Radio Frequency Coil and Pulse Sequence Design for Hyperpolarised Noble Gas MRI of the Human Lungs and Brain

Conventional 1H MRI relies on protons in bodily tissues which are abundant in most organs of the human body whilst the lungs consist mainly of air spaces with a resulting low density of 1H that can be imaged. Hyperpolarised gas (3He and 129Xe) MRI provides solutions to these challenges by imaging the ventilated airspaces and provides clinical sensitivity to lung disease pathophysiology such as ventilation defects, obstructive lung disease, emphysematous alveolar damage, intrapulmonary oxygen quantification, ventilation-perfusion mismatch and interstitial diseases. In addition, xenon is lipophilic, dissolves into the pulmonary bloodstream and is transported to distal organs (such as heart, brain, kidney and liver). Upon reaching the cerebral vasculature, xenon passively diffuses into the brain tissues. 129Xe exhibits a wide chemical shift range, providing contrast for different compartments of the brain (such as grey matter, white matter, cerebrospinal fluid and blood). Using LASER spin exchange optical pumping, the NMR sensitivity of hyperpolarised gases is dramatically increased allowing the detection at very low concentrations.

In this thesis, I have developed original instrumentation for new applications of hyperpolarised gas MRI in lungs and brain and make novel research contributions in order to;

(a) Improve the signal-to-noise ratio of 1H signal from the lungs in multi-nuclear same-breath lung imaging, by establishing an accurate analytical method to design a 1H receiver coil array that functions nested inside a 3He or 129Xe transmit-receive coil.

(b) Demonstrate triple-nuclear (129Xe-3He-1H) same-breath lung imaging (structure-ventilation) and dual-nuclear (129Xe-3He) same-breath apparent diffusion coefficient mapping with a new dual tuned RF transceiver coil design.

(c) Demonstrate the feasibility of using hyperpolarized 129Xe for in vivo evaluation of cerebral perfusion and, using tracer kinetic analysis, enable quantitative measurement of the intrinsic properties of the blood-brain barrier.