Optimized production of hyperpolarized 129Xe at 2 bars for in vivo lung magnetic resonance imaging

Abstract

In this work, the production rate of a spin-exchange optical pumping 129Xe gas polarizer was optimized for routine generation of hyperpolarized 129Xe for in vivo lung MRI. This system uses a narrow (∼ 0.1 nm linewidth), tuneable external cavity laser (operating at ∼25 W) for SEOP of 3% gas mixtures of Xe inside a mid-pressure (2 bars) cell of 491 cm3 volume. Under this regime, theoretical and experimentally measured 129Xe polarizations were calculated to be 24% and 12%, respectively, for a gas flow rate of 300 sccm and a cell temperature of 373 K. The photon efficiency was evaluated, yielding theoretical and experimental values of 0.039 and 0.046, respectively. The theoretical efficiency was calculated from spin-exchange and spin-destruction cross sections and the experimental photon efficiency was measured under flow for a gas-cell residency time equal to an empirically determined spin-exchange time of 45 s. In addition, details of the Xe freeze-out process were analyzed with a model of polarization decay during Xe accumulation in the frozen phase, where a T1 of 87 ± 2 min was observed. To demonstrate the system's application, in vivo lung magnetic resonance images (signal-to-noise ratio ∼ 50 from a voxel of 15 mm× 4 mm× 4 mm) were acquired using modest volumes (<400 ml) of isotopically enriched (86% 129Xe) Xe gas polarized to >10%. Despite the experimental polarization being a factor of 2 lower than the predicted polarization for typical operating parameters, the system is close to the theoretical photon efficiency and the system has so far produced polarized gas for more than 100 in vivo 129Xe lung imaging studies.

Characterizing and modeling the efficiency limits in large-scale production of hyperpolarizedXe129

“…A means to model the SEOP process was introduced by Wagshul and Chupp [27] in 1989, and was recently updated by Norquay, et al to include the latest measured spin exchange and spin destruction cross-sections for 129 Xe [16]. We use this as the “standard model” with two minor changes (see Appendix).…”

“…As introduced by Bhaskar, et al [14], the fraction of Rb- 129 Xe collisions resulting in spin exchange rather than alkali spin destruction, determines the overall efficiency with which circularly polarized photons are converted into nuclear spins. This so-called photon efficiency for 129 Xe-Rb spin exchange during binary collisions and short-lived molecular formation [15] was recently re-calculated by Norquay, et al [16] to be 4.6%. That is, for every Watt of 795 nm light absorbed by the 129 Xe-Rb system, it should be feasible to produce 25 mL/hr of polarized 129 Xe.…”

Molecular hydrogen and catalytic combustion in the production of hyperpolarized 83 Kr and 129 Xe 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).…”

A method for measuring the spin polarization of 129Xe by using an atomic magnetometer

“…The high spin polarization of hyperpolarized noble gases finds applications in a number of fields, including Magnetic Resonance Imaging (MRI), [1][2][3] neutron spin filters, 4,5 optical atomic magnetometers, [6][7][8] spin precession gyroscopes, 9,12 and devices aimed at studying fundamental physics. 10,11 In all these applications, the spin polarization of the 129 Xe nuclei influences the detection sensitivity and the Signal-to-Noise Ratio (SNR) of the devices.…”