Exploring large-scale nuclear spin polarisation physics of xenon-129 for hyperpolarised gas MRI applications

The isotope xenon-129 (129Xe) can be nuclear spin polarised (magnetised) to very high levels by a process known as spin-exchange optical pumping. When inhaled into the lungs while in an MRI scanner, the highly “hyperpolarised” 129Xe enables exquisite visualisation of the airspaces of the lungs and, owing to xenon being soluble in tissue and blood, visualisation of well-perfused organs such as the kidney and brain.

A major challenge in spin-exchange optical pumping physics in the past has being generating 129Xe gas doses rapidly while maintaining sufficiently high nuclear polarisation levels, which is crucially important for (i) routine 129Xe lung imaging to study large patient populations, and (ii) enabling good quality imaging of 129Xe dissolved in blood and tissue for imaging other organs such as brain.

Within this project, the successful PhD student will be given the unique opportunity to research the unexplored fundamental physics of large-scale nuclear spin polarisation physics. The student would have access to three newly-built 129Xe polarisers in our state-of-the art polariser lab within the POLARIS group, and the nature of the work will involve a balance between the theoretical and experimental aspects of nuclear spin polarisation physics and engineering. While the primary focus of this project is to explore the physics of large-scale nuclear spin polarisation physics, there is scope for the successful candidate to work on in vivo and in vitro applications of hyperpolarised 129Xe MRI on the MRI scanners at the University of Sheffield.

The main components of work the student will undertake during this project are
1) Designing computer models to simulate the Rb-129Xe spin-exchange optical pumping physics.
2) Setting up optics apparatus to perform optical spectroscopy and light polarisation measurements.
3) Polariser system optimisation using dedicated NMR hardware/software
4) Performing atomic spectroscopy to probe the D1 and D2 rubidium-85 and rubidium-87 absorption lines and evaluate the hyperfine structure of these levels under different running conditions.
5) Magnetic field simulations and experimental field mapping to optimise the spin-exchange optical pumping efficiency.
6) Faraday rotation experiments to measure absolute rubidium vapour density under polariser operating conditions.
7) Modelling the thermodynamics of gas flow through the spin-exchange optical pumping cell.
8) Testing the best gas mixture to maximise 129Xe polarisation
9) Measuring the fundamental constants that underpin large-scale Rb-129Xe spin-exchange optical pumping and comparing to theoretical models.
10) Ultimately design and building of a new Rb-129Xe system that incorporating theoretical and experimental work undertaken throughout the project.

Upon completion, the student will be specialised in the following physics research areas:
1) Nuclear polarisation
2) Atomic spectroscopy
3) Nuclear and electron magnetic resonance
4) Angular momentum of light
5) Light-matter interactions
6) MRI physics and clinical applications of 129Xe MRI