Analyse automatique des images échographiques de la colonne vertébrale

Résumé L'échographie est une modalité d'imagerie médicale généralement utilisée pour visualiser les tissus mous dans différentes applications cliniques. Cette technique est très avantageuse étant donné son faible coût, sa portabilité et surtout l'absence de rayons ionisants pour former des images. Cependant, le contenu de ces images est complexe et peut être difficile à interpréter même pour un expert. De plus, afin d'obtenir des images échographiques exploitables, un positionnement adéquat de la sonde est nécessaire lors de l'acquisition. Ces deux inconvénients sont encore plus importants lors de l'acquisition d’images de structures osseuses. Ces structures réfléchissent entièrement les ondes ultrasonores, créant ainsi des surfaces très brillantes et des ombres acoustiques en dessous d'elles, rendant ainsi leur interprétation encore plus complexe. Dans le cas d’une vertèbre, la surface de l'apophyse épineuse est tellement petite que sa brillance est particulièrement dépendante de l'orientation et de la position de la sonde. D'autre part, la forme complexe de la vertèbre rend la frontière de son ombre acoustique plus difficile à définir. Cependant l'utilisation de l'échographie de la colonne vertébrale à la place de radiographies lors du suivi clinique de patients atteints de scoliose pourrait réduire le cumul de radiation. Plusieurs méthodes utilisant l'échographie ont été développées ces dernières années afin d’évaluer la scoliose ou de réajuster le corset pour des patients atteints de scoliose idiopathique adolescente (SIA). Ces méthodes requièrent des images de bonne qualité et une segmentation manuelle du contenu. Dans ce projet, nous proposons d’effectuer une analyse automatique des images échographiques vertébrales afin de comprendre le modèle de formation de ces images et de segmenter automatiquement les structures d’intérêt. Dans un premier temps, nous avons développé une méthode de segmentation automatique de l'apophyse épineuse et de l'ombre acoustique dans les images échographiques vertébrales afin d'aider l'utilisateur à interpréter ce type d'images. Cette méthode s'appuie, tout d'abord, sur l’extraction de différentes caractéristiques et leur validation afin de sélectionner l’ensemble le plus pertinent. Puis un classifieur est utilisé afin d'associer chaque pixel de l'image à une des trois régions suivantes : apophyse épineuse, ombre acoustique ou autres tissus. Finalement, une étape de régularisation est appliquée afin de prendre en compte les différentes propriétés des vertèbres. Nous avions une base de données contenant 181 images échographiques, mais nous n'en avons utilisé que 107, car seules celles-ci avaient une qualité acceptable. Un taux de classification de 84% pour l’apophyse épineuse et de 92% pour l’ombre acoustique ont été obtenus. De plus, le centroïde de l’apophyse épineuse segmentée se trouvait en moyenne à 0.38 mm de celui de la vérité terrain, provenant d’une segmentation manuelle validée par un radiologue. Nous avons aussi évalué la précision de la méthode proposée en comparant les régions segmentées automatiquement à celles délimitées manuellement et avons obtenu un coefficient de similarité DICE de 0.88 pour l’ombre acoustique et de 0.72 pour l’apophyse épineuse.----------Abstract Ultrasound (US) imaging is a medical imaging modality that is often used to visualize soft tissues in the human body in various clinical applications. This technique has several important advantages, in particular its low cost, portability, and the fact that it is radiation-free. However, the content of US images is rather complex and can be hard to interpret even for an expert. Furthermore, the quality of the content of US images will depend of the positioning of the probe during the acquisition. When measuring bone surfaces, these two disadvantages are accentuated. Indeed, the acoustic waves are entirely reflected by these hard structures, thereby creating bright surfaces with acoustic shadows below them, which make the interpretation of such images even more challenging. In the case of a vertebra, the surface of the spinous process is so small that its appearance in US images will strongly depend on the orientation and position of the probe. Moreover, it can be difficult to determine the boundary of the acoustic shadow created by the bone structure given the complicated shape of the vertebra. Nevertheless, in the clinical monitoring of scoliosis, using US images of the spine instead of X-rays could be very useful to reduce the cumulative radiation received by patients. In recent years, several methods using US imaging to evaluate scoliosis, or to adjust the brace in the treatment of adolescent idiopathic scoliosis (AIS), have been developed. These methods require good quality images and use manual segmentation of the image content. In this project, we propose a framework for the automatic analysis of US images of the spine (vertebrae) that utilizes an image formation model and an automatic segmentation of the regions of interest. First, we developed an automatic segmentation method to detect the spinous process and the acoustic shadow in the US images, aimed at helping the end user interpret the images. This method uses feature extraction and selection process in order to determine the most relevant set of features. The aim of the classification task is to discriminate three different regions: spinous process, acoustic shadow and other tissues. An LDA classifier is used to assign each image pixel to one of the three regions. Finally, we apply a regularization step which exploits several properties of vertebrae. Using a database of 107 US images, we obtained a classification rate of 84% for the spinous process and 92% for the acoustic shadow. In addition, the centroid of the automatically segmented spinous process was located 0.38 mm on average from that of the ground truth, as provided by a manual labelling that was validated by a radiologist. We also compared the automatically and manually segmented regions and obtained DICE similarity coefficients of 0.72 and 0.88 for the spinous process and acoustic shadow respectively

