Enabling Clinical Technologies for Hyperpolarized Xenon-129 MRI and Spectroscopy

Hyperpolarization is a technique that can increase nuclear spin polarization with the corresponding gains in nuclear magnetic resonance (NMR) signal by 4–8 orders of magnitude. By applying this process to biologically relevant samples, they can be used as exogenous MRI contrast agents. A technique called Spin Exchange Optical Pumping (SEOP) can be applied to hyperpolarize noble gases such as 129 Xe. Hyperpolarized 129 Xe is poised to revolutionize clinical lung imaging, offering a non-ionizing, high contrast alternative to CT imaging and conventional proton MRI. Moreover, CT and conventional proton MRI report on lung tissue structure but provide no functional information although substantial progress has been made recently using ultrashort (UTE) TE MRI to obtain surrogate ventilation metrics. On the other hand, by breathing hyperpolarized 129 Xe gas, strong MRI signal can be obtained to produce functional lung images reporting on lung ventilation, perfusion and diffusion with 3D readout in seconds. In this Review, the physics of SEOP is discussed and the different production modalities are explained in the context of their clinical application. We also briefly compare SEOP to other hyperpolarization methods and conclude this paper with the biomedical outlook for hyperpolarized 129 Xe applications to lung imaging and beyond. Hyperpolarized 129 Xe has a potential to revolutionize clinical imaging, offering a non-ionizing contrast of organ function complementary to the CT imaging and to conventional MRI. Here, the spin physics of SEOP is discussed and the different production modalities are explained in the context of their clinical application. We conclude with the biomedical outlook for hyperpolarized 129 Xe applications to lung imaging and beyond.