0000000001167239
AUTHOR
Denis Grenier
showing 9 related works from this author
Contrôle Optimal appliqué au contrôle de la phase en IRM : simulations et expériences sur fantômes
2017
National audience; IntroductionLes techniques IRM utilisant la phase du signal IRM, à la place ou en complément de l’amplitude, sont de plus en plus nombreuses. Dans ces techniques, la phase est gérée par l’application de gradients. Nous proposons ici de contrôler la phase du signal directement avec des impulsions RF. Pour cela, nous avons utilisé la théorie du contrôle optimal1 et calculé des impulsions RF optimisées pour atteindre des états cibles (dans notre cas, des motifs de phase) préalablement définis. Dans cette étude, une preuve de faisabilité de contrôle de la phase IRM par impulsions RF est présentée au travers de simulations (avec le logiciel ODIN2) ainsi que d’expériences IRM s…
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…
Magnetic resonance elastography without oscillating gradients
2017
International audience
Contrôle optimal appliqué à l’Elastographie par Résonance Magnétique avec un gradient constant: expériences ex vivo et in vitro
2019
International audience
Optimal control design of preparation pulses for contrast optimization in MRI
2017
Abstract This work investigates the use of MRI radio-frequency (RF) pulses designed within the framework of optimal control theory for image contrast optimization. The magnetization evolution is modeled with Bloch equations, which defines a dynamic system that can be controlled via the application of the Pontryagin Maximum Principle (PMP). This framework allows the computation of optimal RF pulses that bring the magnetization to a given state to obtain the desired contrast after acquisition. Creating contrast through the optimal manipulation of Bloch equations is a new way of handling contrast in MRI, which can explore the theoretical limits of the system. Simulation experiments carried out…
A simplified framework to optimize MRI contrast preparation
2018
PURPOSE This article proposes a rigorous optimal control framework for the design of preparation schemes that optimize MRI contrast based on relaxation time differences. METHODS Compared to previous optimal contrast preparation schemes, a drastic reduction of the optimization parameter number is performed. The preparation scheme is defined as a combination of several block pulses whose flip angles, phase terms and inter-pulse delays are optimized to control the magnetization evolution. RESULTS The proposed approach reduces the computation time of B 0 -robust preparation schemes to around a minute (whereas several hours were required with previous schemes), with negligible performance loss. …
MRI phase control with Optimal Control Theory
2017
International audience
A Simplified Framework for Contrast Optimization in MRI
2018
International audience
Contrast Preparation Pulses Robust to B1 and B0 inhomogeneities: an Optimal Control Approach
2018
International audience