Gaze Behaviour During Collision Avoidance Between Walkers: A Preliminary Study to Design an Experimental Platform

International audienceWhen walking, vision is the main source of information that allows us to navigate safely by detecting potential collisions with other walkers. In order to gain a better understanding of the relationship between gaze activity and kinematics of motion during pedestrian interactions, we present in this paper a preliminary study towards designing a more comprehensive experimental platform. In this study, participants are asked to avoid collisions with an upcoming virtual character using a joystick, while we measure their gaze behaviours using an eye-tracker. As we are interested in the effects of potential collisions on gaze activity, i.e., where and when participants look to avoid potential future collisions, we display in our experiment a virtual character for which we vary the initial Time To Closest Approach (ttca) and Distance of Closest Approach (dca) values, to change its risk of collision with our participant. We then measure participant trajectory adjustments and gaze activity during the interaction. Our preliminary results show which type of data this platform produces, and demonstrate the interest of designing more comprehensive experiences and tools to analyze both gaze activity and kinematics

Crowd Navigation in VR: exploring haptic rendering of collisions

International audienceVirtual reality (VR) is a valuable experimental tool for studying human movement, including the analysis of interactions during locomotion tasks for developing crowd simulation algorithms. However, these studies are generally limited to distant interactions in crowds, due to the difficulty of rendering realistic sensations of collisions in VR. In this work, we explore the use of wearable haptics to render contacts during virtual crowd navigation. We focus on the behavioural changes occurring with or without haptic rendering during a navigation task in a dense crowd, as well as on potential after-effects introduced by the use haptic rendering. Our objective is to provide recommendations for designing VR setup to study crowd navigation behaviour. To this end, we designed an experiment (N=23) where participants navigated in a crowded virtual train station without, then with, and then again without haptic feedback of their collisions with virtual characters. Results show that providing haptic feedback improved the overall realism of the interaction, as participants more actively avoided collisions. We also noticed a significant after-effect in the users' behaviour when haptic rendering was once again disabled in the third part of the experiment. Nonetheless, haptic feedback did not have any significant impact on the users' sense of presence and embodiment

Foules virtuelles immersives : évaluation du comportement des piétons en réalité virtuelle

