Post-Reconstruction Deconvolution of PET Images by Total Generalized Variation Regularization

Improving the quality of positron emission tomography (PET) images, affected by low resolution and high level of noise, is a challenging task in nuclear medicine and radiotherapy. This work proposes a restoration method, achieved after tomographic reconstruction of the images and targeting clinical situations where raw data are often not accessible. Based on inverse problem methods, our contribution introduces the recently developed total generalized variation (TGV) norm to regularize PET image deconvolution. Moreover, we stabilize this procedure with additional image constraints such as positivity and photometry invariance. A criterion for updating and adjusting automatically the regularization parameter in case of Poisson noise is also presented. Experiments are conducted on both synthetic data and real patient images.Comment: First published in the Proceedings of the 23rd European Signal Processing Conference (EUSIPCO-2015) in 2015, published by EURASI

Efficacité, engagement et coopération des étudiants en situation d’apprentissage par problèmes : les principes Agiles peuvent-ils soutenir l’apprentissage ?

L'apprentissage actif est de plus en plus plébiscité à l'heure actuelle dans l'enseignement. Ses principes se traduisent notamment dans l'apprentissage par problèmes (APP), une approche qui favorise la contextualisation des problèmes proposés, l'autonomie et l'auto-régulation de l'étudiant(e). L'APP se base sur le travail en groupe. Cependant, l'accent est mis sur le contenu et les démarches de résolution plutôt que sur la coopération et l'organisation au sein du groupe. Ce mémoire présente la mise en place et l'évaluation d'un dispositif dont l'objectif est de favoriser la coopération entre étudiant(e)s et de les amener à réguler leur fonctionnement de manière autonome. La question de recherche concerne le lien éventuel entre ce dispositif et l'efficacité du groupe voire l'engagement dans le cours. Les premiers résultats montrent une augmentation significative de la perception du dispositif par les étudiant(e)s mais qui ne se traduit pas dans les autres dimensions mesurées (organisation, relations, dynamique de groupe, etc.). Le besoin d'outils d'organisation (partage des tâches, gestion du temps) ressort de l'enquête. Cela justifie la mise en place du dispositif pour l'ensemble des étudiant(e)s même si cela nécessite encore des adaptations et améliorations.Master complémentaire en pédagogie universitaire et de l'enseignement supérieur (horaire décalé), Université catholique de Louvain, 201

Physics-based computational imaging for positron emission tomography and lensless endoscopy

Unraveling the mysteries of life has fascinated humans for millenniums. The emergence of digital computers paved the way to new imaging modalities able to measure properties and signals coming from the inside of the body, without opening it. Computational imaging (CI) was born. CI acquires digital observations that are often not readily understandable (e.g., returning echoes in ultrasound scans). A recovery step is thus necessary to extract useful information. To solve the so-called inverse problem, we resort to an optimization including knowledge about the acquisition process (emission and collection processes, noise corruption, etc.) and the expected properties of the final estimate (e.g., piecewise-smoothness). In this thesis, we focus on two modalities designed to image cellular processes in living organisms: positron emission tomography (PET) and lensless endoscopy (LE). PET imaging is widely used to get information about patient physiological activity. It suffers from blurring and high level of noise. LE exploits fluorescence phenomenon to capture biological information at a micrometer scale. A challenging task is to avoid tissue photobleaching. The dissertation addresses two inverse problems related to PET and LE. First, we study the deblurring of reconstructed PET images polluted by a high level of noise in non-blind and blind contexts. Then, we explore acquisition and reconstruction strategies for LE that exploits nice properties of the sensing operator to collect far less observations as in a traditional scheme. This approach leads to both reduced acquisition time and light exposure.(FSA - Sciences de l'ingénieur) -- UCL, 202

La tombe SP4041 de la place Eugène Wernert à Lyon (Rhône) et son mobilier " anachronique "

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Des apparences parfois trompeuses : la tombe SP4041 de la place E. Wernert à Lyon (Rhône)

