Take a breath of polarized noble gas

I sn't that title just a piece of nonsense designed to catch your attention? Why should you breathe in the inert noble gas knowing that you need oxygen instead? Maybe an aging singer could mix some helium to his breath when his voice does not meet the high notes anyrnore. Of course, divers exchange nitrogen with helium since even under pressure it hardly dissolves in the blood and hence averts the danger ofbubbling and embolism when the pressure is released. But do not mix it up with a xenon bottle! You would quickly lose your consciousness, since xenon penetrates into the blood and further into the brain with anaesthetizing effect. The real trick, however, is breathing spin-polarized noble gas! Why? Almost a decade ago, a Princeton-StonyBrook collaboration published a seminal paper in NATURE [1] in which they showed for the first time a magnetic resonance image (MRI) of excised mouse lungs filled with spin-polarized 129Xe (Fig. 1 left). The image was not formed as usual from the MRI signal of the protons in the tissue but from the pre-polarized xenon nuclei serving as a contrast agent, so to say. The decisive novelty in MRI was the use of spins which had been pre-polarized beforehand to a so-called hyperpolarization far beyond thermal equilibrium. In contrast the usual MRI signal derives from the Boltzmann polarization Pa ofnuclear spins, which is established in the magnetic field Boof the tomograph within a so-called longitudinal relaxation time T1 oforder Is to the thermal equilibrium value of