Cryogenics free production of hyperpolarized ¹²⁹Xe and ⁸³Kr for biomedical MRI applications

As an alternative to cryogenic gas handling, hyperpolarized (hp) gas mixtures were extracted directly from the spin exchange optical pumping (SEOP) process through expansion followed by compression to ambient pressure for biomedical MRI applications. The omission of cryogenic gas separation generally requires the usage of high xenon or krypton concentrations at low SEOP gas pressures to generate hp ¹²⁹Xe or hp ⁸³Kr with sufficient MR signal intensity for imaging applications. Two different extraction schemes for the hp gasses were explored with focus on the preservation of the nuclear spin polarization. It was found that an extraction scheme based on an inflatable, pressure controlled balloon is sufficient for hp ¹²⁹Xe handling, while ⁸³Kr can efficiently be extracted through a single cycle piston pump. The extraction methods were tested for ex vivo MRI applications with excised rat lungs. Precise mixing of the hp gases with oxygen, which may be of interest for potential in vivo applications, was accomplished during the extraction process using a piston pump. The ⁸³Kr bulk gas phase T₁ relaxation in the mixtures containing more than approximately 1% O₂ was found to be slower than that of ¹²⁹Xe in corresponding mixtures. The experimental setup also facilitated ¹²⁹Xe T₁ relaxation measurements as a function of O₂ concentration within excised lungs.