Search results for "Bioengineering"
showing 10 items of 1963 documents
MRI phase control with Optimal Control Theory
2017
International audience
Constant gradient magnetic resonance elastography experiments on phantom and bovine liver
2019
International audience; SynopsisMagnetic Resonance Elastography (MRE) is performed by the application of motion-sensitive gradients. In this study, RF pulses are designed with an optimal control algorithm to obtain a desired magnetization phase distribution. Such pulse, in presence of a constant gradient, allows tosimultaneously perform spatially selective excitation and motion encoding. This offers some advantages when compared to standard MRE encoding strategy. Simulations, phantom and ex vivo experiments show that phase-to-noise ratios are improved. These results demonstrate that optimal control-based pulses can be used to encode motion in the MRE excitation phase with relevant advantage…
Optimizing MRI contrast with optimal control theory
2016
International audience; Magnetic Resonance Imaging (MRI) uses the difference in tissue relaxation times to create contrast. Various image weightings can be obtained by tuning acquisition parameters which are usually empirically defined. In this article, optimal control theory is used to design excitation pulses that produce the optimal contrast between given tissues. The designed pulses are tested on numerical phantoms with and without magnetic field inhomogeneities and for the first time in vitro on a small-animal MRI. The reasonable match between simulation and real experiments is promising for the development of such pulses in further in vivo applications.
Design d'impulsions RF par contrôle optimal pour l'optimisation du contraste en IRM : applications in vivo
2017
National audience; But : Le design d’impulsions radio-fréquence (RF) par contrôle optimal pour l’optimisation du contraste a récemment été proposé [1]. Ces impulsions garantissent un certain degré d’optimalité sur le contraste obtenu, qui s’approche de la borne théorique. Jusqu’alors, leur utilisation a été validée sur IRM lors d’expériences in vitro uniquement [2]. Cette étude étend ces résultats in vivo sur cerveaux de rat et souris.Méthode : Le problème de contrôle optimal, via la résolution du Principe du Maximum de Pontryagin [3] (PMP), consiste à calculer le contrôle qui optimise une fonction de coût, connaissant la dynamique du système à optimiser. Appliqué à l’IRM, il s’agit de calc…
Optimal Control Pulse Design for Contrast in MRI: in vivo applications
2017
International audience; Optimal control RF pulse design has recently been proposed to address the optimization of image contrast in MRI - in order to explore the theoretical contrast bound of a given imaged system. Their use has recently been validated on a real MRI scanner to contrast various in vitro samples. This abstract extends these results to in vivo applications, and shows that contrasts obtained with standard weighting strategies on rat and mouse brains can be improved or inverted. This demonstrates both the interest and flexibility that one can get when using optimal contrast pulses for in vitro and in vivo applications.
Influence du degré de contrôle rétroactif sur l'apprentissage de séquences répétées dans une tâche de poursuite de cible
2011
International audience; à venir
Effet des émotions sur le mouvement volontaire chez l'enfant témoin et autiste, un exemple: la locomotion dirigée vers un but
2009
International audience; à venir
Impulsions d'excitation basse énergie robustes aux inhomogénéités B1
2019
International audience
A Simplified Framework for Contrast Optimization in MRI
2018
International audience
Contrôle optimal appliqué à l’Elastographie par Résonance Magnétique avec un gradient constant: expériences ex vivo et in vitro
2019
International audience