Développement de la tomographie intra-vitale au K-edge avec la caméra à pixels hybrides XPAD3

The hybrid pixel camera XPAD3 integrated in the micro-CT PIXSCAN IIis a new devicedeveloped by the imXgam team at CPPM for which photon counting replaces charge integrationused in standard X-ray CT. This novel approach involves advantages, in particularthe absence of dark noise and the ability to set an energy threshold on each pixel of thedetected photons. This features has been exploited during this thesis work for standardsmall animal preclinical imaging and permitted to establish the faisability of ex vivo, andthen in vivo labelling of marcrophages.On another hand, the ability of this camera is of uppermost importance for the developmentof K-edge imaging approaches, which exploit spectral information on the countedphotons. K-edge imaging permits to identify contrast agent compartiments with regardsto bones in classical radiography. K-edge imaging is obtained by selecting, for each pixelcalibration, those pixel that are set at one of the three different thresholds around theK-shell’s binding energy of the selected contrast agents and then, to proceed with a subtractionanalysis to the images obtained above and below the K-edge energy.We develop a new way of calibrating the XPAD3 detector that permits to provide theproof of concept of a patent owned by the imXgam team, and to obtain the first results onliving mice by dividing the acquisition time by three with a compromise on the resolution.This novel approach can be implemented in "two colours" in order to separate clearly twodifferent contrast agents. This brings a new way to visualize biological information and toprovide possible future approaches for the study of the inter-dependance of vascularisationand inflammation during the tumor development.La caméra à pixels hybrides XPAD3 intégrée dans le micro-tomodensitomètre PIXSCANII est un nouveau dispositif développé par l’équipe imXgam au CPPM dans lequelle comptage de photons remplace l’intégration de charges utilisée dans les systèmes deradiographie standard. La caméra XPAD3 apporte des avantages, en particulier l’absencede bruit de courant noir et la possibilité d’imposer un seuil de discrimination sur chaquepixel. Ces particularités ont pu être exploitées au cours de ce travail de thèse en imageriepréclinique classique sur petit animal et ont permis de faire la preuve de faisabilité d’unmarquage ex-vivo puis intra-vital des macrophages.D’autre part les capacités de cette caméra sont intéressantes pour le développement d’unenouvelle méthode d’imagerie spectrale dite au K-edge. L’imagerie au K-edge permet dedifférencier des compartiments contenant un agent de contraste par rapport à l’os dans desradiographies classiques. Elle est obtenue via l’étalonnage de trois différents seuils autourde l’énergie de liaison de la couche K de l’agent de contraste considéré. Le développementd’un nouvel d’étalonnage avec l’utilisation de pixels composites a permis d’établir la preuvede concept d’un brevet déposé par l’équipe imXgam et d’obtenir les premiers résultatssur souris vivantes en divisant le temps d’acquisition par trois avec un compromis sur larésolution spatiale.Cette nouvelle approche peut être implémentée en « deux couleurs » pour séparer deuxdifférents types d’agents de contraste. Ceci offre une nouvelle manière de visualiser desinformations biologiques pertinentes dans un contexte applicatif visant à étudier de manièredynamique (longitudinale) l’interdépendance de la vascularisation et de la réponseimmunitaire au cours du développement tumoral

Consistency of timbre patterns in expressive music performance

International audienceMusical interpretation is an intricate process due to the inter- action of the musician's gesture and the physical possibilities of the instrument. From a perceptual point of view, these elements induce variations in rhythm, acoustical energy and timbre. This study aims at showing the importance of timbre variations as an important attribute of musical interpretation. For this purpose, a general protocol aiming at emphasizing specific timbre patterns from the analysis of recorded musical sequences is proposed. An example of the results obtained by analyzing clarinet sequences is presented, showing stable timbre variations and their correlations with both rhythm and energy deviations. this study, we aim at checking if timbre also follows systematic variations on natural clarinet sounds. We shall first describe a general methodology developed to analyze and compare recorded musical performances in order to point out consistency of timbre, rhythmic and intensity patterns in expressive music performance. An application of this methodol- ogy to twenty recorded musical sequences of the same clarinettist is then given. Eventually, we show that timbre, as rhythm and in

Time-Frequency multipliers for sound synthesis

International audienceTime-frequency analysis and wavelet analysis are generally used for providing signal expansions that are suitable for various further tasks such as signal analysis, de-noising, compression, source separation, ... However, time-frequency analysis and wavelet analysis also provide efficient ways for constructing signals' transformations. They are modelled as linear operators that can be designed directly in the transformed domain, i.e. the time-frequency plane, or the time-scale half plane. Among these linear operators, transformations that are diagonal in the time-frequency or time scale spaces, i.e. that may be expressed by multiplications in these domains, deserve particular attention, as they are extremely simple to implement, even though their properties are not necessarily easy to control. This work is a first attempt for exploring such approaches in the context of the analysis and the design of sound signals. We study more specifically the transformations that may be interpreted as linear time-varying (LTV) systems (often called time-varying filters). It is known that under certain assumptions, the latter may be conveniently represented by pointwise multiplication with a certain time frequency transfer function in the time-frequency domain. The purpose of this work is to examine such representations in practical situations, and investigate generalizations. The originality of this approach for sound synthesis lies in the design of practical operators that can be optimized to morph a given sound into another one, at a very high sound quality

Adjusting the Spectral Envelope Evolution of Transposed Sounds with Gabor Mask Prototypes

International audienceAudio samplers often require to modify the pitch of recorded sounds in order to generate scales or chords. This article tackles the use of Gabor masks and their capacity to improve the perceptual realism of transposed notes obtained through the classical phase-vocoder algorithm. Gabor masks can be seen as operators that allows the modification of time-dependent spectral content of sounds by modifying their time-frequency representation. The goal here is to restore a distribution of energy that is more in line with the physics of the structure that generated the original sound. The Gabor mask is elaborated using an estimation of the spectral envelope evolution in the time-frequency plane, and then applied to the modified Gabor transform. This operation turns the modified Gabor transform into another one which respects the estimated spectral envelope evolution, and therefore leads to a note that is more perceptually convincing

Sound and Posture: an Overview of Recent Findings

International audienceEven if it has been neglected for a long time, the sound and posture domain seemed to arouse an increasing interest in recent years. In the present position paper, we propose to present an overview of our recent findings on this field and to put them in perspective with the literature. We will bring evidence to support the view that spatial cues provided by auditory information can be integrated by human for a better postural control

The influence of horizontally rotating sound on standing balance

International audiencePostural control is known to be the result of the integration and processing of various sensory inputs by the central nervous system. Among the various afferent inputs, the role of auditory information in postural regulation has been addressed in relatively few studies, which led to conflicting results. The purpose of the present study was to investigate the influence of a rotating auditory stimulus, delivered by an immersive 3D sound spatialization system, on the standing posture of young subjects. The postural sway of 20 upright, blindfolded subjects was recorded using a force platform. Use of various sound source rotation velocities followed by sudden immobilization of the sound was compared with two control conditions: no sound and a stationary sound source. The experiment showed that subjects reduced their body sway amplitude and velocity in the presence of rotating sound compared with the control conditions. The faster the sound source was rotating, the greater the reduction in subject body sway.Moreover, disruption of subject postural regulation was observed as soon as the sound source was immobilized. These results suggest that auditory information cannot be neglected in postural control, and that it acts as additional information influencing postural regulation