New advances in computational modeling and instrumentation in the past decade has enabled the use of electromagnetic radiation for non-invasive monitoring of the physio-logical state of biological tissues. The near infrared (NIR) light having the wavelength range of 600 nm -1000 nm has been the main contender in these emerging molecular imaging modalities. Assessment of accurate pathological condition of the tissue under investigation relies on the contrast in the molecular images, where the endogenous contrast may not be sufficient in these scenarios. The fluorescence (exogenous) contrast agents have been deployed to overcome these difficulties, where the preferential uptake by the tumor vasculature leads to high contrast,making this modality one of the biggest contenders in small-animal and soft-tissue molecular imaging modalities. In Fluorescence diffuse optical spectroscopy/imaging, this exogenous drug is excited by NIR laser light causing the emission of the fluorescence light. The emitted fluorescence light is typically dependent on the life time and concentration of the exogenous drug coupled with physiology associated with the tissue under investigation. As there is an excitation and emission of the light,the underlying physics of the problem is described by a coupled diffusion equations. These coupled diffusion equations are typically solved by advanced numerical methods, which tend to be computationally demanding. In this work, analytical solutions for these coupled partial differential equations (PDEs) for the regular geometries for both time-domain and frequency-domain cases were developed. Till now, the existing literature has not dealt with all regular geometries and derived analytical solutions were only for couple of geometries. Here a universally acceptable generic solution was developed based on Green’s function approach that is applicable to any regular geometry. Using this, the analytical solutions for the regular geometries that is encountered in diffuse fluorescence spectroscopy/imaging were obtained. These solutions can play an important role in determining the bulk fluorescence properties of the tissue, which could act as good initial guesses for the advanced image reconstruction techniques and/or can also facilitate the calibration of experimental fluorescence data by removing biases and source-detector variations. In the second part of this work, the developed analytical models for regular geometries were validated through comparison with the established numerical models that are traditionally used in the diffuse fluorescence spectroscopy/imaging. This comparison not only validated the developed analytical models, but also showed that analytical models are capable of providing bulk fluorescence properties with at least one order of magnitude less computational cost compared to the highly optimized traditional numerical models.

Epileptic syndromes with continuous spikes and waves during slow sleep (CSWS) are age-related epileptic encephalopathy characterized by the development of various psychomotor regressions in close temporal concordance with the appearance of the electroencephalogram (EEG) pattern of CSWS (Tassinari et al. 2000). This EEG pattern consists in sleep-related activation and diffusion of spike-wave discharges during usually more than 85% of non-rapid eye movement (non-REM) sleep (Tassinari et al. 2000). <p>A minority of the CSWS cases has been associated to cortical or thalamic lesions (symptomatic cases), while in the other cases, the aetiology is unknown. We reported two families combining benign childhood epilepsy with centro-temporal spikes (BCECS), which is the most common form of idiopathic epilepsy in childhood, and cryptogenic epilepsy with CSWS in first-degree relatives. As idiopathic epilepsies are by definition epilepsies related to a genetic predisposition, these data suggests the existence of a continuum ranging from asymptomatic carriers of centro-temporal spikes to cryptogenic epilepsies with CSWS. This hypothesis is further supported by common clinical characteristics between BCECS and epilepsies with CSWS (Fejerman et al. 2000).<p>Epileptic syndromes with CSWS are characterized by an acute phase defined by the emergence of psychomotor deficits, various types of seizures and CSWS activity at around three to eight years of age (Holmes and Lenck-Santini, 2006; Veggiotti et al. 2001). This acute phase is followed by a recovery phase in which patients’ clinical condition improves together with the remission of CSWS pattern, which spontaneously occur at around 15 years of age but may be prompted by using antiepileptic drugs (AED) including corticosteroids (Holmes and Lenck-Santini, 2006; Veggiotti et al. 2001). This biphasic evolution suggests that CSWS activity largely contributes to the psychomotor deficits observed in these patients (Holmes and Lenck-Santini, 2006; Van Bogaert et al. 2006). However, some authors still consider CSWS activity as an epiphenomenon reflecting the underlying brain pathology, rather than the direct cause of the psychomotor regression (Aldenkamp and Arends, 2004). The pathophysiological mechanisms of how CSWS activity could actually lead to psychomotor regression are still poorly understood.