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

The nuclear spin polarization of Xe-129 can be enhanced by several orders o f magnitude by using optical pumping techniques. The increased sensitivity of xenon NMR has allowed imaging of lungs as well as other in in vivo appli cations. The most critical parameter for efficient delivery of laser-polari zed 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 h uman blood is measured in vitro as a function of blood oxygenation. Interac tions with dissolved oxygen and with deoxyhemoglobin are found to contribut e to the spin-lattice relaxation time of Xe-129 in blood, the latter intera ction having greater effect. Consequently, relaxation times of Xe-129 in de oxygenated blood are shorter than in oxygenated blood. In samples with oxyg enation equivalent to arterial and venous blood, the Xe-129 T(1)s at 37 deg rees 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 Xe-129 spin-lattice relaxation time in blood decrease s at lower temperatures, but the ratio of T-1 in oxygenated blood to that i n deoxygenated blood is the same at 37 degrees C and 25 degrees C. A compet ing ligand has been used to show that xenon binding to albumin contributes to the Xe-129 spin-lattice relaxation in blood plasma, This technique is pr omising for the study of xenon interactions with macromolecules.