Mélanie Pélégrini-Issac

Polytech Paris-UPMC, Lutetia Parisorum, Île-de-France, France

Are you Mélanie Pélégrini-Issac?

Claim your profile

Publications (84)228.33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Severe traumatic brain injury (TBI) is characterized mainly by diffuse axonal injuries (DAI).The cortico-subcortical disconnections induced by such fiber disruption play a central role in consciousness recovery. We hypothesized that these cortico-subcortical deafferentations inferred from diffusion MRI data could differentiate between TBI patients with favorable or unfavorable (death, vegetative state, or minimally conscious state) outcome one year after injury.
    Journal of Neuroradiology 06/2014; · 1.24 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Functional brain networks are sets of cortical, subcortical and cerebellar regions whose neuronal activities are synchronous over multiple time scales. Spatial independent component analysis (sICA) is a widespread approach to identify functional networks in the human brain from functional magnetic resonance imaging (fMRI) resting-state data, and there is now a general agreement regarding the cortical regions involved in each network. It is well known that these cortical regions are preferentially connected with specific subcortical functional territories, however subcortical components have not been observed whether in a robust or in a reproducible manner using sICA. This article presents a new method to analyze resting-state fMRI data that allows for robust and reproducible association of subcortical regions with well-known patterns of cortical regions. The approach relies on the hypothesis that the time course in subcortical regions is similar to that in cortical regions belonging to the same network. First, sICA followed by hierarchical clustering is performed on cortical time series to extract group functional cortical networks. Secondly, these networks are complemented with related subcortical areas based on the similarity of their time courses, using an individual general linear model and a random-effect group analysis. Two independent resting-state fMRI datasets were processed and the subcortical components of both datasets overlapped by up to 99% depending on the network, showing the reproducibility and the robustness of our approach. The relationship between subcortical components and functional cortical networks was consistent with functional territories (sensorimotor, associative and limbic) from an immunohistochemical atlas of the basal ganglia.
    Brain connectivity. 02/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To validate semiautomated spinal cord segmentation in healthy subjects and patients with neurodegenerative diseases and trauma. Forty-nine healthy subjects, as well as 29 patients with amyotrophic lateral sclerosis, 19 with spinal muscular atrophy, and 14 with spinal cord injuries were studied. Cord area was measured from T2 -weighted 3D turbo spin echo images (cord levels from C2 to T9) using the semiautomated segmentation method of Losseff et al (Brain [1996] 119(Pt 3):701-708), compared with manual segmentation. Reproducibility was evaluated using the inter- and intraobserver coefficient of variation (CoV). Accuracy was assessed using the Dice similarity coefficient (DSC). Robustness to initialization was assessed by simulating modifications to the contours drawn manually prior to segmentation. Mean interobserver CoV was 4.00% for manual segmentation (1.90% for Losseff's method) in the cervical region and 5.62% (respectively 2.19%) in the thoracic region. Mean intraobserver CoV was 2.34% for manual segmentation (1.08% for Losseff's method) in the cervical region and 2.35% (respectively 1.34%) in the thoracic region. DSC was high (0.96) in both cervical and thoracic regions. DSC remained higher than 0.8 even when modifying initial contours by 50%. The semiautomated segmentation method showed high reproducibility and accuracy in measuring spinal cord area. J. Magn. Reson. Imaging 2014. © 2014 Wiley Periodicals, Inc.
    Journal of Magnetic Resonance Imaging 01/2014; · 2.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To evaluate multimodal MRI of the spinal cord in predicting disease progression and one-year clinical status in amyotrophic lateral sclerosis (ALS) patients. After a first MRI (MRI1), 29 ALS patients were clinically followed during 12 months; 14/29 patients underwent a second MRI (MRI2) at 11±3 months. Cross-sectional area (CSA) that has been shown to be a marker of lower motor neuron degeneration was measured in cervical and upper thoracic spinal cord from T2-weighted images. Fractional anisotropy (FA), axial/radial/mean diffusivities (λ⊥, λ//, MD) and magnetization transfer ratio (MTR) were measured within the lateral corticospinal tract in the cervical region. Imaging metrics were compared with clinical scales: Revised ALS Functional Rating Scale (ALSFRS-R) and manual muscle testing (MMT) score. At MRI1, CSA correlated significantly (P<0.05) with MMT and arm ALSFRS-R scores. FA correlated significantly with leg ALFSRS-R scores. One year after MRI1, CSA predicted (P<0.01) arm ALSFSR-R subscore and FA predicted (P<0.01) leg ALSFRS-R subscore. From MRI1 to MRI2, significant changes (P<0.01) were detected for CSA and MTR. CSA rate of change (i.e. atrophy) highly correlated (P<0.01) with arm ALSFRS-R and arm MMT subscores rate of change. Atrophy and DTI metrics predicted ALS disease progression. Cord atrophy was a better biomarker of disease progression than diffusion and MTR. Our study suggests that multimodal MRI could provide surrogate markers of ALS that may help monitoring the effect of disease-modifying drugs.