<p>Functional cerebral imaging techniques such as positron emission tomography (PET) or functional magnetic resonance imaging (fMRI), represent unique ways to non-invasively study the impact of epileptic activity on normal brain function. The PET technique using [18F]-fluorodeoxyglucose (FDG) gives information about the regional neuronal glucose consumption via the neurometabolic coupling while the fMRI technique studies the regional perfusional changes directly related to specific events of interest via the neurovascular coupling. We applied both FDG-PET and EEG combined with fMRI (EEG-fMRI) techniques to epileptic children with CSWS to better approach the functional repercussions of CSWS activity on neurophysiological functions and to determine the potential pathophysiological link between CSWS activity and psychomotor regression.<p>In a first FDG-PET study, we determined the regional cerebral glucose metabolic patterns at the acute phase of CSWS in 18 children. We found three types of metabolic patterns: the association of focal hypermetabolism with distinct hypometabolism in 10 patients, focal hypometabolism without any associated area of increased metabolism in five children, and the absence of any significant metabolic abnormality in three patients. The hypermetabolic brain areas were anatomically related to an EEG focus. This anatomical relationship was clearly less consistent for hypometabolic regions. The metabolic abnormalities involved mainly the associative cortices. The metabolic heterogeneity found in these children could be due to the use of corticosteroids before PET as it was significantly associated with the absence of focal hypermetabolism. At the group level, patients with at least one hypermetabolic brain areas showed significant increased metabolism in the right parietal region that was associated to significant hypometabolism in the prefrontal cortex. This finding was interpreted as a phenomenon of remote inhibition of the frontal lobes by highly epileptogenic and hypermetabolic posterior cortex. This hypothesis was supported by effective connectivity analyses which demonstrated the existence of significant changes in the metabolic relationship between these brain areas in this group of children compared to the control group or to the group of children without any significant hypermetabolic brain area. <p>This remote inhibition hypothesis would be reinforced by the demonstration, at the recovery phase of CSWS, of a common resolution of hypermetabolism at the site of epileptic foci and hypometabolism in distant connected brain areas. We thus performed a second FDG-PET study to determine the evolution of cerebral metabolism in nine children recovering from CSWS. At the acute phase of CSWS, all children had a metabolic pattern characterized by the association of focal hypermetabolism with distinct focal hypometabolic areas. The evolution to CSWS recovery was characterized by a complete or almost complete regression of both hypermetabolic and hypometabolic abnormalities. At the group level, the altered effective connectivity found at the acute phase between focal hypermetabolism (centro-parietal regions and right fusiform gyrus) and widespread hypometabolism (prefrontal and orbito-frontal cortices, temporal lobes, left parietal cortex, precuneus and cerebellum) markedly regressed at recovery. These results were of particular interest because they strongly suggested that the metabolic abnormalities observed during the acute phase of CSWS were mainly related to the neurophysiological effects of CSWS activity and not to the underlying cause of the epileptic disease. Moreover, this study confirmed that phenomena of remote inhibition do occur in epileptic syndromes with CSWS. <p>EEG-fMRI is a functional cerebral imaging technique that allows non-invasive mapping of haemodynamic changes directly associated to epileptic activity. In a first EEG-fMRI study, we determined the clinical relevance of the perfusional changes linked to interictal epileptic discharges in a group of seven children with pharmacoresistant focal epilepsy. This study showed that the EEG-fMRI technique is a promising tool to non-invasively localize the epileptic focus and its repercussion on normal brain function in children with epilepsy. Then, to further demonstrate the involvement of CSWS activity in the neurophysiological changes detected by FDG-PET, we used the EEG-fMRI technique to study the perfusional changes directly related to the epileptic activity in an epileptic girl with CSWS. This patient developed a cognitive and behavioural regression in association with a major increase in frequency and diffusion of the spike-wave discharges during the awake state (spike index: 50-75%) and non-REM sleep (spike index: 85-90%). The patient’s neuropsychological profile was dominated by executive dysfunction and memory impairment. During runs of secondarily generalized spike-wave discharges, EEG-fMRI demonstrated deactivations in the lateral and medial fronto-parietal cortices, posterior cingulate gyrus and cerebellum together with focal relative activations in the right frontal, parietal and temporal cortices. These results suggested that the neuropsychological impairment in this case could be related to specific cortical dysfunction secondary to the spread of the epileptic activity from focal hypermetabolic foci. <p>Taken together, both FDG-PET and EEG-fMRI investigations performed in epileptic children