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

The exquisite NMR spectral sensitivity and negligible reactivity of hyperpolarized xenon-129 (HP ¹²⁹Xe) make it attractive for a number of magnetic resonance applications; moreover, HP ¹²⁹Xe embodies an alternative to rare and nonrenewable ³He. However, the ability to reliably and inexpensively produce large quantities of HP ¹²⁹Xe with sufficiently high ¹²⁹Xe nuclear spin polarization (P Xₑ) remains a significant challenge—particularly at high Xe densities. We present results from our “open-source” large-scale (∼1 L/h) ¹²⁹Xe polarizer for clinical, preclinical, and materials NMR and MRI research. Automated and composed mostly of off-the-shelf components, this “hyperpolarizer” is designed to be readily implementable in other laboratories. The device runs with high resonant photon flux (up to 200 W at the Rb D ₁ line) in the xenon-rich regime (up to 1,800 torr Xe in 500 cc) in either single-batch or stopped-flow mode, negating in part the usual requirement of Xe cryocollection. Excellent agreement is observed among four independent methods used to measure spin polarization. In-cell P Xₑ values of ∼90%, ∼57%, ∼50%, and ∼30% have been measured for Xe loadings of ∼300, ∼500, ∼760, and ∼1,570 torr, respectively. P Xₑ values of ∼41% and ∼28% (with ∼760 and ∼1,545 torr Xe loadings) have been measured after transfer to Tedlar bags and transport to a clinical 3 T scanner for MR imaging, including demonstration of lung MRI with a healthy human subject. Long “in-bag” ¹²⁹Xe polarization decay times have been measured (T ₁ ∼38 min and ∼5.9 h at ∼1.5 mT and 3 T, respectively)—more than sufficient for a variety of applications.