Georges Le Goualher

Mauna Kea Technologies, Lutetia Parisorum, Île-de-France, France

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Publications (33)47.35 Total impact

  • 10/2007;
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    ABSTRACT: Correspondence of cortical structures is difficult to establish in automatic voxel-based non-linear registration of human brains based solely on gradient magnitude images. Experiments with a set of 9 real MRI data volumes demonstrates that the inclusion of 1) L vv-based features or 2) automatically extracted sulci significantly reduce overlap errors for gyri and sulci on the cortex. Mismatch between gyri can be addressed using manually labelled sulci.
    04/2006: pages 307-316;
  • 10/2005;
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    ABSTRACT: This paper presents an integrated endoscope-compatible Fibered Confocal Fluorescence Microscope (FCFM) for medical imaging, the F400.
    07/2004;
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    ABSTRACT: distances can detect a possible genetic encoding. When applied to real data, this study highlighted genetic constraints on the shape of the central sulcus. We found from 10 pairs of monozygotic twins that the intrapair modal distance of the central sulcus was significantly smaller than the interpair modal distance, for both the left central sulcus (Z ##2.66; P < 0.005) and the right central sulcus (Z ##2.26; P < 0.05). Genetic constraints on the definition of the central sulcus shape were confirmed by applying the same experiment to 10 pairs of normal young individuals (Z ##1.39; Z ##0.63, i.e., values not significant at the P < 0.05 level) and 10 pairs of dizygotic twins (Z # 0.47; Z # 0.03, i.e., values not significant at the P < 0.05 level). 2000 Academic Press Key Words: cerebral cortex; central sulcus; Principal Component Analysis; genetic encoding. INTRODUCTION Cortical sulci of the human brain (and their counterpart gyri) form macroscopic anatomical landmarks on the surfac
    07/2004;
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    ABSTRACT: This article describes an original method to measure the velocity of blood cells in microvessels from a single image. The method exploits a motion artifact produced by laser scanning microscope (LSM). Although velocity can be estimated from a single image, we show how a temporal sequence can then be exploited to increase the robustness and accuracy of the estimation. Preliminary experiments show good quantitative results in synthetic images of microvessels, and good qualitative results with real images of microvessels acquired in vivo and in situ at a temporal frequency of ## ##. A quantitative validation of real measurements is under progress with a specific experimental set-up described in the article.
    05/2004;
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    ABSTRACT: This paper presents a novel fibered confocal fluorescence microscopy system (FCFM) specifically designed for the observation of biological tissues in vivo and in situ, in real time, at the cellular level: the Cell-viZio. The Cell-viZio is made of three main components that are described in this paper: i) FibroScan: an opto-electronic unit controlling a laser scanning and data acquisition system; ii) ProFlex: a set of flexible miniaturized optical probes allowing in situ imaging. iii) ImageCell: a dedicated software performing real-time control and image processing. The Cell-viZio provides images with typical characteristics (varying with the optical probe) as follows: image lateral resolution: 2.5 microns; axial resolution: 20 microns; field of view: 160 × 120 microns; optical imaging depth: 80 microns (deeper in transparent tissue); data acquisition frame rate: 12 Hz. Thanks to the miniaturization of flexible optical probes (Φ: down to 350 μm), unprecedented accessibility is made possible. In vivo in situ images of rat bladder and mouse colon obtained endoscopically are presented here for the first time.
    Biomedical Imaging: Nano to Macro, 2004. IEEE International Symposium on; 05/2004
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    ABSTRACT: This article describes an original method to measure the velocity of blood cells in microvessels from a single image. The method exploits a motion artifact produced by laser scanning microscope (LSM). Although velocity can be estimated from a single image, we show how a temporal sequence can then be exploited to increase the robustness and accuracy of the estimation. Preliminary experiments show good quantitative results in synthetic images of microvessels, and good qualitative results with real images of microvessels acquired in vivo and in situ at a temporal frequency of 2 Hz . A quantitative validation of real measurements is under progress with a specific experimental set-up described in the article.
