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

In this work, the production rate of a spin-exchange optical pumping Xe-129 gas polarizer was optimized for routine generation of hyperpolarized Xe-129 for in vivo lung MRI. This system uses a narrow (similar to 0.1 nm linewidth), tuneable external cavity laser (operating at similar to 25W) for SEOP of 3% gas mixtures of Xe inside a mid-pressure (2 bars) cell of 491 cm(3) volume. Under this regime, theoretical and experimentally measured (129) Xe 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 T-1 of 87 +/- 2 min was observed. To demonstrate the system's application, in vivo lung magnetic resonance images (signal-to-noise ratio similar to 50 from a voxel of 15 mm x 4 mm x 4 mm) were acquired using modest volumes (<400ml) of isotopically enriched (86% Xe-129) 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 Xe-129 lung imaging studies. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4776763]