    PLoS ONE 01/2014; 9(4):e95516. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Post-concussion syndrome has been related to axonal damage in patients with mild traumatic brain injury, but little is known about the consequences of injury on brain networks. In the present study, our aim was to characterize changes in functional brain networks following mild traumatic brain injury in patients with post-concussion syndrome using resting-state functional magnetic resonance imaging data. We investigated 17 injured patients with persistent post-concussion syndrome (under the DSM-IV criteria) at 6 months post-injury compared with 38 mild traumatic brain injury patients with no post-concussion syndrome and 34 healthy controls. All patients underwent magnetic resonance imaging examinations at the subacute (1-3 weeks) and late (6 months) phases after injury. Group-wise differences in functional brain networks were analyzed using graph theory measures. Patterns of long-range functional networks alterations were found in all mild traumatic brain injury patients. Mild traumatic brain injury patients with post-concussion syndrome had greater alterations than patients without post-concussion syndrome. In patients with post-concussion syndrome, changes specifically affected temporal and thalamic regions predominantly at the subacute stage and frontal regions at the late phase. Our results suggest that the post-concussion syndrome is associated with specific abnormalities in functional brain network that may contribute to explain deficits typically observed in PCS patients.
    PLoS ONE 10/2013; 8(6):e65470. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The presence of a postconcussion syndrome (PCS) induces substantial socio-professional troubles in mild traumatic brain injury (mTBI) patients. Although the exact origin of these disorders is not known, they may be the consequence of diffuse axonal injury (DAI) impacting structural integrity. In the present study, we compared structural integrity at the subacute and late stages after mTBI and in case of PCS, using diffusion-weighted imaging (DWI). Fifty-three mTBI patients were investigated and compared with 40 healthy controls. All patients underwent a DWI examination at the subacute (8-21 days) and late (6 months) phases after injury. MTBI patients with PCS were detected at the subacute phase using the ICD-10 classification. Groupwise differences in structural integrity were investigated using Tract-Based Spatial Statistics (TBSS). A loss of structural integrity was found in mTBI patients at the subacute phase but partially resolved over time. Moreover, we observed that mTBI patients with PCS had greater and wider structural impairment than patients without PCS. These damages persisted over time for PCS patients, while mTBI patients without PCS partly recovered. In conclusion, our results strengthen the relationship between structural integrity and PCS.
    Brain Imaging and Behavior 04/2012; 6(2):283-92. · 2.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Consciousness is reduced during nonrapid eye movement (NREM) sleep due to changes in brain function that are still poorly understood. Here, we tested the hypothesis that impaired consciousness during NREM sleep is associated with an increased modularity of brain activity. Cerebral connectivity was quantified in resting-state functional magnetic resonance imaging times series acquired in 13 healthy volunteers during wakefulness and NREM sleep. The analysis revealed a modification of the hierarchical organization of large-scale networks into smaller independent modules during NREM sleep, independently from EEG markers of the slow oscillation. Such modifications in brain connectivity, possibly driven by sleep ultraslow oscillations, could hinder the brain's ability to integrate information and account for decreased consciousness during NREM sleep.
