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Contribution à l'étude de systèmes multispire dérivés des bobines de Helmholtz : application à l'imagerie par résonance magnétique

Abstract : This work of thesis is dedicated to the study of radiofrequency probes with high B1 field homogeneity for Magnetic Resonance Imaging. Compared to Helmholtz pair which presents a 2nd-order homogeneity, the aim is first an improvement of the field homogeneity, while preserving the simplicity of design. The first chapter gives a basic introduction to the NMR and MRI. These aspects are followed by the essential characteristics of the NMR probes design (quality factor, SNR, ). Then, several basic structures of NMR coils are described, particularly the Helmholtz coils. The second and third chapter are dedicated to the design and test of prototype probes, comprising four coaxial rings of wire in a symmetric arrangement on a spherical and on an ellipsoidal surface. Thus, beyond the traditional case of spherical geometry, an original wiring on an ellipsoidal surface is also considered. The aim is to provide a fourth-order or in the optimum case a sixth-order homogeneous field. Moreover, different couplings and original tuning are presented, bringing the structures to four or two tuned (or free) elements. A complete electrical model of the four-coil system taking into account all coupling is presented. Results of comparison tests, in free space and in a NMR spectro-imager, between a Helmholtz pair and our prototype probes are presented, and appear to be in good agreement with theoretical predictions. Globally, this work claims to be a contribution to the study and the comprehension of the four-coil RF systems derived from the Helmholtz pairs.
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http://docnum.univ-lorraine.fr/prive/SCD_T_2007_0014_OULD_AHMED_GHALY.pdf
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https://hal.univ-lorraine.fr/tel-01754262
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Submitted on : Friday, March 30, 2018 - 9:43:06 AM
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  • HAL Id : tel-01754262, version 1

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Sidi Mohamed Ould Ahmed Ghaly. Contribution à l'étude de systèmes multispire dérivés des bobines de Helmholtz : application à l'imagerie par résonance magnétique. Autre. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10014⟩. ⟨tel-01754262⟩

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