Développement et application de l'imagerie quantitative du débit sanguin cérébral pour l'étude de modèles de l'obésité

par Haleh Soleimanzad

Projet de thèse en Imagerie et physique médicale

Sous la direction de Frédéric Pain et de Hirac Gurden.

Thèses en préparation à Paris Saclay , dans le cadre de Electrical,Optical,Bio: PHYSICS_AND_ENGINEERING , en partenariat avec Cnrs UMR 8165 - Imagerie et Modélisation en Neurobiologie et Cancérologie (IMNC) (laboratoire) , Imagerie Biophotonique In Vivo (equipe de recherche) et de Université Paris-Sud (établissement de préparation de la thèse) depuis le 01-10-2015 .

  • Résumé

    Développement et application de l'imagerie quantitative du débit sanguin cérébral pour l'étude de modèles de l'obésité Mesure quantitative L'activité vasculaire est nécessaire pour subvenir aux besoins en énergie liées à l'activité cérébrale. Les effets vasculaires (débit, constriction, dilatation) sont complexes et nécessitent des études physiologiques in vivo approfondies. La description des phénomènes hémodynamiques cérébraux est également largement inexplorée en particulier pour les sujets obèses. Dans ce contexte, les objectifs de la thèse seront (i) de développer des systèmes d'imagerie du système hémodynamiques pour (ii) obtenir des données originales concernant le débit, la vasoconstriction et la vasodilatation dans le cerveau chez le rat sain ou obèse. Objectifs • Développer et caractériser deux modalités d'imagerie du débit sanguin cérébral quantitatives et complémentaires • Obtenir et analyser des données sur le débit sanguin dans le système nerveux central pour l'étude de l'obésité Encadrement Le doctorant sera encadré par Frédéric Pain (HDR, resp Euqipe Imagerie Biophotonique In Vivo) pour le développement des instruments et méthodes pour l'imagerie quantitative du débit sanguin cérébral. Pour l'application biomédicale et l'analyse des résultats biologiques le doctorant sera co-encadré par Hirac Gurden(HDR, Neurobiologiste, resp. Equipe Métabolisme Imagerie Olfaction UMR8251.

  • Titre traduit

    Development of multiscale imaging modalities of cerebral blood flow for the study of obesity models.

  • Résumé

    Vascular activity is necessary to bring suitable energy supply for neuronal activity in the brain. Vascular dynamics are complex and need to be further understood in a physiological context in vivo. Description of hemodynamics is also a goal in the pathological brain such as in obesity. In this context, the aim of the Ph-D project is to obtain multiscale data on blood flow, vasodilation and vasoconstriction during activation of rodents brain in normal and obese rodents. The Ph-D student will be co-supervised by a senior investigator (F. Pain) in instrumentation and a senior neurobiologist (H. Gurden). He will be in charge of the development and in vivo validation of several imaging set ups. The first is a macroscope system already in use in the IMNC lab that the Ph.D student would adapt to simultaneous laser speckle contrast (LSC) and Intrinsic Optical Signal Imaging (IOSI). LSC will allow mapping of blood flow changes at the brain surface, and IOSI in green light would allow following dilation and construction at the arteriole levels. To gain insight to the flow and velocity at the capillaries level, the student will implement in a second set up the imaging of individual red blood cells shadows in capillaries loaded with fluorescence, on the newly acquired two photon microscopy system in the IMNC lab (France Life Imaging National Network). LSC imaging relies on the imaging of speckle figures produced by tissues illuminated in coherent (laser) light. This speckle patterns are not fixed as would be observed on a static object but rather time-dependent. The LSC technique consists in quantifying the local speckle contrast. For a fixed imaging exposure time, faster pattern changes lead to lower speckle contrast. Therefore the technique allows to map local blood flow changes that affect the contrast (Boas et Dunn 2010; Jones et al. 2008). IOSI imaging is a well-established technique that relies on intrinsic reflectance changes following activation due to hemodynamic changes. The amount of reflected light decreases with local increase in blood volume and may increase or decrease due to changes in the oxygenation balance of hemoglobin (Gurden, Uchida, et Mainen 2006). The IMNC lab has developed a multispectral IOSI system that allows extracting the 2D maps of the relative changes in total blood volume, and oxy-hemoglobin and de-oxyhemoglobine.(Chery et al. 2011; Renaud et al. 2012). The development of simultaneous LSC and IOSI imaging will require adapting instrumentation and optical paths of the existing macroscope. LSC will involve a systematic evaluation of several instrumental parameters including the exposure time, lens numerical aperture, and parameters involved in the processing of the speckle images to produce contrast maps. Using a fast acquisition camera, a multi-exposure scheme will be implemented to extend the regime of validity of speckle measurements and correct for the static speckle contribution.(Kazmi, Balial, et Dunn 2014; Rice et al. 2013) The implementation of blood flow measurement at the capillaries level in vivo, using two photon imaging will require the student to develop the technique and the analysis of two photon images(Tiret et al. 2009) that will be acquired in the IMNC lab. Under the supervision of an expert neurophysiologist, the student will have the opportunity to develop skills in neurophysiological brain imaging. Brain activation will be studied by the olfactory activation using controlled odorants flux. The olfactory bulb is a major brain sensory structure in rodents and is well adapted to optical imaging of brain activation since the functional modules (called glomeruli) are relatively superficial, close to the brain surface. In addition, the stimulation is physiologically relevant and can be easily controlled. Since the IMNC lab has a great expertise in olfactory physiology (Pain et al., 2011) and the study of neuro-vascular coupling, the PhD project will further explore coupling mechanisms between sensory evoked-activity and vascular responses in the normal brain. Although impairments of brain function were reported in obese subjects and rodent models, mechanisms underlying such dysfunctions are unknown. Thus, whether the neuro-vascular during obesity is affected and could participate in this loss of function is crucial to determine. This PhD project will test if obesity affects activity-dependent vascular activity. The PhD will be co-supervised by a neuroscientist (Hirac Gurden) and an instrumentation scientist (Frédéric Pain). The project involves two complementary aspects that the Ph-D student would have in charge: - Instrumental and methodological developments This consists in building and characterization of the set ups, It includes the choice of the more appropriate instruments , parts and schemes ; the opto-mechanical construction; the characterization of the imaging performances on phantoms; the development of acquisition software using software such as Matlab, ImageJ, Micromanager or Labview - In vivo data acquisition and analysis on anesthetized rodents (normal or obese) in the context of olfactory stimulation. Altogether, this interdisciplinary PhD research work will consist in acquiring the skills for in vivo optical brain imaging in rodents using either wide field approaches (LSC, IOSI) or microscopy (two photon imaging) and in analyzing the data to obtain relevant biological data. The development of these new optical methodologies will provide exciting insides into the study of hemodynamics in the normal brain but also in the brain of obese rodents.