    Proceedings of the National Academy of Sciences 03/2012; 109(15):5856-61. · 9.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gilles de la Tourette syndrome is a clinically heterogeneous disorder with poor known pathophysiology. Recent neuropathological and structural neuroimaging data pointed to the dysfunction of cortico-basal ganglia networks. Nonetheless, it is not clear how these structural changes alter the functional activity of the brain and lead to heterogeneous clinical expressions of the syndrome. The objective of this study was to evaluate global integrative state and organization of functional connections of sensori-motor, associative and limbic cortico-basal ganglia networks, which are likely involved in tics and behavioural expressions of Gilles de la Tourette syndrome. We also tested the hypothesis that specific regions and networks contribute to different symptoms. Data were acquired on 59 adult patients and 27 gender- and age-matched controls using a 3T magnetic resonance imaging scanner. Cortico-basal ganglia networks were constructed from 91 regions of interest. Functional connectivity was quantified using global integration and graph theory measures. We found a stronger functional integration (more interactions among anatomical regions) and a global functional disorganization of cortico-basal ganglia networks in patients with Gilles de la Tourette syndrome compared with controls. All networks were characterized by a shorter path length, a higher number of and stronger functional connections among the regions and by a loss of pivotal regions of information transfer (hubs). The functional abnormalities correlated to tic severity in all cortico-basal ganglia networks, namely in premotor, sensori-motor, parietal and cingulate cortices and medial thalamus. Tic complexity was correlated to functional abnormalities in sensori-motor and associative networks, namely in insula and putamen. Severity of obsessive-compulsive disorder was correlated with functional abnormalities in associative and limbic networks, namely in orbito-frontal and prefrontal dorsolateral cortices. The results suggest that the pattern of functional changes in cortico-basal ganglia networks in patients could reflect a defect in brain maturation. They also support the hypothesis that distinct regions of cortico-basal ganglia networks contribute to the clinical heterogeneity of this syndrome.
    Brain 03/2012; 135(Pt 6):1937-46. · 10.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Near infrared spectroscopy (NIRS) is a functional imaging technique allowing measurement of local cerebral oxygenation. This modality is particularly adapted to critically ill neonates, as it can be used at the bedside and is a suitable and noninvasive tool for carrying out longitudinal studies. However, NIRS is sensitive to the imaged medium and consequently to the optical properties of biological tissues in which photons propagate. In this study, the effect of the neonatal fontanel was investigated by predicting photon propagation using a probabilistic Monte Carlo approach. Two anatomical newborn head models were created from computed tomography and magnetic resonance images: (1) a realistic model including the fontanel tissue and (2) a model in which the fontanel was replaced by skull tissue. Quantitative change in absorption due to simulated activation was compared for the two models for specific regions of activation and optical arrays simulated in the temporal area. A correction factor was computed to quantify the effect of the fontanel and defined by the ratio between the true and recovered change. The results show that recovered changes in absorption were more precise when determined with the anatomical model including the fontanel. The results suggest that the fontanel should be taken into account in quantification of NIRS responses to avoid misinterpretation in experiments involving temporal areas, such as language or auditory studies. Hum Brain Mapp, 2011. © 2011 Wiley Periodicals, Inc.
    Human Brain Mapping 11/2011; · 6.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Consciousness has been related to the amount of integrated information that the brain is able to generate. In this paper, we tested the hypothesis that the loss of consciousness caused by propofol anesthesia is associated with a significant reduction in the capacity of the brain to integrate information. To assess the functional structure of the whole brain, functional integration and partial correlations were computed from fMRI data acquired from 18 healthy volunteers during resting wakefulness and propofol-induced deep sedation. Total integration was significantly reduced from wakefulness to deep sedation in the whole brain as well as within and between its constituent networks (or systems). Integration was systematically reduced within each system (i.e., brain or networks), as well as between networks. However, the ventral attentional network maintained interactions with most other networks during deep sedation. Partial correlations further suggested that functional connectivity was particularly affected between parietal areas and frontal or temporal regions during deep sedation. Our findings suggest that the breakdown in brain integration is the neural correlate of the loss of consciousness induced by propofol. They stress the important role played by parietal and frontal areas in the generation of consciousness.
