for Magnetic Resonance Q-Ball Imaging Segmentation
Demian Wassermann,Maxime Descoteaux,Rachid Deriche
International Journal of Biomedical Imaging , 2008, DOI: 10.1155/2008/526906
Abstract: White matter fiber clustering aims to get insight about anatomical structures in order to generate atlases, perform clear visualizations, and compute statistics across subjects, all important and current neuroimaging problems. In this work, we present a diffusion maps clustering method applied to diffusion MRI in order to segment complex white matter fiber bundles. It is well known that diffusion tensor imaging (DTI) is restricted in complex fiber regions with crossings and this is why recent high-angular resolution diffusion imaging (HARDI) such as Q-Ball imaging (QBI) has been introduced to overcome these limitations. QBI reconstructs the diffusion orientation distribution function (ODF), a spherical function that has its maxima agreeing with the underlying fiber populations. In this paper, we use a spherical harmonic ODF representation as input to the diffusion maps clustering method. We first show the advantage of using diffusion maps clustering over classical methods such as N-Cuts and Laplacian eigenmaps. In particular, our ODF diffusion maps requires a smaller number of hypothesis from the input data, reduces the number of artifacts in the segmentation, and automatically exhibits the number of clusters segmenting the Q-Ball image by using an adaptive scale-space parameter. We also show that our ODF diffusion maps clustering can reproduce published results using the diffusion tensor (DT) clustering with N-Cuts on simple synthetic images without crossings. On more complex data with crossings, we show that our ODF-based method succeeds to separate fiber bundles and crossing regions whereas the DT-based methods generate artifacts and exhibit wrong number of clusters. Finally, we show results on a real-brain dataset where we segment well-known fiber bundles.
Local Water Diffusion Phenomenon Clustering From High Angular Resolution Diffusion Imaging (HARDI)
Romain Giot,Christophe Charrier,Maxime Descoteaux
Computer Science , 2012,
Abstract: The understanding of neurodegenerative diseases undoubtedly passes through the study of human brain white matter fiber tracts. To date, diffusion magnetic resonance imaging (dMRI) is the unique technique to obtain information about the neural architecture of the human brain, thus permitting the study of white matter connections and their integrity. However, a remaining challenge of the dMRI community is to better characterize complex fiber crossing configurations, where diffusion tensor imaging (DTI) is limited but high angular resolution diffusion imaging (HARDI) now brings solutions. This paper investigates the development of both identification and classification process of the local water diffusion phenomenon based on HARDI data to automatically detect imaging voxels where there are single and crossing fiber bundle populations. The technique is based on knowledge extraction processes and is validated on a dMRI phantom dataset with ground truth.
Real-time multi-peak tractography for instantaneous connectivity display
Maxime Chamberland,Kevin Whittingstall,David Fortin,David Mathieu,Maxime Descoteaux
Frontiers in Neuroinformatics , 2014, DOI: 10.3389/fninf.2014.00059
Abstract: The computerized process of reconstructing white matter tracts from diffusion MRI (dMRI) data is often referred to as tractography. Tractography is nowadays central in structural connectivity since it is the only non-invasive technique to obtain information about brain wiring. Most publicly available tractography techniques and most studies are based on a fixed set of tractography parameters. However, the scale and curvature of fiber bundles can vary from region to region in the brain. Therefore, depending on the area of interest or subject (e.g., healthy control vs. tumor patient), optimal tracking parameters can be dramatically different. As a result, a slight change in tracking parameters may return different connectivity profiles and complicate the interpretation of the results. Having access to tractography parameters can thus be advantageous, as it will help in better isolating those which are sensitive to certain streamline features and potentially converge on optimal settings which are area-specific. In this work, we propose a real-time fiber tracking (RTT) tool which can instantaneously compute and display streamlines. To achieve such real-time performance, we propose a novel evolution equation based on the upsampled principal directions, also called peaks, extracted at each voxel of the dMRI dataset. The technique runs on a single Computer Processing Unit (CPU) without the need for Graphical Unit Processing (GPU) programming. We qualitatively illustrate and quantitatively evaluate our novel multi-peak RTT technique on phantom and human datasets in comparison with the state of the art offline tractography from MRtrix, which is robust to fiber crossings. Finally, we show how our RTT tool facilitates neurosurgical planning and allows one to find fibers that infiltrate tumor areas, otherwise missing when using the standard default tracking parameters.
