Optical hyperpolarization of noble gases for medical imaging

Magnetic resonance imaging (MRI) of human or animal lungs became possible with the application of hyperpolarized noble gases, such as ^{3}He or ^{129}Xe. This method allows obtaining information on lung morphology and functionality. Introduction of hyperpolarized noble gases provided as well a new tool for non-medical applications such as neutron filters or nuclear magnetic resonance (NMR) spectroscopy studies in porous materials. The high polarization of noble gases is possible using so-called optical pumping methods. In this chapter the two most common polarization techniques of noble gases (^{3}He and ^{129}Xe), spin exchange optical pumping (SEOP) and metastability exchange optical pumping (MEOP) are presented. Variations of these methods delivering higher ^{3}He and ^{129}Xe polarization including hybrid SEOP or MEOP in standard conditions and in elevated pressure and high magnetic fields are also reported. A short description of the equipment used for gas polarization is also provided