ACCELERATING EDITED MAGNETIC RESONANCE SPECTROSCOPY AND SPECTROSCOPIC IMAGING OF THE HUMAN BRAIN AT 3T
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Date
2019-03-23
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Johns Hopkins University
Abstract
Edited magnetic resonance spectroscopy is a method capable of probing biochemical processes non-invasively, but suffers from an inherently low signal-to-noise which results in long acquisition times. Increasing the efficiency of these scans would reduce these acquisition times and can increase the number of scans, and consequently the amount of information, that can be acquired within a time-limited scan session in clinical and research settings.
This thesis addresses this need with methods to increase the number of metabolites and regions that can be detected within a single scan as well as a method to reduce the duration of the preparation pulses. In particular, we demonstrate the ability of two techniques to detected glutathione and lactate simultaneously. We then move on to introduce ‘Hadamard Encoding and Reconstruction of MEGA-Edited Spectroscopy’ (HERMES) and demonstrate that it can detect two and three metabolites simultaneously. As an example of this method, a scheme for separately detecting N-acetylaspartate (NAA) and N-acetylaspartylglutamate (NAAG) is presented. This scheme is then extended to separately edit Aspartate in addition to NAA and NAAG. All multi-metabolite editing schemes are shown to be capable of optimally detecting each metabolite separately in simulations, phantom, and in vivo experiments. Relative to separate acquisitions of each metabolite separately, multi-metabolite editing results in a scan time reduction of two-fold and three-fold for editing two metabolites and three metabolites respectively.
This thesis then introduces and evaluates methods for multi-region editing. First, a new technique ‘Spatial Hadamard Editing and Reconstruction for Parallel Acquisition’ (SHERPA) is introduced and found to be capable of separating the GABA-edited spectra from two voxels. HERMES is then extended for use with magnetic resonance spectroscopic imaging (MRSI) and is found to be also introduced and is shown to decrease subtraction artifacts in GABA-edited spectra. Lastly, a short-duration water suppression technique compatible for use with fast editedMRSI sequences is introduced and is shown to suppress water better than VAPOR.
Readers: Peter Barker, DPhil and Richard Edden, PhD
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Keywords
brain, simultaneous, NAA, NAAG, Asp, GABA, Glutathione, Lactate, spectral editing, magnetic resonance spectroscopy, hadamard