Characterization of a low-pressure high-capacityX129eflow-through polarizer

Abstract

We describe a low-pressure flow-through apparatus for generating hyperpolarized 129 Xe and report its performance by examining both the output 129 Xe polarization P Xe by NMR and the in situ Rb polarization profile by optically detected electron paramagnetic resonance. The polarizer is based on a previously presented design employing a long optical pumping cell, lean Xe mixture at low pressure, Rb presaturation, and counterflow of gas with respect to the direction of light propagation. The numerical model to which we compare the polarizer's performance includes the temperature dependence of the Rb-129 Xe spin-exchange rate, which has not previously been treated. The qualitative trends in the data mostly follow those in the model, although the model predicts P Xe to be up to a factor of two higher than observed. This discrepancy cannot be attributed to low Rb polarization: the model and the optically detected electron paramagnetic resonance data ͑acquired at six points along the length of the heated portion of the optical pumping cell͒ are in reasonable agreement and show typical values of 85%-95%, although measurements also reveal an anomalous region of depressed Rb polarization near the middle of the cell. The highest output 129 Xe polarization P Xe =84Ϯ 16%, was recorded using Ϸ60 W of frequency-narrowed laser light at a Xe partial pressure ͑referenced to 20°C͒ of 1.1Ϯ 0.2 mbar, flowing at 1 sccm of Xe; typical values were P Xe Ϸ 20% flowing at 10 sccm of Xe with Ϸ30 W of laser light.

Near-unity nuclear polarization with an open-source 129 Xe hyperpolarizer for NMR and MRI

“…In many applications, HP 129 Xe can replace 3 He, and the relative abundance of 129 Xe can greatly reduce the impact of the worldwide 3 He shortage (13) in these instances. Despite considerable progress (14)(15)(16)(17)(18)(19)(20)(21)(22), a major obstacle toward implementing HP 129 Xe for clinical imaging has been the ability to reliably and inexpensively produce large quantities of HP 129 Xe with high polarization (P Xe ). † HP 129 Xe is usually created via spin-exchange optical pumping (SEOP) (23), whereby the unpaired electronic spins of an alkali metal vapor (e.g., Rb) are polarized via optical pumping with circularly polarized light, and the polarization is transferred to noble gas nuclear spins during collisions.…”

Molecular hydrogen and catalytic combustion in the production of hyperpolarized83Kr and129Xe MRI contrast agents

“…Technological improvements (6)(7)(8)(9)(10)(11)(12)(13)(14)(15) have enabled pulmonary hp 129 Xe MRI at high spatial resolution, thereby reducing the need for use of the scarcely available 3 He isotope. Furthermore, tissue solubility, large chemical shift range, and interaction with specific sensor molecules allow for a variety of hp 129 Xe applications in biomedical sciences and beyond (1-6, 16, 17).…”

Robust solidXe129longitudinal relaxation times

“…3. In brief, a gas mixture lean in naturally abundant xenon (Linde) was allowed to flow upward through a long vertically oriented cylindrical glass optical pumping cell (1 m long by 10 cm dia).…”

“…An effective and widely used methodology [1][2][3] for producing large quantities of hyperpolarized 129 Xe includes cryogenic condensation, accumulation, and storage in the solid state of 129 Xe gas polarized by spinexchange optical pumping [4] in a large magnetic field (a few kilogauss or greater). Despite recent progress in improving gas-phase storage methods [5][6][7], almost all commercial and home-built xenon polarizers employ cryogenic storage in a flow-through system.…”