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Title: Computational approaches to parallel transmission MRI
Author: Mirfin, Christopher
ISNI:       0000 0004 9350 6042
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2020
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC501 Electricity and magnetism