    NeuroImage 07/2011; 57(1):198-205. · 6.25 Impact Factor
  • Source
    Organization for Human Brain(OHB'11); 06/2011
  • Source
    Computer Assisted Radiology and Surgery(CARS'11); 06/2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Mild traumatic brain injury (mTBI) can induce long-term behavioral and cognitive disorders. Although the exact origin of these mTBI-related disorders is not known, they may be the consequence of diffuse axonal injury (DAI). Here, we investigated whether MRI at the subacute stage can detect lesions that are associated with poor functional outcome in mTBI by using anatomical images (T(1) ) and diffusion tensor imaging (DTI). Twenty-three patients with mTBI were investigated and compared with 23 healthy volunteers. All patients underwent an MRI investigation and clinical tests between 7 and 28 days (D15) and between 3 and 4 months (M3) after injury. Patients were divided in two groups of poor outcome (PO) and good outcome (GO), based on their complaints at M3. Groupwise differences in gray matter partial volume between PO patients, GO patients and controls were analyzed using Voxel-Based Morphometry (VBM) from T(1) data at D15. Differences in microstructural architecture were investigated using Tract-Based Spatial Statistics (TBSS) and the diffusion images obtained from DTI data at D15. Permutation-based non-parametric testing was used to assess cluster significance at p < 0.05, corrected for multiple comparisons. Twelve GO patients and 11 PO patients were identified on the basis of their complaints. In PO patients, gray matter partial volume was significantly lower in several cortical and subcortical regions compared with controls, but did not differ from that of GO patients. No difference in diffusion variables was found between GO and controls. PO patients showed significantly higher mean diffusivity values than both controls and GO patients in the corpus callosum, the right anterior thalamic radiations and the superior longitudinal fasciculus, the inferior longitudinal fasciculus and the fronto-occipital fasciculus bilaterally. In conclusion, PO patients differed from GO patients by the presence of diffusion changes in long association white matter fiber tracts but not by gray matter partial volume. These results suggest that DTI at the subacute stage may be a predictive marker of poor outcome in mTBI.
    Human Brain Mapping 06/2011; 32(6):999-1011. · 6.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gonadotropin-releasing hormone (GnRH) agonists, such as leuprorelin, are recommended in the patients with pedophilia at highest risk of offending. However, the cerebral mechanisms of the effects of these testosterone-decreasing drugs are poorly known. This study aimed to identify changes caused by leuprorelin in a pedophilic patient's brain responses to pictures representing children. Clinical, endocrine, and fMRI investigations were done of a man with pedophilia before leuprorelin therapy and 5 months into leuprorelin therapy. Patient was compared with an age-matched healthy control also assessed 5 months apart. Before therapy, pictures of boys elicited activation in the left calcarine fissure, left insula, anterior cingulate cortex, and left cerebellar vermis. Five months into therapy, all the above-mentioned activations had disappeared. No such activations and, consequently, no such decreases occurred in the healthy control. The results of this pilot study suggest that leuprorelin decreased activity in regions known to mediate the perceptual, motivational, and affective responses to visual sexual stimuli.
    International Journal of Offender Therapy and Comparative Criminology 04/2011; 56(1):50-60. · 0.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Diffuse optical imaging (DOI) is a non invasive technique allowing the recovery of hemodynamic changes in the brain. Due to the diffusive nature of photon propagation in turbid media and the fact that cerebral tissues are located around 1.5 cm under the adult human scalp, DOI measurements are subject to partial volume errors. DOI measurements are also sensitive to large pial vessels because oxygenated and deoxygenated hemoglobin are the dominant chromophores in the near infrared window. In this study, the effect of the extra-cerebral vasculature in proximity of the sagittal sinus was investigated for its impact on DOI measurements simulated over the human adult visual cortex. Numerical Monte Carlo simulations were performed on two specific models of the human head derived from magnetic resonance imaging (MRI) scans. The first model included the extra-cerebral vasculature in which constant hemoglobin concentrations were assumed while the second did not. The screening effect of the vasculature was quantified by comparing recovered hemoglobin changes from each model for different optical arrays and regions of activation. A correction factor accounting for the difference between the recovered and the simulated hemoglobin changes was computed in each case. The results show that changes in hemoglobin concentration are better estimated when the extra-cerebral vasculature is modeled and the correction factors obtained in this case were at least 1.4-fold lower. The effect of the vasculature was also examined in a high-density diffuse optical tomography configuration. In this case, the difference between changes in hemoglobin concentration recovered with each model was reduced down to 10%.
    Biomedical Optics Express 01/2011; 2(3):680-95. · 3.18 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A low-cost device using diffuse optical imaging (DOI) for measuring in vivo hemodynamic changes in the spinal cord has been developed. The proposed system is aimed at monitoring for the first time real-time hemodynamic changes associated with intraspinal rhythmic motor activity monitored by electroneurogram (ENG) evoked in paralyzed cats (fictive locomotion). The device contains the emitting and collecting probes within a saddle that fits over a vertebra and has been developed with discrete component circuits. Experiments performed in two acutely decerebrate and paralyzed cats confirm a noticeable and reproducible hemodynamic response during episodes of fictive locomotion. The device is designed so that it could be implanted chronically. In the future, a multi-implant imaging platform could measure long-term hemodynamic changes in the spinal cord.