with CSWS have shown increases in metabolism/perfusion at the site of the epileptic focus that were associated to decreases in metabolism/perfusion in distinct connected brain areas. These data highly suggest that the neurophysiological effects of CSWS activity are not restricted to the epileptic focus but spread to connected brain areas via a possible mechanism of surrounding and/or remote inhibition. This mechanism is characterised by an epilepsy-induced inhibition of neurons that surround or are remote from the epileptic focus and connected with it via cortico-cortical or polysynaptic pathways (Witte and Bruehl, 1999). The existence of surrounding and remote inhibition phenomena have been well documented in different types of animal models of focal epilepsy using various functional cerebral imaging methods such as autoradiography or optical imaging (Bruehl et al. 1998; Bruehl and Witte, 1995; Witte et al. 1994). Their occurrence in human epilepsy have also been suspected in temporal or extra-temporal lobe epilepsies using FDG-PET, EEG-fMRI or single photon emission computed tomography (SPECT) (Blumenfeld et al. 2004; Schwartz and Bonhoeffer, 2001; Van Paesschen et al. 2003; Van Paesschen et al. 2007). Moreover, the demonstration of the regression of distant hypometabolic areas after surgical resection or disconnection of the epileptic focus further suggest that such inhibition mechanism do occur in epilepsy (Bruehl et al. 1998; Jokeit et al. 1997). On a clinical point of view, the demonstration of the existence of such inhibition mechanisms in epilepsies with CSWS brings new important insights for the understanding of the pathophysiological mechanisms involved in the psychomotor regression observed in these conditions. Indeed, these data highly suggest that the psychomotor regression is not only related to the neurophysiological impairment at the site of the epileptic foci but also to epilepsy-induced neurophysiological changes in distant connected brain areas. <p><p> / Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished

L’accident vasculaire cérébrale (AVC) ischémique est une des premières causes de mortalité dans le monde, par conséquent il constitue un véritable enjeu de santé publique. Cette pathologie résulte de l’obstruction d’une artère cérébrale par un caillot et déclenche une inflammation, pouvant majorer les lésions tissulaires du cerveau. À ce jour les traitements anti-inflammatoires appliqués en clinique se sont révélés inefficaces. Il est donc indispensable de développer de nouvelles approches diagnostiques pour une meilleure compréhension des mécanismes biologiques impliqués dans cette pathologie. Dans ce contexte, nous avons proposé la conception d’une nanoplateforme hybride multimodale comme agent de contraste adapté à trois techniques d’imagerie médicale. Ces nanoparticules au cœur inorganique, composé de GdF3 augmentent sensiblement le contraste en IRM et leur opacité procure un rehaussement de contraste pour le Scanner Spectral à Comptage Photonique (SPCCT), une technique de développement récent. La troisième modalité, la microscopie biphotonique procure une haute résolution et une très grande sensibilité, tout en permettant d’obtenir des images en temps réel. Grâce à un chromophore adapté, greffé à la surface de la particule, cette modalité devient également accessible. Ces particules inorganiques sont synthétisées par une méthode solvothermale originale, développée par notre équipe. La surface des nanoparticules est ensuite modifiée par différents ligands polyéthylène glycol (PEG) fonctionnalisés, qui rendent les particules de GdF3 stables en milieu physiologique (comme le sang), biocompatibles et furtives. Enfin, un chromophore spécialement développé au sein de notre laboratoire, pour des applications d’absorption biphotonique, a été greffé à la surface de la particule. Le couplage du chromophore a été effectué via une réaction click azoture-alcyne, activée thermiquement (sans catalyse par Cu(I)). La toxicité des particules a été évaluée par deux techniques différentes, appliquées sur des cellules d’origine humaine. À l’issue de ces tests aucun effet cytotoxique n’a été observé. Après avoir démontré les propriétés multimodales de ces nanoobjets, des expériences précliniques in vivo ont été menées. Nous avons montré, que lors de l’observation du cerveau de souris la nanosonde augmente efficacement le contraste en SPCCT, IRM et produit un signal intense en microscopie 2-photons intravitale. Les particules se sont révélées particulièrement stables dans le sang : grâce à leur furtivité elles restent dans la circulation longtemps, ce qui favorise leur passage à travers la barrière hémato-enchéphalique lésée. Elles sont également phagocytées par les cellules immunitaires activées. La dynamique spatio-temporelle de ces cellules marquées par les nanoparticules a pu être imagée / Ischemic stroke, as one of the most common causes of death, represents an important health issue. The pathology consists of the occlusion of an artery in the brain leading to an acute inflammatory process. Post-stroke inflammation usually results in irreversible secondary brain tissue damage. To date, the clinical application of anti-inflammatory treatments has been either negative or inconclusive. For a better understanding of this complex physiological process and development of