    Proceedings of the 2004 IEEE International Symposium on Biomedical Imaging: From Nano to Macro, Arlington, VA, USA, 15-18 April 2004; 01/2004
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    ABSTRACT: This study investigated the capability of fibered confocal fluorescence microscopy (FCFM) to provide in vivo microvascular observations. FCFM is specifically designed for in vivo in situ observation thanks to a probe composed of a fiber bundle and micro-optics having a diameter as small as 650 microm. In the first part of the study, we compared the main characteristics of FCFM with those of intravital fluorescence microscopy (IFM). A mouse cremaster preparation was used as a common basis to allow for imaging with both modalities. We discussed the feasibility of obtaining quantitative measurements usually provided by IFM in the context of FCFM: morphometry, capillary permeability, functional capillary density, vasoconstriction and dilation effects. In addition, the possibility to visualize fluorescent red blood cells or leukocytes was also evaluated. Phototoxicity issues and limitations of FCFM were also discussed. We showed that FCFM allows observations and measurements usually provided by IFM and that the real-time capability of the system, as well as the flexibility and small diameter of the optical probe enable micro-invasiveness and can extend imaging capabilities for in vivo in situ observations when compared to IFM.
    Journal of Vascular Research 01/2004; 41(5):400-11. · 2.43 Impact Factor
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    ABSTRACT: This paper presents an integrated endoscope-compatible Fibered Confocal Fluorescence Microscope (FCFM) for medical imaging, the F- 400. In situ high resolution images can be obtained thanks to a set of flexible miniaturized optical probes of 0.5 to 1.5 mm diameter that can be inserted through the working channel of an endoscope. We briefly present in this paper the FCFM system, with a particular focus on the image formation and the design of a dedicated image processing software allow- ing for drastically reduce the inherent artifacts occurring when imaging through an image bundle. The goal of the FCFM is to perform optical biopsy (i.e. in vivo and in situ observations of thin sections of biological tissues at the cellular level). As a first step towards this goal, we present here results of a clinical trial assessing the ability of the F-400 to per- form rapid morphologic examination in the endoscopy room of medical specimens (polypectomy).
    Medical Image Computing and Computer-Assisted Intervention -- MICCAI 2004, 7th International Conference Saint-Malo, France, September 26-29, 2004, Proceedings, Part II; 01/2004
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    ABSTRACT: Although numerous methods to register brains of different individuals have been proposed, no work has been done, as far as we know, to evaluate and objectively compare the performances of different nonrigid (or elastic) registration methods on the same database of subjects. In this paper, we propose an evaluation framework, based on global and local measures of the relevance of the registration. We have chosen to focus more particularly on the matching of cortical areas, since intersubject registration methods are dedicated to anatomical and functional normalization, and also because other groups have shown the relevance of such registration methods for deep brain structures. Experiments were conducted using 6 methods on a database of 18 subjects. The global measures used show that the quality of the registration is directly related to the transformation's degrees of freedom. More surprisingly, local measures based on the matching of cortical sulci did not show significant differences between rigid and non rigid methods.
    IEEE Transactions on Medical Imaging 10/2003; · 4.03 Impact Factor
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    ABSTRACT: Although numerous methods to register brains of different individuals have been proposed, few work has been done to evaluate the performances of different registration methods on the same database of subjects. In this paper, we propose an evaluation framework, based on global and local measures of the quality of the registration. Experiments have been conducted for 5 methods, through a database of 18 subjects. We focused more extensively on the registration of cortical landmarks that have a particular relevance in the context of anatomical-functional normalization. For global measures, results show that the quality of the registration is directly related to the transformation's degrees of freedom. However, local measures based on the matching of cortical sulci, did not make it possible to show significant differences between affine and non linear methods.
    IEEE Trans. Med. Imaging. 01/2003; 22:1120-1130.
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    ABSTRACT: Although numerous methods to register brains of different individuals have been proposed, no work has been done, as far as we know, to evaluate and compare objectively the performances of different registration methods on the same database of subjects. In this paper, we propose an evaluation framework, based on global and local measures of the quality of the registration. Experiments have been conducted for 5 methods, through a database of 18 subjects.
