Advanced spectroscopic imaging techniques for X-nuclei cardiac magnetic resonance imaging

Thesis

Changes to cardiac metabolism are an important component of heart failure. Understanding these metabolic changes is therefore critical to developing treatments for the failing heart, particularly pharmaceuticals, or other interventions, which aim to restore normal metabolism. A combination of hyperpolarized 13C and 31P magnetic resonance spectroscopic imaging (MRSI) enables quantification of both the substrate usage (13C) and energy output (31P) of cardiac metabolism, allowing a full picture of the metabolic state of the heart to be built up.

Both hyperpolarized 13C and 31P MRSI present significant experimental challenges, which I will address, through the use of advanced acquisition and reconstruction techniques, in this thesis.

The main challenges associated with hyperpolarized 13C MRSI are the short transverse relaxation time of the metabolites, necessitating very rapid readouts, the short half-life of hyperpolarization, which requires the full scan to complete in approximately two minutes, and the bolus injection of hyperpolarized material to the patient, which makes the signal intensity highly dynamic. To address these three challenges, I implemented a hybrid multiple/single-shot spiral sequence, with a rapid readout, which enabled the usual trade-off, inherent to multiple-shot spiral readouts, of temporal and spatial resolution (when selecting the number of shots), to be made at reconstruction, rather than acquisition time.

The principal challenge of 31P MRSI however, is achieving adequate SNR. The low SNR of 31P spectroscopy necessitates significant averaging during the acquisition, which extends scan time and precludes high spatial resolution imaging within a reasonable scan time. In this work I implement two compartmentalized reconstruction techniques, SLAM and SLIM, and apply them at both 3 and 7T, before investigating acquisition parameters, which lead to an improvement in SNR and repeatability over the existing technique used in OCMR.

Together these technological advances have extended our ability to quantify metabolism, which will, through their clinical application, enhance our understanding of heart failure.

Authors: Tyler, A

• DOI: 10.5287/ora-m8m4ba7jv
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: 31P; 13C; X-nuclei; cardiac; MRI
• Subjects: Magnetic resonance imaging; Heart--Imaging