Abstract
We present a new method for the continuous flow production of concentrated hyperpolarized xenon-129 (HP 129Xe) gas from a dilute xenon (Xe) gas mixture with high nuclear spin polarization. A low vapor pressure (i.e., high boiling-point) gas was introduced as an alternative to molecular nitrogen (N2), which is the conventional quenching gas for generating HP 129Xe via Rb-Xe spin-exchange optical-pumping (SEOP). In contrast to the generally used method of extraction by freezing Xe after the SEOP process, the quenching gas separated as a liquid at moderately low temperature so that Xe was maintained in its gaseous state, allowing the continuous delivery of highly polarized concentrated Xe gas. We selected isobutene as the candidate quenching gas and our method was demonstrated experimentally while comparing its performance with N2. Isobutene could be liquefied and removed from the Xe gas mixture using a cold trap, and the concentrated HP 129Xe gas exhibited a significantly enhanced nuclear magnetic resonance (NMR) signal. Although the system requires further optimization depending on the intended purpose, our approach presented here could provide a simple means for performing NMR or magnetic resonance imaging (MRI) measurements continuously using HP 129Xe with improved sensitivity.
Highlights
Nuclear magnetic resonance (NMR) of hyperpolarized xenon-129 (HP 129Xe) atoms has been widely used in a variety of research areas, such as physics, chemistry, material science, and biomedical imaging[1, 2]
The only effective way to concentrate HP 129Xe for further use in nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) is freeze-thaw separation, in which Xe in the continuously flowing gas mixture is frozen and accumulated until it reaches a sufficient amount for use, and the solid Xe is thawed to return it to a gaseous state[8, 10, 11, 14, 15]
Our proposal for concentrating HP 129Xe gas from a dilute Xe gas mixture was to use a high boiling point gas as a quenching gas that condenses at a higher temperature than Xe
Summary
Nuclear magnetic resonance (NMR) of hyperpolarized xenon-129 (HP 129Xe) atoms has been widely used in a variety of research areas, such as physics, chemistry, material science, and biomedical imaging[1, 2]. HP 129Xe gas is usually produced via a spin-exchange optical-pumping (SEOP) method, in which a hyperpolarized nuclear spin state is achieved based on the transfer of the angular momentum carried by photons from circularly polarized laser light[3, 4]. Because Xe freezes well above the boiling point of both N2 and He, the buffer gases can be removed by freezing out the Xe. At present, the only effective way to concentrate HP 129Xe for further use in NMR or magnetic resonance imaging (MRI) is freeze-thaw separation, in which Xe in the continuously flowing gas mixture is frozen and accumulated until it reaches a sufficient amount for use, and the solid Xe is thawed to return it to a gaseous state[8, 10, 11, 14, 15]. Its use is limited to NMR or MRI experiments conducted in a batch mode
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