Virtual Reality (VR) has become more and more used as a tool to study human behaviour. Indeed, its use provides absolute control over experimental conditions and can reproduce the same stimulus for all participants. In this thesis, we use VR to investigate pedestrian behaviour in crowds in order to subsequently improve crowd simulators. In particular we are interested in a coupled analysis of locomotion and gaze in order to understand and model the interaction neighbourhood during navigation. In our first work, we evaluated the impact of VR on gaze activity during an interaction between two pedestrians, in a study where participants performed a collision avoidance task in a real and virtual environment. We then studied a more complex situation which is the navigation in a crowded street. We again evaluated the impact of VR on gaze activity and then explored the impact of crowd density on this activity. Finally, in a third study we simulated the collisions that occur when navigating in a dense crowd using haptic rendering, and evaluated the influence of such rendering on participants' locomotion. In conclusion, our results show that VR is a relevant tool to study pedestrian behaviour in crowds. In particular, with recent technological innovations, this tool is appropriate for the study of gaze activity, which to date has been little explored for this kind of situation.La réalité virtuelle (RV) est devenu un outil de plus en plus utilisé afin d'étudier le comportement humain. En effet, son utilisation permet d'avoir un contrôle absolu sur les conditions expérimentales et de reproduire le même stimulus pour tous les participants. Dans cette thèse, nous utilisons la RV pour étudier le comportement piétons dans les foules afin par la suite d'améliorer les simulateurs de foules. En particulier nous nous intéressons à l'analyse couplée de la marche et du regard pour pouvoir comprendre et modéliser le voisinage d'interaction lors de la navigation. Dans nos premiers travaux, nous nous avons évalué l'impact de la RV sur l'activité du regard lors d’une interaction entre deux piétons, dans une étude où les participants réalisaient une tâche d'évitement de collision dans un environnement réel et virtuel. Par la suite nous nous sommes intéressés à une situation plus complexe qui est la navigation dans une rue peuplée. Nous avons de nouveau évalué l'impact de la RV sur l'activité du regard, puis nous nous sommes intéressé à l'impact de la densité de la foule sur cette activité. Finalement, dans une troisième étude nous avons simulé, en utilisant un rendu haptique, les collisions se produisant lors de la navigation dans une foule dense, et nous avons évalué l'influence de tel rendu sur la navigation des participants. En conclusion, nos résultats montrent que la réalité virtuelle est un outil pertinent pour l'étude du comportement des piétons dans les foules. En particulier, avec les récentes innovations technologiques, cet outil est adapté à l'étude de l'activité du regard, qui a d’ailleurs été peu explorée jusqu'à présent pour ce type de situation

Study of the fatigue behavior of thermoplastic blends (PP / EVA)

International audiencePolymer blends are a widely used technic to upgrade the properties of the constituents. Polypropylene (PP) is used in many industrial applications; it became classical to mix the PP with another material. In this study, we focus on the polypropylene mixed with ethylene vinyl acetate (EVA). The main goal of this work is to characterize several blends with varying composition. Firstly, we studied their thermo-mechanical properties with DMA, DSC and tensile test at different strain rates and compared their results with each pure materials (PP and EVA) in order to understand the miscibility of the blend. In the second step, the fatigue behavior was studied by using infrared thermography to relate fatigue damages to heat source. Indeed, the idea is to confront the method developed to get quick information on fatigue behaviors and phenomena such as fracture, crack and necking. Moreover, the influence of the fatigue frequency was also investigated since the viscous behavior of each constituent is different. This series of tests is also the premise of a comparative study in order to understand the different blends mechanical behaviors. First, by using test like X-ray diffraction (WAXS) with a step-by-step test on fatigue, it is possible to follow the several crystalline populations regarding the level of stress. In correlation with X-ray micro-computed tomography (μCT), we follow the different types of damaging inside the bulk material. In the second time, by doing a cycling method in instrumented indentation we will compare the different results in fatigue with their equivalent in cyclic instrumented indentation

The effect of temperature on fatigue behavior of chloroprene rubber

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Détermination de la température à coeur dans des élastomères sollicités dynamiquement

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Study of the Fatigue Behavior of the Polychloroprene Rubber with Stress Variation Tests

3rd International Conference on Material and Component Performance under Variable Amplitude Loading, \VAL\ 2015International audienceAbstract In this study we study the fatigue behavior of a polychloroprene rubber using designed specific variable amplitude tests to gather insight into such material behavior. Firstly, increasing force amplitude block load tests were carried out that permits us to determine the stress amplitude at which fatigue damage is significant. In a second series of tests block programmed tests were carried out. During these tests the hysteresis energy and stiffness were also measured. These measurements bring out possibly a competition between two mechanisms the crystallization effect and the effect of crack propagation. The first mechanism tends to increase the stiffness while the second decreases the stiffness

Study of the fatigue behavior of the chloroprene rubber for uniaxial tests with infrared method

International audienceRubber-like materials are widely used in the industry, aeronautic or automotive. In these applications,fatigue damage must be taken into account, which requires very long and costly experimental campaigns.One of the main goals of the research on this kind of materials is to improve the prediction of fatiguelife with shorter and cheaper tests. This paper describes the first part of an ongoing research aboutthe study of the fatigue behavior of dumbbell specimen made of polychloroprene with infrared thermography.It deals with the definition of two new thermal parameters for the fatigue behavior analysis. Thefirst one is the heating rate and is defined in the first 1500 cycles giving a linear relationship with the stabilizedtemperature of the specimen. The second thermal parameter is the number of cycles until the stabilizationof the surface temperature of the sample. Changes in the thermal behavior observed durin