"Renal autoregulation stabilizes renal blood flow to protect the glomerular capillaries and maintain glomerular filtration rates through two mechanisms: tubuloglomerular feedback (TGF) and the myogenic response (MR). It is considered that the feedback mechanisms operate independently in each nephron (the functional unit of the kidney) within a kidney, but renal autoregulation dynamics can be coupled between vascular connected nephrons. It has also been shown that the mechanisms are time-varying and interact with each other. Understanding of the significance of such complex behavior has been limited by absence of techniques capable of monitoring renal flow signals among more than 2 or 3 nephrons simultaneously. The purpose of this thesis was to develop approaches to allow the identification and characterization of spatial and temporal properties of renal autoregulation dynamics. We present evidence that laser speckle perfusion imaging (LSPI) effectively captures renal autoregulation dynamics in perfusion signals across the renal cortex of anaesthetized rats and that spatial heterogeneity of the dynamics is present and can be investigated using LSPI. Next, we present a novel approach to segment LSPI of the renal surface into phase synchronized clusters representing areas with coupled renal autoregulation dynamics. Results are shown for the MR and demonstrate that when a signal is present phase synchronized regions can be identified. We then describe an approach to identify quadratic phase coupling between the TGF and MR mechanisms in time and space. Using this approach we can identify locations across the renal surface where both mechanisms are operating cooperatively. Finally, we show how synchronization between nephrons can be investigated in relation to renal autoregulation effectiveness by comparing phase synchronization estimates from LSPI with renal autoregulation system properties estimated from renal blood flow and blood pressure measurements. Overall, we have developed approaches to 1) capture renal autoregulation dynamics across the renal surface, 2) identify regions with phase synchronized renal autoregulation dynamics, 3) quantify the presence of the TGF-MR interaction across the renal surface, and 4) determine how the above vary over time. The described tools allow for investigations of the significance and mechanisms behind the complex spatial interactions and time-varying properties of renal autoregulation dynamics. "

It is well known now that there exists a coupling between functional brain activity and regional blood flow response in the somatosensory cortex and other cortical areas. Various modalities, including functional magnetic resonance imaging and optical imaging (intrinsic signals as well as fluorescence), have been developed in the past to map functional brain activity. The complexity and fundamental physical constraints of the instruments preclude functional imaging in awake, behaving small animals. This thesis presents the method of Laser Speckle Imaging (LSI) of brain with high spatial and temporal resolution, and potential for imaging awake and behaving animals. The method has the potential to map brain activation with high sensitivity and spatiotemporal resolution without using any exogenous contrast agents. In LSI, scattered laser light with different paths produces a random interference pattern known as speckle, fluctuations of which contain information about the motion of particles in the underlying medium. A post-processing step is needed to extract information out of the speckle images, two of which we introduce in details. Our first method is based on Laser speckle contrast analysis (LASCA), which has been demonstrated as a full-field method for imaging the cerebral blood flow (CBF). However, conventional LASCA is limited to extremely low dynamic range because of the ambient background field, dark current and anomalies in the circuits of CCD camera, which makes it difficult to analyze the spatiotemporal variabilities in CBF. In this study, we propose an enhanced laser speckle contrast analysis (eLASCA) method to improve the dynamic range of LASCA based on monotonic point transformation (MPT). In addition, eLASCA greatly improves the CBF visualization, which is very helpful in demonstrating the details of CBF change. Our second method involves the second order features (SOFs) of the image; they are derived from the cooccurrence matrix that in turn was calculated over the same spatial and temporal window than for the contrast. The image quality metrics - equivalent number of looks, entropy and objective quality – showed superior performance of the SOFs comparing to the contrast analysis. / --

