3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD

CHOUCINO, MARCOS

doi:10.23889/SUthesis.58414

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3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD / MARCOS CHOUCINO

Swansea University Author: MARCOS CHOUCINO

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DOI (Published version): 10.23889/SUthesis.58414

Abstract

Magnetic Resonance Imaging (MRI) scanners have become an essential tool in the medi-cal industry due to their ability to produce high resolution images of the human body. To generate an image of the body, MRI scanners combine strong static magnetic fields with transient gradient magnetic fields. The...

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Published:	Swansea 2021
Institution:	Swansea University
Degree level:	Doctoral
Degree name:	Ph.D
Supervisor:	Ledger, Paul D. ; Gil, Antonio J. ; Mallett, M. ; Zlotnik, S.
URI:	https://cronfa.swan.ac.uk/Record/cronfa58414
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first_indexed	2021-10-19T14:33:08Z
last_indexed	2021-10-20T03:24:00Z
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The interaction of these magnetic fields with the con-ducting components present in superconducting MRI scanners gives rise to an important problem in the design of new MRI scanners. The transient magnetic fields give rise to the appearance of eddy currents in conducting components. These eddy currents, in turn, result in electromagnetic stresses, which cause the conducting components to deform and vibrate. The vibrations are undesirable as they lead to a deterioration in image quality (with image artefacts) and to the generation of noise, which can cause patient discomfort. The eddy currents, in addition, lead to heat being dissipated and deposited into the cryo-stat, which is filled with helium in order to maintain the coils in a superconducting state. This deposition of heat can cause helium boil off and potentially result in a costly magnet quench. Understanding the mechanisms involved in the generation of these vibrations and the heat being deposited into the cryostat are, therefore, key for a successful MRI scanner design. This involves the solution of a coupled magneto-mechanical problem, which is the focus of this work.In this thesis, a new computational methodology for the solution of three-dimensional (3D) magneto-mechanical coupled problems with application to MRI scanner design is presented. To achieve this, first an accurate mathematical description of the magneto-mechanical coupling is presented, which is based on a Lagrangian formulation and the assumption of small displacements. Then, the problem is linearised using an AC-DC splitting of the fields, and a variational formulation for the solution of the linearised prob-lem in a time-harmonic setting is presented. The problem is then discretised using high order finite elements, where a combination of hierarchical H1 and H(curl) basis func-tions is used. An efficient staggered algorithm for the solution of the coupled system is proposed, which combines the DC and AC stages and makes use of preconditioned iter-ative solvers when appropriate. This finite element methodology is then applied to a set of challenging academic and industrially relevant problems in order to demonstrate its accuracy and efficiency.This finite element methodology results in the accurate and efficient solution of the magneto-mechanical problem of interest. However, in the design stage of a new MRI scanner, this coupled problem must be solved repeatedly for varying model parameters such as frequency or material properties. Thus, even if an efficient finite element solver is available for the solution of the coupled problem, the need for these repeated simulations result in a bottleneck in terms of computational cost, which leads to an increase in design time and its associated financial implications. Therefore, in order to optimise this process, the application of Reduced Order Modelling (ROM) techniques is considered. A ROM based on the Proper Orthogonal Decomposition (POD) method is presented and applied to a series of challenging MRI configurations. 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spelling	2021-10-19T16:30:08.0951998 v2 58414 2021-10-19 3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD 51039d0f5cc6da720b741bf5fbcb04c9 MARCOS CHOUCINO MARCOS CHOUCINO true false 2021-10-19 Magnetic Resonance Imaging (MRI) scanners have become an essential tool in the medi-cal industry due to their ability to produce high resolution images of the human body. To generate an image of the body, MRI scanners combine strong static magnetic fields with transient gradient magnetic fields. The interaction of these magnetic fields with the con-ducting components present in superconducting MRI scanners gives rise to an important problem in the design of new MRI scanners. The transient magnetic fields give rise to the appearance of eddy currents in conducting components. These eddy currents, in turn, result in electromagnetic stresses, which cause the conducting components to deform and vibrate. The vibrations are undesirable as they lead to a deterioration in image quality (with image artefacts) and to the generation of noise, which can cause patient discomfort. The eddy currents, in addition, lead to heat being dissipated and deposited into the cryo-stat, which is filled with helium in order to maintain the coils in a superconducting state. This deposition of heat can cause helium boil off and potentially result in a costly magnet quench. Understanding the mechanisms involved in the generation of these vibrations and the heat being deposited into the cryostat are, therefore, key for a successful MRI scanner design. This involves the solution of a coupled magneto-mechanical problem, which is the focus of this work.In this thesis, a new computational methodology for the solution of three-dimensional (3D) magneto-mechanical coupled problems with application to MRI scanner design is presented. To achieve this, first an accurate mathematical description of the magneto-mechanical coupling is presented, which is based on a Lagrangian formulation and the assumption of small displacements. Then, the problem is linearised using an AC-DC splitting of the fields, and a variational formulation for the solution of the linearised prob-lem in a time-harmonic setting is presented. The problem is then discretised using high order finite elements, where a combination of hierarchical H1 and H(curl) basis func-tions is used. An efficient staggered algorithm for the solution of the coupled system is proposed, which combines the DC and AC stages and makes use of preconditioned iter-ative solvers when appropriate. This finite element methodology is then applied to a set of challenging academic and