efficient treatment, there is an urgent need to develop performant in-vivo diagnostic tools. In that context, we proposed to design a multimodal hybrid nanoprobe for enhancing the contrast in three different clinical and pre-clinical imaging modalities. The ability of this probe to enhance contrast in MRI (Magnetic Resonance Imaging) and a recently developed spectral photon counting scanner computed tomography (SPCCT) is intrinsic to the inorganic GdF3 core. The inorganic nanoparticle size and morphology was optimized for the biological application. The third modality, two-photon imaging, provides high spatial resolution, high sensitivity, and allows real-time imaging. To make GdF3 nanoparticles visible by two-photon microscopy, a specially designed organic moiety is added to the nanoplatform. The inorganic nanoparticles are synthesized by the original solvothermal method developed in our group. Surface modifications with different PEG derivatives confer to the GdF3 nanoparticles high stability in physiological media (such as blood), biocompatibility, and stealth. The two-photon active chromophore synthesized in our laboratory is grafted to the particle surface via a thermally activated (catalyst-free) alkyne-azide click reaction. Toxicity of the nanoobjects has been assessed by using two different tests on four human-derived cells, and no cytotoxic effect of the particles was found. After the demonstration of the multimodality of the particles, pre-clinical in vivo experiments were performed. We evidenced that the particles successfully enhance SPCCT, MRI contrast in the brain of the small animal via a T2-effect and provide a high-intensity two-photon signal for in-vivo microscopy. Besides, the nanoparticles revealed to be stable and long-circulating in the blood, which favored their cross through the altered blood-brain barrier. Their phagocytose by activated immune cells offered the possibility to follow cell-trafficking

Die Autoimmunenzephalitis ist eine kürzlich beschriebene entzündliche Erkrankung des zentralen Nervensystems, die Gedächtnisdefizite, Psychosen, oder epileptische Anfälle hervorrufen kann. Derzeit ist hingegen noch nicht ausreichend verstanden, welche pathologischen Veränderungen zu den kognitiven Defiziten führen und welche neuropsychologischen und bildgebenden Langzeitoutcomes zu erwarten sind. Anhand von strukturellen und funktionellen Bildgebungsanalysen zeigt diese Dissertation, dass kognitive Defizite auch nach der akuten Phase der Autoimmunenzephalitis fortbestehen können. Bei der LGI1-Enzephalitis gehen Gedächtnisdefizite mit fokalen strukturellen Läsionen im Hippocampus einher. Durch eine funktionelle Störung der Resting-State-Konnektivität des Default-Mode- und Salienznetzwerkes beeinträchtigen diese Hippocampusläsionen auch Hirnregionen außerhalb des limbischen Systems. Bei Patient:innen mit NMDA-Rezeptor-Enzephalitis finden sich in der longitudinalen neuropsychologischen Untersuchung trotz guter allgemeiner Genesung auch noch mehrere Jahre nach der Akutphase persistierende Defizite des Gedächtnisses und exekutiver Funktionen. Zuletzt zeigt eine transdiagnostische Analyse, dass der anteriore Hippocampus eine erhöhte Vulnerabilität gegenüber immunvermittelten pathologischen Prozessen aufweist. Diese Ergebnisse legen nahe, dass kognitive Symptome auch noch nach der Entlassung aus der stationären Behandlung fortbestehen können. Sowohl umschriebene strukturelle Hippocampusläsionen als auch Veränderungen in makroskopischen funktionellen Hirnnetzwerken tragen zur pathophysiologischen Erklärung dieser Symptome bei. Zudem erlauben diese Ergebnisse einen Einblick in neuroplastische Veränderungen des Gehirns und haben weitreichende Implikationen für die Langzeitversorgung und das Design zukünftiger klinischer Studien. / Autoimmune encephalitis is a recently described inflammatory disease of the central nervous system that can cause memory deficits, psychosis, or seizures. The trajectory of cognitive dysfunction and the underlying long-term imaging correlates are, however, not yet fully understood. By using advanced structural and functional neuroimaging, this thesis shows that cognitive deficits persist beyond the acute phase. In LGI1 encephalitis, MRI postprocessing revealed that memory deficits are related to focal structural hippocampal lesions. These hippocampal lesions propagate to brain areas outside the limbic system through aberrant resting-state connectivity of the default mode network (DMN) and the salience network. In NMDA receptor encephalitis, a longitudinal analysis of neuropsychological data describes persistent cognitive deficits, especially in the memory and executive domains, despite good physical recovery several years after the acute disease. Lastly, a transdiagnostic analysis reveals that the anterior hippocampus is particularly vulnerable to immune-mediated damage. In conclusion, these results demonstrate that cognitive symptoms in autoimmune encephalitis can persist beyond discharge from neurological care. Both discrete structural hippocampal damage and changes in macroscopic functional networks shed light on the pathophysiological basis of these symptoms. These findings help to explain how the brain responds to pathological damage and have substantial implications for long-term patient care and the design of future clinical studies.