The roles of the vascular architecture and blood flow in response to neurovascular diseases are important in predicting physiological outcomes. Observing these parameters chronically with optical imaging techniques provides insight into the neurovascular recovery process. We develop and deploy optical imaging systems for monitoring the progression of vascular structure, perfusion, and functional blood response after ischemic stroke in a chronic rodent model to observe vascular dynamics of the cortex under normal and diseased pathologies. Specifically, we monitor the progression of the vascular structure and cerebral blood flow (CBF) over a chronic period in the rodent cortex after photo-thrombotic occlusion. Multi-Exposure Speckle Imaging (MESI) provides surface measurements of microvascular flow dynamics while Two-Photon Fluorescence Microscopy offers direct visualization of the microvascular structure. We observe the occurrence of vascular reorientation in the sub-surface microvascular structure over a 35 day post-occlusion period. We also correlate MESI flow estimates in the parenchyma with sub-surface microvascular volume fractions from two-photon microscopy to assess how vascular density influences the surface-integrated MESI measurements. Next, we develop and validate a MESI technique for measuring absolute changes of the functional blood flow response to forepaw stimulation in rodents, termed FA MESI. The optimal camera exposures for capturing the CBF response to forepaw stimulation are extracted from a training set of animal data and the feasibility of the technique is demonstrated in a testing animal set by comparing functional response results between new and existing techniques. We then deploy this system in a chronic study monitoring the progression of hemodynamic parameters after ischemic stroke within the functionally responding area of the cortex. The progression of the regional CBF perfusion and absolute changes in the magnitude of the functional blood flow response are monitored chronically after photo-thrombotic occlusion. We compare the differences between absolute and relative measurements of the functional blood flow responses, and validate FA MESI by comparing baseline measurements to 15-exposure MESI over the sampled flow distributions. We demonstrate the differences measured between the functional outcomes and the regional CBF perfusion over a three week post-occlusion time period. / text

Cerebral blood flow (CBF) measures are central to the investigation of ischemic strokes, spreading depressions, functional and neuronal activation. Laser Speckle Contrast Imaging (LSCI) is an optical imaging technique that has been used to obtain CBF measures in vivo at high spatial and temporal resolutions, by quantifying the localized spatial blurring of backscattered coherent light induced by blood flow. Despite being widely used for biomedical applications, LSCI's critical limitations such as its tendency to underestimate large flow changes and its inability to accurately estimate CBF through a thinned skull have not been overcome. This dissertation presents a new Multi Exposure Speckle Imaging (MESI) technique that combines a new instrument and mathematical model to overcome these limitations. Additionally, in a pilot clinical study, an adapted neurosurgical microscope was used to obtain intra-operative LSCI images of CBF in humans. The MESI instrument accurately estimates experimental constants by imaging backscattered speckles over a wide range of the camera's exposure durations. The MESI mathematical model helps account for light that has scattered from both static and moving particles. In controlled flow experiments using tissue simulating phantoms, the MESI technique was found to estimate large changes in flow accurately and the estimates of flow changes were found to be unaffected by the presence of static particles in these phantoms. In an in vivo experiment in which the middle cerebral artery in mice was occluded to induce ~100% reduction in CBF, not only was the reduction in CBF accurately estimated by the MESI technique but these estimates of CBF changes were found to be unaffected by the presence of a thinned skull. The validity of statistical models used to derive the MESI mathematical model was confirmed using in vivo dynamic light scattering (DLS) measurements of CBF in mice. The MESI technique's potential to estimate absolute values of CBF in vivo was demonstrated by comparing CBF estimates obtained using the MESI technique to DLS measurements. The MESI technique's ability to measure CBF changes quantitatively through a thinned skull makes it particularly useful in chronic and long term studies leading to the development of better, more accurate stroke models. / text

Selon l’organisation mondiale de la santé, dans les pays en développement, la proportion de personnes obèses a presque triplé depuis 1980 et presque doublé dans les pays à revenu élevé. Parmi ces statistiques, en France, 16,8% des hommes et 17,4% des femmes sont obèses. Les taux mondiaux d'obésité devraient monter au cours de la prochaine décennie pour atteindre un cinquième des adultes en 2025. L'obésité est due à de multiples facteurs, dont la consommation excessive d’aliments riches en gras et en sucres, ainsi que des facteurs génétiques, psychosociaux et environnementaux. L'incidence de maladies telles que le cancer, le diabète et les maladies cardiovasculaires est supérieure chez les personnes obèses. L’obésité a également un impact néfaste sur le fonctionnement du cerveau, ce qui entraîne davantage d’accidents vasculaires cérébraux et des maladies neurodégénératives chez les personnes obèses. Une activité cérébrale normale impose des besoins énergétiques dynamiques qui sont satisfaits par le flux sanguin cérébral (Cerebral Blood Flow, CBF). La perfusion adéquate des tissus cérébraux au bon moment et au bon endroit parmi les quelques 160 milliards de cellules qui composent le cerveau adulte humain est vital. Malgré des données obtenues sur des tranches de cerveau concernant les problèmes de barrière hémato-encéphalique chez les personnes obèses, le devenir du CBF au cours de l'obésité n'a pas encore été étudié. Une des raisons à cela est la difficulté à enregistrer le CBF in vivo et de le suivre dans le