Batch-Mode Clinical-Scale Optical Hyperpolarization of Xenon-129 Using an Aluminum Jacket with Rapid Temperature Ramping

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (∼170 W) pump laser irradiation and a novel aluminum jacket design for rapid temperature ramping of xenon-rich gas mixtures (up to 2 atm partial pressure). The aluminum jacket design is capable of heating SEOP cells from ambient temperature (typically 25 °C) to 70 °C (temperature of the SEOP process) in 4 min, and perform cooling of the cell to the temperature at which the hyperpolarized gas mixture can be released from the hyperpolarizer (with negligible amounts of Rb metal leaving the cell) in approximately 4 min, substantially faster (by a factor of 6) than previous hyperpolarizer designs relying on air heat exchange. These reductions in temperature cycling time will likely be highly advantageous for the overall increase of production rates of batch-mode (i.e., stopped-flow) 129Xe hyperpolarizers, which is particularly beneficial for clinical applications. The additional advantage of the presented design is significantly improved thermal management of the SEOP cell. Accompanying the heating jacket design and performance, we also evaluate the repeatability of SEOP experiments conducted using this new architecture, and present typically achievable hyperpolarization levels exceeding 40% at exponential build-up rates on the order of 0.1 min–1

EXPERIMENTAL ADVANCES IN CLINICAL-SCALE PRODUCTION OF HYPERPOLARIZED 129XE AND 131XE VIA STOPPED-FLOW SPIN-EXCHANGE OPTICAL PUMPING

Spin-exchange optical pumping (SEOP) produces hyperpolarized noble gases (e.g. 129Xe and 131Xe) that have been used to improve spatial resolution and speed of biological magnetic resonance imaging, enhance NMR signals of molecules and materials, and utilized in fundamental physics experiments. In SEOP, circularly polarized laser light optically pumps an alkali metal vapor (e.g. Cs or Rb) into an electronically spin-polarized ground state. This electronic spin polarization can then be transferred to the nucleus of a noble gas during gas phase collisions. Over time, a bulk nuclear spin polarization begins to accumulate, resulting in hyperpolarized (HP) gases. The research presented in this thesis is concerned with the optimization of experimental aspects in clinical-scale HP 129Xe and high-density HP 131Xe production by stopped-flow SEOP—specifically with respect to alkali metal choice, laser technology, SEOP cell design and experimental conditions. This thesis is divided into five main chapters. The first chapter is written to provide an introduction into the field of NMR, giving both historical context and relevant NMR phenomenon to help understand nuclear spin hyperpolarization. The second chapter gives a brief introduction into SEOP and how the evolution of laser technology has given rise to current methodologies. Secondly, this chapter includes a brief summary of SEOP theory as well as mathematically outlines the process of how electron spin polarization via optical pumping leads to long-lived nuclear spin polarizations via spin-exchange. Furthermore, this chapter provides a description of the stopped-flow (i.e. batch-mode) SEOP setup and how in situ measurements of HP noble gases are made. Chapters 3 and 4 are concerned with hyperpolarization of 129Xe and 131Xe, respectively. In both of these chapters, the physical and chemical properties of the respective isotope of xenon are given followed by how to calculate their bulk nuclear spin polarizations using in situ measurements. Exploration to the changes in experimental conditions (i.e. alkali metal choice, temperature, laser technology, etc.) allowed for a comparison of the resulting spin dynamics and polarizations to be made in both chapters. In addition, Chapter 3 includes a brief description of the continuing efforts to implement an aluminum optical pumping cell for use in SEOP. Finally, Chapter 5 will cover preliminary work towards transferring the polarization from HP 129Xe to that of a target molecule. While other groups have shown that this ‘xenon induced polarization’ is possible, we have yet to replicate this phenomenon; However, Chapter 5 will show our work towards ex situ measurements of HP 129Xe and how this will act as a stepping stone towards transferring the polarization to a target molecule