Dipy, a library for the analysis of diffusion MRI data
Eleftherios Garyfallidis,Matthew Brett,Bagrat Amirbekian,Ariel Rokem,Stefan van der Walt,Maxime Descoteaux,Ian Nimmo-Smith
Frontiers in Neuroinformatics , 2014, DOI: 10.3389/fninf.2014.00008
Abstract: Diffusion Imaging in Python (Dipy) is a free and open source software project for the analysis of data from diffusion magnetic resonance imaging (dMRI) experiments. dMRI is an application of MRI that can be used to measure structural features of brain white matter. Many methods have been developed to use dMRI data to model the local configuration of white matter nerve fiber bundles and infer the trajectory of bundles connecting different parts of the brain. Dipy gathers implementations of many different methods in dMRI, including: diffusion signal pre-processing; reconstruction of diffusion distributions in individual voxels; fiber tractography and fiber track post-processing, analysis and visualization. Dipy aims to provide transparent implementations for all the different steps of dMRI analysis with a uniform programming interface. We have implemented classical signal reconstruction techniques, such as the diffusion tensor model and deterministic fiber tractography. In addition, cutting edge novel reconstruction techniques are implemented, such as constrained spherical deconvolution and diffusion spectrum imaging (DSI) with deconvolution, as well as methods for probabilistic tracking and original methods for tractography clustering. Many additional utility functions are provided to calculate various statistics, informative visualizations, as well as file-handling routines to assist in the development and use of novel techniques. In contrast to many other scientific software projects, Dipy is not being developed by a single research group. Rather, it is an open project that encourages contributions from any scientist/developer through GitHub and open discussions on the project mailing list. Consequently, Dipy today has an international team of contributors, spanning seven different academic institutions in five countries and three continents, which is still growing.
Leishmania promastigotes: building a safe niche within macrophages
Neda Moradin,Albert Descoteaux
Frontiers in Cellular and Infection Microbiology , 2012, DOI: 10.3389/fcimb.2012.00121
Abstract: Upon their internalization by macrophages, Leishmania promastigotes inhibit phagolysosome biogenesis. The main factor responsible for this inhibition is the promastigote surface glycolipid lipophosphoglycan (LPG). This glycolipid has a profound impact on the phagosome, causing periphagosomal accumulation of F-actin and disruption of phagosomal lipid microdomains. Functionally, this LPG-mediated inhibition of phagosome maturation is characterized by an impaired assembly of the NADPH oxidase and the exclusion of the vesicular proton-ATPase from phagosomes. In this chapter, we review the current knowledge concerning the nature of the intra-macrophage compartment in which Leishmania donovani promastigotes establish infection. We also describe how LPG enables this parasite to remodel the parasitophorous vacuole.
Useful or Not? How Schizophrenic Patients Process the Relevance of a Visual Stimulus  [PDF]
Maxime Bubrovszky, Pierre Thomas
Journal of Behavioral and Brain Science (JBBS) , 2011, DOI: 10.4236/jbbs.2011.13015
Abstract: Introduction: The impairment of relevant information selection results in clinical symptoms of schizophrenia. Previous studies assessing visual modality, have reported an impairment of automatic sensory information processing related to abnormal irrelevant stimuli processing. In healthy subjects, neurophysiologic studies have distinguished two early posterior components which the second could be considered as a deviant processing marker. We propose to explore early selective properties of attention in acute patients using event related potential (ERP) methods. We hypothesize an impairment of the detection of deviant stimuli processing, supported by sensory integration neural region. Materiel and method: Ten patients suffering from an acute episode of schizophrenia and ten controls were assessed with a simple three stimuli oddball paradigm analysed by principal components analysis (PCA) method which allows to separate overlapping components and to evaluate their modifications. Result: PCA distinguished two posterior negative components between 100 and 230 msec. The early one was not different between controls and patients. The later one was significantly decreased in the patients group. Discussion: two different physiological components involved in stimuli detection were clearly isolated. The earliest, reflecting elementary perceptive process seems to be preserved in patients with acute schizophrenia whereas the later component, reflecting integrative processing involved in detection of deviance was impaired. These results could be a clue to understand clinical distractibility.