International audienceLa fouille de la place E. Wernert à Lyon a permis la poursuite de la mise au jour d’une vaste nécropole, en partie fouillée en 1980 par J.-F. Reynaud (Reynaud 1980), dont l’occupation est comprise entre le IVe s. et le VIe s. Elle comprend 817 individus, dont 799 en position primaire. Les sépultures, en contenants périssables (coffrages en bois, monoxyles, cercueils cloués…), ou installées dans des sarcophages, comportent peu de mobilier et seules seize d’entre-elles sont associées à des dépôts. La sépulture SP4041 est celle d’une femme âgée de plus de 40 ans, installée dans un cercueil cloué, lui-même disposé dans un sarcophage en calcaire. Cette tombe a livré plusieurs objets déposés ou portés, dont la datation n’est pas homogène. Le mobilier de la sépulture SP4041 se compose de fragments de plaques en fer non déterminables, d’une fibule, d’une clef-bague à translation en alliage cuivreux, d’une monnaie et d’un balsamaire en verre. L’attribution chronologique des artefacts de la sépulture SP4041 n’est pas homogène et s’intègre dans une large fourchette allant du Ier s. av. J.-C. au Ve s. ap. J.-C., fourchette revue à la lumière d’une datation radiocarbone. Par ailleurs, l’architecture de la sépulture est assez complexe et pose question, notamment sur l’écart possible entre la fabrication du sarcophage et son utilisation pour disposer le sujet dans son cercueil cloué.Cet exemple particulier, tant sur le plan de la typologie que sur celui du mobilier associé, démontre l’importance du travail pluridisciplinaire afin de confronter les résultats entre chaque discipline et d’établir des protocoles d’études communs

Image Deconvolution by Local Order Preservation of Pixels Values

Positron emission tomography is more and more used in radiation oncology, since it conveys useful functional information about cancerous lesions. Its rather low spatial resolution, however, prevents accurate tumor delineation and heterogeneity assessment. Post-reconstruction deconvolution with the measured point-spread function can address this issue, provided it does not introduce undesired artifacts. These usually result from inappropriate regularization, which is either absent or making too strong assumptions about the structure of the signal. This paper proposes a deconvolution method that is based on inverse problem theory and involves a new regularization term that preserves local pixel value order relationships. Such regularization entails relatively mild constraints that are directly inferred from the observed data. This paper investigates the theoretical properties of the proposed regularization and describes its numerical implementation with a primal-dual algorithm. Preliminary experiments with synthetic images are presented to compare quantitatively and qualitatively the proposed method to other regularization schemes, like TV and TGV.Positron emission tomography is more and more used in radiation oncology, since it conveys useful functional information about cancerous lesions. Its rather low spatial resolution, however, prevents accurate tumor delineation and heterogeneity assessment. Post-reconstruction deconvolution with the measured point-spread function can address this issue, provided it does not introduce undesired artifacts. These usually result from inappropriate regularization, which is either absent or making too strong assumptions about the structure of the signal. This paper proposes a deconvolution method that is based on inverse problem theory and involves a new regularization term that preserves local pixel value order relationships. Such regularization entails relatively mild constraints that are directly inferred from the observed data. This paper investigates the theoretical properties of the proposed regularization and describes its numerical implementation with a primal-dual algorithm. Preliminary experiments with synthetic images are presented to compare quantitatively and qualitatively the proposed method to other regularization schemes, like TV and TGV

Compressive Imaging Through Optical Fiber with Partial Speckle Scanning

Fluorescence imaging through ultrathin fibers is a promising approach to obtain high-resolution imaging with molecular specificity at depths much larger than the scattering mean-free paths of biological tissues. Such imaging techniques, generally termed lensless endoscopy, rely upon the wavefront control at the distal end of a fiber to coherently combine multiple spatial modes of a multicore (MCF) or multimode fiber (MMF). Typically, a spatial light modulator (SLM) is employed to combine hundreds of modes by phase-matching to generate a high-intensity focal spot. This spot is subsequently scanned across the sample to obtain an image. We propose here a novel scanning scheme, partial speckle scanning (PSS), inspired by compressive sensing theory, that avoids the use of an SLM to perform fluorescent imaging with optical fibers with reduced acquisition time. Such a strategy avoids photo-bleaching while keeping high reconstruction quality. We develop our approach on two key properties of the MCF: (i) the ability to easily generate speckles, and (ii) the memory effect that allows one to use fast scan mirrors to shift light patterns. First, we show that speckles are subexponential random fields. Despite their granular structure, an appropriate choice of the reconstruction parameters makes them good candidates to build efficient sensing matrices. Then, we numerically validate our approach and apply it on experimental data. The proposed sensing technique outperforms conventional raster scanning: higher reconstruction quality is achieved with far fewer observations. For a fixed reconstruction quality, our speckle scanning approach is faster than compressive sensing schemes which require changing the speckle pattern for each observation

Les mutations des recettes de l’industrie verrière en France au Moyen Age: mise en évidence de solutions multiples adaptées aux contextes locaux

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Evolution of glass recipes during the Early Middle Ages in France : analytical evidence of multiple solutions adapted to local contexts

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