Measurements of the persistent singlet state of N2O in blood and other solvents—Potential as a magnetic tracer

The development of hyperpolarized tracers has been limited by short nuclear polarization lifetimes. The dominant relaxation mechanism for many hyperpolarized agents in solution arises from intramolecular nuclear dipole–dipole coupling modulated by molecular motion. It has been previously demonstrated that nuclear spin relaxation due to this mechanism can be removed by storing the nuclear polarization in long‐lived, singlet‐like states. In the case of N2O, storing the polarization of the nitrogen nuclei has been shown to substantially increase the polarization lifetime. The feasibility of utilizing N2O as a tracer is investigated by measuring the singlet‐state lifetime of the N2O when dissolved in a variety of solvents including whole blood. Comparison of the singlet lifetime to longitudinal relaxation and between protonated and deuterated solvents is consistent with the dominance of spin‐rotation relaxation, except in the case of blood. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.