industrially relevant problems in order to demonstrate its accuracy and efficiency.This finite element methodology results in the accurate and efficient solution of the magneto-mechanical problem of interest. However, in the design stage of a new MRI scanner, this coupled problem must be solved repeatedly for varying model parameters such as frequency or material properties. Thus, even if an efficient finite element solver is available for the solution of the coupled problem, the need for these repeated simulations result in a bottleneck in terms of computational cost, which leads to an increase in design time and its associated financial implications. Therefore, in order to optimise this process, the application of Reduced Order Modelling (ROM) techniques is considered. A ROM based on the Proper Orthogonal Decomposition (POD) method is presented and applied to a series of challenging MRI configurations. The accuracy and efficiency of this ROM is demonstrated by performing comparisons against the full order or high fidelity finite element software, showing great performance in terms of computational speed-up, which has major benefits in the optimisation of the design process of new MRI scanners. E-Thesis Swansea MRI, FEM, POD, 3D, finite elements, magneto-mechanics, reduced order modelling, numerical simulation, multiphysics 19 10 2021 2021-10-19 10.23889/SUthesis.58414 ORCiD identifier https://orcid.org/0000-0003-3494-0511 COLLEGE NANME COLLEGE CODE Swansea University Ledger, Paul D. ; Gil, Antonio J. ; Mallett, M. ; Zlotnik, S. Doctoral Ph.D European Comission - Marie Sklodowska-Curie Actions - Innovative Training Network (MSCA-ITN), AdMoRe project; Grant number - 675919 2021-10-19T16:30:08.0951998 2021-10-19T15:12:21.1845906 Faculty of Science and Engineering School of Engineering and Applied Sciences - Uncategorised MARCOS CHOUCINO 1 58414__21229__f96827e5fbde4b04a7678eebe64e9590.pdf Seoane-Choucino_Marcos_PhD_Thesis_Final_Redacted_Signature.pdf 2021-10-19T15:48:57.1152396 Output 14274904 application/pdf E-Thesis – open access true Copyright: The author, Marcos Seoane Choucino, 2020. true eng
title	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
spellingShingle	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD MARCOS CHOUCINO
title_short	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
title_full	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
title_fullStr	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
title_full_unstemmed	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
title_sort	3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD
author_id_str_mv	51039d0f5cc6da720b741bf5fbcb04c9
author_id_fullname_str_mv	51039d0f5cc6da720b741bf5fbcb04c9_***_MARCOS CHOUCINO
author	MARCOS CHOUCINO
author2	MARCOS CHOUCINO
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publishDate	2021
institution	Swansea University
doi_str_mv	10.23889/SUthesis.58414
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description	Magnetic Resonance Imaging (MRI) scanners have become an essential tool in the medi-cal industry due to their ability to produce high resolution images of the human body. To generate an image of the body, MRI scanners combine strong static magnetic fields with transient gradient magnetic fields. The interaction of these magnetic fields with the con-ducting components present in superconducting MRI scanners gives rise to an important problem in the design of new MRI scanners. The transient magnetic fields give rise to the appearance of eddy currents in conducting components. These eddy currents, in turn, result in electromagnetic stresses, which cause the conducting components to deform and vibrate. The vibrations are undesirable as they lead to a deterioration in image quality (with image artefacts) and to the generation of noise, which can cause patient discomfort. The eddy currents, in addition, lead to heat being dissipated and deposited into the cryo-stat, which is filled with helium in order to maintain the coils in a superconducting state. This deposition of heat can cause helium boil off and potentially result in a costly magnet quench. Understanding the mechanisms involved in the generation of these vibrations and the heat being deposited into the cryostat are, therefore, key for a successful MRI scanner design. This involves the solution of a coupled magneto-mechanical problem, which is the focus of this work.In this thesis, a new computational methodology for the solution of three-dimensional (3D) magneto-mechanical coupled problems with application to MRI scanner design is presented. To achieve this, first an accurate mathematical description of the magneto-mechanical coupling is presented, which is based on a Lagrangian formulation and the assumption of small displacements. Then, the problem is linearised using an AC-DC splitting of the fields, and a variational formulation for the solution of the linearised prob-lem in a time-harmonic setting is presented. The problem is then discretised using high order finite elements, where a combination of hierarchical H1 and H(curl) basis func-tions is used. An efficient staggered algorithm for the solution of the coupled system is proposed, which combines the DC and AC stages and makes use of preconditioned iter-ative solvers when appropriate. This finite element methodology is then applied to a set of challenging academic and industrially relevant problems in order to demonstrate its accuracy and efficiency.This finite element methodology results in the accurate and efficient solution of the magneto-mechanical problem of interest. However, in the design stage of a new MRI scanner, this coupled problem must be solved repeatedly for varying model parameters such as frequency or material properties. Thus, even if an efficient finite element solver is available for the solution of the coupled problem, the need for these repeated simulations result in a bottleneck in terms of computational cost, which leads to an increase in design time and its associated financial implications. Therefore, in order to optimise this process, the application of Reduced Order Modelling (ROM) techniques is considered. A ROM based on the Proper Orthogonal Decomposition (POD) method is presented and applied to a series of challenging MRI configurations. The accuracy and efficiency of this ROM is demonstrated by performing comparisons against the full order or high fidelity finite element software, showing great performance in terms of computational speed-up, which has major benefits in the optimisation of the design process of new MRI scanners.
published_date	2021-10-19T04:14:55Z
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score	11.013619

3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD / MARCOS CHOUCINO

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