temps, pendant une activation cérébrale et sur une large échelle avec une résolution spatio-temporelle appropriée. Afin d'évaluer l'influence de l'obésité sur le CBF, au repos et pendant la stimulation sensorielle, nous avons développé une technique optique appelée l'imagerie de contraste laser par exposition multiple (MESI). La technique repose sur le calcul du contraste de speckle, qui est lié à la vitesse des diffuseurs (globules rouges). Il permet une imagerie superficielle à large champ des variations relatives de flux sanguin dans le cortex de la souris. Nous avons caractérisé les performances du système en utilisant des fantômes microfluidiques. L’acquisition du contraste pour différentes durées d’exposition permet de discriminer les diffuseurs statiques et dynamiques (en mouvement) et donc d’obtenir une image quantitative des variations du CBF. Nous avons étudié l'activation cérébrale en utilisant la stimulation olfactive par des flux d'odeurs contrôlés présentés à la souris anesthésiée. Le bulbe olfactif est une structure sensorielle essentielle des mammifères pour le codage des odeurs et il est bien adapté à l'imagerie optique car l’activité neuronale et vasculaire est détectée dans les régions superficielles de cette structure. Nous avons observé une diminution significative du CBF évoqué par stimulation odorante chez les souris obèses (sous régime hyperlipidique) par rapport aux souris témoins (sous régime standard). Chez les souris contrôles, les variations de CBF sont élevées dans les vaisseaux sanguins de grand diamètre et diminuent dans les vaisseaux sanguins de petit calibre. Cette variation dépendant du diamètre est perdue chez les souris obèses qui présentent même un CBF significativement réduit au repos, au cours d'une activité vasculaire spontanée. De plus, afin de mieux comprendre la morphologie du système vasculaire, nous avons commencé l’étude par iDISCO de la densité et la distribution des vaisseaux dans l’ensemble du cerveau in vitro chez des souris obèses comparées aux contrôles. En conclusion, les résultats obtenus sur le CBF chez les souris obèses par la mise au point d’une technique d’imagerie optique à large champ MESI, indiquent que l'obésité impacte le fonctionnement vasculaire en dérégulant le débit sanguin cérébral. / Obesity is a global health threat. Since 1980 the proportion of obese or overweight individuals tripled in developing countries and doubled in high-income countries. In France 16.8% of men and 17.4% of women are obese. In the actual tendency persists, one-fifth of adults worldwide will be obese by 2025. Obesity is characterized by exaggerated weight gain and accumulation of fat tissue and is due to multiple factors including excessive consumption of high fat-sweet food and genetic, psychosocial and environmental factors. It is linked to an increase in the incidence of diseases such as cancer, diabetes and cardiovascular disease. Obesity has also a detrimental impact on brain function leading to higher rate of stroke and neurodegenerative diseases. Normal brain activity imposes dynamic energy requirements. Energy needs are fulfilled by Cerebral Blood Flow (CBF) to perfuse the brain tissue at the right time and the right place among the hundred of billons of cells that compose the human adult brain. Although dysfunction of the blood brain barrier was observed in brain slices, the fate of CBF during obesity in vivo is unknown. One reason for this is the difficulty to record CBF over time in vivo and to follow the time course of activation of large populations of cells with an appropriate spatiotemporal resolution. In order to evaluate the influence of obesity on CBF, at rest and during sensory stimulation, we have developed an optical technique termed multi-exposure speckle contrast imaging (MESI). In the last years, MESI has been validated for imaging relative changes in CBF at the surface of the rodent brain in vivo, the standard mammalian model for brain studies. The technique relies on the calculation of the spatial speckle contrast, which is related to the velocity of scatterers (red blood cells), and allows wide-field imaging of CBF at the mesoscopic level. We have characterized the performances of the system using microfluidic phantoms. We further demonstrated the ability of our MESI system to discriminate the moving and static diffusers contribution and therefore to provide accurate estimate of CBF changes in vivo. The olfactory bulb is a major hub for the processing of olfactory information in the brain of all mammals. It is well suited for optical imaging of brain activation since neuronal and vascular activities are detected very superficial at the surface of this structure. Using MESI, we have studied brain activation in control and obese mice. We have performed olfactory activation by delivering controlled odorants fluxes to anesthetized mice. We observed a significant decrease in odor-evoked CBF with a loss of diameter-dependent regulation of CBF in obese mice (high fat diet) compared to control lean mice (standard diet). We showed that CBF regulation was lost in obese mice even at rest without any stimulation. Furthermore, to gain insights into the morphology of the vascular network, we started the study of the vessels density and distribution in the entire brain using an in vitro iDISCO approach in obese mice compared to control mice. Overall, these findings indicate that obesity can adversely affect CBF at rest and in response to neuronal activation in vivo.