The Leishmania donovani Lipophosphoglycan Excludes the Vesicular Proton-ATPase from Phagosomes by Impairing the Recruitment of Synaptotagmin V
Adrien F. Vinet,Mitsunori Fukuda,Salvatore J. Turco,Albert Descoteaux
PLOS Pathogens , 2009, DOI: 10.1371/journal.ppat.1000628
Abstract: We recently showed that the exocytosis regulator Synaptotagmin (Syt) V is recruited to the nascent phagosome and remains associated throughout the maturation process. In this study, we investigated the possibility that Syt V plays a role in regulating interactions between the phagosome and the endocytic organelles. Silencing of Syt V by RNA interference revealed that Syt V contributes to phagolysosome biogenesis by regulating the acquisition of cathepsin D and the vesicular proton-ATPase. In contrast, recruitment of cathepsin B, the early endosomal marker EEA1 and the lysosomal marker LAMP1 to phagosomes was normal in the absence of Syt V. As Leishmania donovani promastigotes inhibit phagosome maturation, we investigated their potential impact on the phagosomal association of Syt V. This inhibition of phagolysosome biogenesis is mediated by the virulence glycolipid lipophosphoglycan, a polymer of the repeating Galβ1,4Manα1-PO4 units attached to the promastigote surface via an unusual glycosylphosphatidylinositol anchor. Our results showed that insertion of lipophosphoglycan into ganglioside GM1-containing microdomains excluded or caused dissociation of Syt V from phagosome membranes. As a consequence, L. donovani promatigotes established infection in a phagosome from which the vesicular proton-ATPase was excluded and which failed to acidify. Collectively, these results reveal a novel function for Syt V in phagolysosome biogenesis and provide novel insight into the mechanism of vesicular proton-ATPase recruitment to maturing phagosomes. We also provide novel findings into the mechanism of Leishmania pathogenesis, whereby targeting of Syt V is part of the strategy used by L. donovani promastigotes to prevent phagosome acidification.
Lipooxygenase inhibition in osteoarthritis: a potential symptomatic and disease modifying effect?
Maxime Dougados
Arthritis Research & Therapy , 2008, DOI: 10.1186/ar2490
Abstract: In the previous issue of Arthritis Research & Therapy, Sengupta and colleagues [1] report the results of a short-term placebo randomized controlled trial evaluating both the symptomatic and biological effects of the compound 5-Loxin?, which is a gum resin extracted from an ancient herb. Despite the small sample size (25 patients per arm) and the short duration of this trial (3 months), the reported results are interesting and intriguing for several reasons.In the field of rheumatology, most new therapeutic compounds are based on our knowledge of the pathophysiological pathways of the disease (for example, targeted therapies against cytokines such as tumor necrosis factor (TNF), interleukin-6, and so on) or against some specific enzyme (for example, cyclooxygenases). The compound evaluated in the trial reported by Sengupta and colleagues [1] is in fact derived from an ancient herb, Boswella. Because of the empirically observed anti-arthritic and analgesic effects of this compound, researchers have tried to understand its mechanism of action. In vitro data suggest that 5-Loxin? might be considered as a potent lipooxygenase inhibitor but also, at a lower magnitude, an inhibitor of the TNFα-induced gene expression of matrix metalloproteinases. Such in vitro findings have to be kept in mind when interpreting the results of the trial. In particular, should we consider that the observed symptomatic treatment effect is related to the lipooxygenase inhibition, to the anti-TNFα inhibition, to both, or to an as yet unknown mechanism?This trial has been conducted in India. The researchers have to be congratulated because of the high quality of both the design, the conduct, the analysis and the reporting of the trial.The observed symptomatic placebo effect is of a similar magnitude as those observed in previous placebo randomized controlled trials in this condition [2,3]. The observed symptomatic effect (for example, the differences in the changes in the active minus the placebo
TOPOGRAFíA Y ASTRONOMíA: DOS HERRAMIENTAS DE APOYO EN ARQUEOLOGíA
Boccas,Maxime;
Chungará (Arica) , 2004, DOI: 10.4067/S0717-73562004000400039
Abstract: in the last decade, multidisciplinary archaeoastronomical investigations have demonstrated some increasing maturity and have brought significant knowledge to prehistory. alignment investigations in a prehistoric site are based on topographic analysis, which allows sometimes to show the relationship that people established with their terrestrial environment (sacred landscape). in some cases, a relationship with celestial objects, especially the sun at the solstice time, was also present in order to measure time and thus organize labor and ritual activities. we will recall some basic concepts for an archaeoastronomy investigation, then we focus on some interesting examples worldwide, and finally we present a few chilean sites that could exhibit archaeoastronomical features
Las movilizaciones sociales: aportes recientes de la sociología francesa
Haubert, Maxime;
Revista mexicana de sociología , 2011,
Abstract: although french social sciences have lost much of their leadership regarding the study of social mobilizations, they have maintained significant specificities, particularly the key explanatory role attributed to relations with global society and the state and the demand for civil rights (as in the suburban riots of 1995). recent studies tend to ignore labor conflicts, focusing instead on the movements of those who have been excluded or marginalized and their militant leaders.
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