Exploring hyperpolarized ⁸³Kr by remotely detected NMR relaxometry

For the first time, a hyperpolarized (hp) noble gas with a nuclear electric quadrupole moment is available for high-field nuclear-magnetic-resonance (NMR) spectroscopy and magnetic-resonance imaging. Hp ⁸³Kr (I=92) is generated by spin-exchange optical pumping and separated from the rubidium vapor used in the pumping process. Optical pumping occurs under the previously unstudied condition of high krypton gas densities. Signal enhancements of more than three orders of magnitude compared to the thermal equilibrium Kr83 signal at 9.4 T magnetic-field strength are obtained. The spin-lattice relaxation of ⁸³Kr is caused primarly by quadrupolar couplings during the brief adsorption periods of the krypton atoms on the surrounding container walls and significantly limits the currently obtained spin polarization. Measurements in macroscopic glass containers and in desiccated canine lung tissue at field strengths between 0.05 and 3 T using remotely detected hp ⁸³Kr NMR spectroscopy reveal that the longitudinal relaxation dramatically accelerates as the magnetic-field strength decreases.