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Elastographie par Résonance Magnétique : Nouvelle méthode d’acquisition fondée sur le contrôle optimal et comparaison de l’ERM avec une technique de rhéologie haute-fréquence

Abstract : Magnetic Resonance Elastography is a non-invasive imaging method enabling in vivo characterization of viscoelastic properties of biological tissues. The first part of this thesis deals with the comparison of viscoelastic properties obtained with MRE and with a high-frequency rheometer having a large excitation frequency range. This large frequency range enables common frequency range to MRE, unlike the comparisons usually performed in the literature. To perform MRE measurements, the excitation device and the MRE sequence were developed and an algorithm reconstructing the viscoelastic properties based on an inversion of Helmholtz equation was implemented and evaluated through simulation. The comparison between MRE/rheology was then performed, first on plastisol phantoms with different viscoelastic properties, and then on bovine liver samples. In both cases, results show a very good agreement between values obtained with MRE and those coming from rheology. The second part of this work presents a new acquisition method for MRE. Conventional MRE sequences use oscillating gradients to encode the wave propagation into the phase image. However, these gradients can restrict MRE applications, as their switching frequencies as well as maximal amplitude are limited. The new acquisition strategy we propose in this thesis encodes the wave propagation directly with RF pulses generated with Optimal Control Theory (OCT), in combination with a constant gradient. An initial experiment of phase control with RF pulses is presented, consisting in creating non-trivial spatial phase patterns in MRI phase images, in the absence of wave propagation. Then, RF pulses adapted to the MRE problem are generated with OCT and phase images obtained with these pulses are compared with conventional MRE acquisitions. Viscoelastic properties reconstructed from these two techniques are similar, validating thus this new acquisition method.
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https://tel.archives-ouvertes.fr/tel-01940918
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Submitted on : Friday, November 30, 2018 - 3:47:06 PM
Last modification on : Wednesday, July 8, 2020 - 12:42:59 PM
Long-term archiving on: : Friday, March 1, 2019 - 2:51:20 PM

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  • HAL Id : tel-01940918, version 1

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Pauline Lefebvre. Elastographie par Résonance Magnétique : Nouvelle méthode d’acquisition fondée sur le contrôle optimal et comparaison de l’ERM avec une technique de rhéologie haute-fréquence. Imagerie médicale. Université de Lyon, 2017. Français. ⟨NNT : 2017LYSEI116⟩. ⟨tel-01940918⟩

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