Spin-lattice relaxation of laser-polarized xenon in human blood

The nuclear spin polarization of (129)Xe can be enhanced by several orders of magnitude by using optical pumping techniques. The increased sensitivity of xenon NMR has allowed imaging of lungs as well as other in vivo applications. The most critical parameter for efficient delivery of laser-polarized xenon to blood and tissues is the spin-lattice relaxation time (T(1)) of xenon in blood. In this work, the relaxation of laser-polarized xenon in human blood is measured in vitro as a function of blood oxygenation. Interactions with dissolved oxygen and with deoxyhemoglobin are found to contribute to the spin-lattice relaxation time of (129)Xe in blood, the latter interaction having greater effect. Consequently, relaxation times of (129)Xe in deoxygenated blood are shorter than in oxygenated blood. In samples with oxygenation equivalent to arterial and venous blood, the (129)Xe T(1)s at 37°C and a magnetic field of 1.5 T were 6.4 s ± 0.5 s and 4.0 s ± 0.4 s, respectively. The (129)Xe spin-lattice relaxation time in blood decreases at lower temperatures, but the ratio of T(1) in oxygenated blood to that in deoxygenated blood is the same at 37°C and 25°C. A competing ligand has been used to show that xenon binding to albumin contributes to the (129)Xe spin-lattice relaxation in blood plasma. This technique is promising for the study of xenon interactions with macromolecules.