    03/2002;
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    ABSTRACT: Motivated by the vast amount of information that is rapidly accumulating about the human brain in digital form, we embarked upon a program in 1992 to develop a four-dimensional probabilistic atlas and reference system for the human brain. Through an International Consortium for Brain Mapping (ICBM) a dataset is being collected that includes 7000 subjects between the ages of eighteen and ninety years and including 342 mono- and dizygotic twins. Data on each subject includes detailed demographic, clinical, behavioural and imaging information. DNA has been collected for genotyping from 5800 subjects. A component of the programme uses post-mortem tissue to determine the probabilistic distribution of microscopic cyto- and chemoarchitectural regions in the human brain. This, combined with macroscopic information about structure and function derived from subjects in vivo, provides the first large scale opportunity to gain meaningful insights into the concordance or discordance in micro- and macroscopic structure and function. The philosophy, strategy, algorithm development, data acquisition techniques and validation methods are described in this report along with database structures. Examples of results are described for the normal adult human brain as well as examples in patients with Alzheimer's disease and multiple sclerosis. The ability to quantify the variance of the human brain as a function of age in a large population of subjects for whom data is also available about their genetic composition and behaviour will allow for the first assessment of cerebral genotype-phenotype-behavioural correlations in humans to take place in a population this large. This approach and its application should provide new insights and opportunities for investigators interested in basic neuroscience, clinical diagnostics and the evaluation of neuropsychiatric disorders in patients.
    Philosophical Transactions of The Royal Society B Biological Sciences 09/2001; 356(1412):1293-322. · 6.23 Impact Factor
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    ABSTRACT: The authors describe the development of a four-dimensional atlas and reference system that includes both macroscopic and microscopic information on structure and function of the human brain in persons between the ages of 18 and 90 years. Given the presumed large but previously unquantified degree of structural and functional variance among normal persons in the human population, the basis for this atlas and reference system is probabilistic. Through the efforts of the International Consortium for Brain Mapping (ICBM), 7,000 subjects will be included in the initial phase of database and atlas development. For each subject, detailed demographic, clinical, behavioral, and imaging information is being collected. In addition, 5,800 subjects will contribute DNA for the purpose of determining genotype– phenotype–behavioral correlations. The process of developing the strategies, algorithms, data collection methods, validation approaches, database structures, and distribution of results is described in this report. Examples of applications of the approach are described for the normal brain in both adults and children as well as in patients with schizophrenia. This project should provide new insights into the relationship between microscopic and macroscopic structure and function in the human brain and should have important implications in basic neuroscience, clinical diagnostics, and cerebral disorders.
    Journal of the American Medical Informatics Association 09/2001; · 3.57 Impact Factor
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    N Kabani, G Le Goualher, D MacDonald, A C Evans
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    ABSTRACT: A validation study was conducted to assess the accuracy of the algorithm developed by MacDonald et al. (1999) for measuring cortical thickness. This algorithm automatically determines the cortical thickness by 3-D extraction of the inner and outer surfaces of the cerebral cortex from an MRI scan. A manual method of tagging the grey-csf and grey-white interface was used on 20 regions (10 cortical areas found in each hemisphere) in 40 MRIs of the brain to validate the algorithm. The regions were chosen throughout the cortex to get broad assessment of the algorithm's performance. Accuracy was determined by an anatomist tagging the csf-grey and grey-white borders of selected gyri and by allowing the algorithm to determine the csf-grey and grey-white borders and the corresponding cortical thickness of the same region. Results from the manual and automatic methods were statistically compared using overall ANOVA and paired t tests for each region. The manual and automatic methods were in agreement for all but 4 of the 20 regions tested. The four regions where there were significant differences between the two methods were the insula left and right, the right cuneus, and the right parahippocampus. We conclude that the automatic algorithm is valid for most of the cortex and provides a viable alternative to manual methods of determining cortical thickness in vivo. However, caution should be taken when measuring the regions mentioned previously where the results of the algorithm can be biased by surrounding grey structures.