    IEEE Transactions on Biomedical Circuits and Systems 11/2010; · 2.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: During smooth pursuit, the image of the target is stabilized on the fovea, implying that speed judgments made during pursuit must rely on an extraretinal signal providing precise eye speed information. To characterize the introduction of such extraretinal signal into the human visual system, we performed a factorial, functional magnetic resonance imaging experiment, in which we manipulated the factor eye movement, with "fixation" and "pursuit" as levels, and the factor task, with "speed" and "form" judgments as levels. We hypothesized that the extraretinal speed signal is reflected as an interaction between speed judgments and pursuit. Random effects analysis yielded an interaction only in dorsal early visual cortex. Retinotopic mapping localized this interaction on the horizontal meridian (HM) between dorsal areas visual 2 and 3 (V2/V3) at 1-2 degrees azimuth. This corresponded to the position the pursuit target would have reached, if moving retinotopically, at the time of the subject's speed judgment. Because the 2 V2/V3 HMs are redundant, both may be involved in speed judgments, the ventral one involving judgments based on retinal motion and the dorsal one judgments requiring an internal signal. These results indicate that an extraretinal speed signal is injected into early visual cortex during pursuit.
    Cerebral Cortex 09/2010; 20(9):2172-87. · 8.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: While the cortical components of functional networks detected by spatial independent component analysis (sICA) in functional magnetic resonance imaging (fMRI) have been reproducibly described in various While the cortical components of functional networks detected by spatial independent component analysis (sICA) in functional magnetic resonance imaging (fMRI) have been reproducibly described in various studies, little is known about their subcortical components. In this study, we propose a method that extracts cortico-subcortical networks from fMRI data by first detecting cortical networks with sICA and then by complementing them with subcortical components using multiple regression, at both the individual and the group levels.studies, little is known about their subcortical components. In this study, we propose a method that extracts cortico-subcortical networks from fMRI data by first detecting cortical networks with sICA and then by complementing them with subcortical components using multiple regression, at both the individual and the group levels.
    Biomedical Imaging: From Nano to Macro, 2010 IEEE International Symposium on; 05/2010
  • [Show abstract] [Hide abstract]
    ABSTRACT: We use Monte Carlo simulations to investigate the influence of the sagittal sinus vein on diffuse optical imaging measurements. Effects are characterized by quantitative additional partial volume errors computed with respect to a cerebral activation.
    04/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Grid technologies are appealing to deal with the challenges raised by computational neurosciences and support multi-centric brain studies. However, core grids middleware hardly cope with the complex neuroimaging data representation and multi-layer data federation needs. Moreover, legacy neuroscience environments need to be preserved and cannot be simply superseded by grid services. This paper describes the NeuroLOG platform design and implementation, shedding light on its Data Management Layer. It addresses the integration of brain image files, associated relational metadata and neuroscience semantic data in a heterogeneous distributed environment, integrating legacy data managers through a mediation layer.
    Studies in health technology and informatics 01/2010; 159:112-23.

Publication Stats

1k Citations
228.33 Total Impact Points

Institutions

  • 2005–2014
    • Polytech Paris-UPMC
      Lutetia Parisorum, Île-de-France, France
    • University of Minnesota Twin Cities
      • Department of Radiology
      Minneapolis, MN, United States
  • 2002–2014
    • Unité Inserm U1077
      Caen, Lower Normandy, France
    • Max Planck Institute for Human Cognitive and Brain Sciences
      • Department of Neurology
      Leipzig, Saxony, Germany
  • 2010–2013
    • Université Paris-Sud 11
      Orsay, Île-de-France, France
  • 2012
    • Hôpital La Pitié Salpêtrière (Groupe Hospitalier "La Pitié Salpêtrière - Charles Foix")
      Lutetia Parisorum, Île-de-France, France
  • 2011–2012
    • University of Liège
      • Cyclotron Research Centre
      Liège, WAL, Belgium
  • 2005–2012
    • French Institute of Health and Medical Research
      • Laboratory of Functional Imaging
      Paris, Ile-de-France, France
  • 2005–2009
    • Université de Montréal
      Montréal, Quebec, Canada
  • 2004–2008
    • Pierre and Marie Curie University - Paris 6
      Lutetia Parisorum, Île-de-France, France
  • 2005–2007
    • University College London
      • Wellcome Department of Imaging Neuroscience
      London, ENG, United Kingdom