Computational approaches to parallel transmission MRI
This thesis is concerned with the design of spatially-selective RF pulses accelerated by parallel transmission. These pulses perturb the magnetisation in an object within a 2D or 3D sub-volume, whilst leaving magnetisation outside of these regions unaffected. As such, they are shown to be useful in...
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| Format: | Thesis (University of Nottingham only) |
| Language: | English |
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2020
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| Online Access: | https://eprints.nottingham.ac.uk/60871/ |
| _version_ | 1848799816227749888 |
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| author | Mirfin, Christopher |
| author_facet | Mirfin, Christopher |
| author_sort | Mirfin, Christopher |
| building | Nottingham Research Data Repository |
| collection | Online Access |
| description | This thesis is concerned with the design of spatially-selective RF pulses accelerated by parallel transmission. These pulses perturb the magnetisation in an object within a 2D or 3D sub-volume, whilst leaving magnetisation outside of these regions unaffected. As such, they are shown to be useful in certain dynamic field-shimming strategies.
The first chapter reviews the equation of motion for a magnetisation vector and alternative compact formulations; electromagnetic fields in tissue at 7 T; requisite imaging sequences; and some numerical and computational methods.
The second chapter reviews some existing design strategies and capabilities of parallel transmission (PTx). It also includes a derivation of the adiabatic condition, which is critical for the design of frequency-modulated pulses.
In Chapter 3 the design of short PTx pulses with optimised k-space trajectories to excite an arbitrary 3d volume is presented. As part of this, the parameterisation of the excitation k-space trajectory is considered under alternative linear transformations subject to realistic gradient performance. A GPU is used to reduce computational time of an existing local and a novel second global optimisation algorithm.
In Chapter 4 a novel acquisition strategy is developed and implemented to improve the overall static field homogeneity by utilising reduced field of excitation with acceleration via parallel transmission in conjunction with dynamic first-order local shimming.
In the preceding chapters the use and design of spatially-selective RF pulses was strictly limited to amplitude-modulated waveforms. In Chapter 5 a spatially-selective FM pulse that is resilient to a level of transmit-field inhomogeneity is implemented. An optimisation scheme is sought that exploits the adiabatic condition to relax the spatial transmit-field magnitude and phase patterns.
Chapter 6 discusses the work presented in this thesis, and highlights possible directions for future projects.
An Appendix is appended to this thesis, highlighting a software application that was developed to ameliorate some of the experimental workflow challenges associated with pTx. |
| first_indexed | 2025-11-14T20:41:40Z |
| format | Thesis (University of Nottingham only) |
| id | nottingham-60871 |
| institution | University of Nottingham Malaysia Campus |
| institution_category | Local University |
| language | English |
| last_indexed | 2025-11-14T20:41:40Z |
| publishDate | 2020 |
| recordtype | eprints |
| repository_type | Digital Repository |
| spelling | nottingham-608712025-02-28T14:57:15Z https://eprints.nottingham.ac.uk/60871/ Computational approaches to parallel transmission MRI Mirfin, Christopher This thesis is concerned with the design of spatially-selective RF pulses accelerated by parallel transmission. These pulses perturb the magnetisation in an object within a 2D or 3D sub-volume, whilst leaving magnetisation outside of these regions unaffected. As such, they are shown to be useful in certain dynamic field-shimming strategies. The first chapter reviews the equation of motion for a magnetisation vector and alternative compact formulations; electromagnetic fields in tissue at 7 T; requisite imaging sequences; and some numerical and computational methods. The second chapter reviews some existing design strategies and capabilities of parallel transmission (PTx). It also includes a derivation of the adiabatic condition, which is critical for the design of frequency-modulated pulses. In Chapter 3 the design of short PTx pulses with optimised k-space trajectories to excite an arbitrary 3d volume is presented. As part of this, the parameterisation of the excitation k-space trajectory is considered under alternative linear transformations subject to realistic gradient performance. A GPU is used to reduce computational time of an existing local and a novel second global optimisation algorithm. In Chapter 4 a novel acquisition strategy is developed and implemented to improve the overall static field homogeneity by utilising reduced field of excitation with acceleration via parallel transmission in conjunction with dynamic first-order local shimming. In the preceding chapters the use and design of spatially-selective RF pulses was strictly limited to amplitude-modulated waveforms. In Chapter 5 a spatially-selective FM pulse that is resilient to a level of transmit-field inhomogeneity is implemented. An optimisation scheme is sought that exploits the adiabatic condition to relax the spatial transmit-field magnitude and phase patterns. Chapter 6 discusses the work presented in this thesis, and highlights possible directions for future projects. An Appendix is appended to this thesis, highlighting a software application that was developed to ameliorate some of the experimental workflow challenges associated with pTx. 2020-07-24 Thesis (University of Nottingham only) NonPeerReviewed application/pdf en arr https://eprints.nottingham.ac.uk/60871/1/Mirfin2019_corrected.pdf Mirfin, Christopher (2020) Computational approaches to parallel transmission MRI. PhD thesis, University of Nottingham. MRI Parallel transmission |
| spellingShingle | MRI Parallel transmission Mirfin, Christopher Computational approaches to parallel transmission MRI |
| title | Computational approaches to parallel transmission MRI |
| title_full | Computational approaches to parallel transmission MRI |
| title_fullStr | Computational approaches to parallel transmission MRI |
| title_full_unstemmed | Computational approaches to parallel transmission MRI |
| title_short | Computational approaches to parallel transmission MRI |
| title_sort | computational approaches to parallel transmission mri |
| topic | MRI Parallel transmission |
| url | https://eprints.nottingham.ac.uk/60871/ |