    NeuroImage 03/2001; 13(2):375-80. · 6.25 Impact Factor
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    ABSTRACT: Although numerous methods to register brains of dif- ferent individuals have been proposed, no work has been done, as far as we know, to evaluate and objectively compare the perfor- mances of different nonrigid (or elastic) registration methods on the same database of subjects. In this paper, we propose an eval- uation framework, based on global and local measures of the rel- evance of the registration. We have chosen to focus more partic- ularly on the matching of cortical areas, since intersubject regis- tration methods are dedicated to anatomical and functional nor- malization, and also because other groups (7) have shown the rel- evance of such registration methods for deep brain structures. Ex- periments were conducted using 6 methods on a database of 18 subjects. The global measures used show that the quality of the registration is directly related to the transformation's degrees of freedom. More surprisingly, local measures based on the matching of cortical sulci did not show significant differences between rigid and non rigid methods.
    Medical Image Computing and Computer-Assisted Intervention - MICCAI 2001, 4th International Conference, Utrecht, The Netherlands, October 14-17, 2001, Proceedings; 01/2001
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    ABSTRACT: Although numerous methods to register brains of different individuals have been proposed, few work has been done to evaluate the performances of different registration methods on the same database of subjects. In this paper, we propose an evaluation framework, based on global and local measures of the quality of the registration. Experiments have been conducted for 5 methods, through a database of 18 subjects. We focused more extensively on the registration of cortical landmarks that have a particular relevance in the context of anatomical-functional normalization. For global measures, results show that the quality of the registration is directly related to the transformation’s degrees of freedom. However, local measures based on the matching of cortical sulci, did not make it possible to show significant differences between affine and non linear methods.
    12/2000: pages 258-265;
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    ABSTRACT: The location of human area V5 (or MT) has been correlated with the intersection of the ascending limb of the inferior temporal sulcus (ALITS) and the lateral occipital sulcus (LO). This study was undertaken to attempt a replication and quantification of these observations using functional magnetic resonance imaging. V5 was significantly activated in 19 hemispheres with alternating, low contrast, random checkerboard patterns. We confirmed the stereotaxic location of V5 and were able to describe a fairly consistent sulcal pattern in the parieto-temporo-occipital cortex. V5 was usually (95%) buried within a sulcus, most commonly within the inferior temporal sulcus (ITS) (11%), the ascending limb of the ITS (ALITS) (53%) and the posterior continuation of the ITS (26%). The average distance from V5 of two identified anatomical landmarks of V5, the junctions of the LO and the ALITS, and the ITS and ALITS, were both 1 cm. However, the LO-ALITS junction often had to be determined by interpolation (47%), and was not always present even with interpolation (21%). In contrast, the ITS-ALITS junction was always present and V5 was usually (90%) located in a sulcus intersecting with this junction, making it a more reliable landmark for localizing V5 with respect to gross morphological features on individual cortical surfaces.
    Cerebral Cortex 06/2000; 10(5):454-63. · 8.31 Impact Factor
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    ABSTRACT: Principal Component Analysis allows a quantitative description of shape variability with a restricted number of parameters (or modes) which can be used to quantify the difference between two shapes through the computation of a modal distance. A statistical test can then be applied to this set of measurements in order to detect a statistically significant difference between two groups. We have applied this methodology to highlight evidence of genetic encoding of the shape of neuroanatomical structures. To investigate genetic constraint, we studied if shapes were more similar within 10 pairs of monozygotic twins than within interpairs and compared the results with those obtained from 10 pairs of dizygotic twins. The statistical analysis was performed using a Mantel permutation test. We show, using simulations, that this statistical test applied on modal distances can detect a possible genetic encoding. When applied to real data, this study highlighted genetic constraints on the shape of the central sulcus. We found from 10 pairs of monozygotic twins that the intrapair modal distance of the central sulcus was significantly smaller than the interpair modal distance, for both the left central sulcus (Z = -2.66; P < 0.005) and the right central sulcus (Z = -2.26; P < 0.05). Genetic constraints on the definition of the central sulcus shape were confirmed by applying the same experiment to 10 pairs of normal young individuals (Z = -1.39; Z = -0.63, i.e., values not significant at the P < 0.05 level) and 10 pairs of dizygotic twins (Z = 0.47; Z = 0.03, i.e., values not significant at the P < 0.05 level).
    NeuroImage 05/2000; 11(5 Pt 1):564-74. · 6.25 Impact Factor