T1 of 129Xe in blood and the role of oxygenation

In previous experiments by the authors, in which hyperpolarized Xe-129 was dissolved in fresh blood samples, the T-1 was found to be strongly dependent on the oxygenation level, the values increasing with oxygenation: T-1 was about 4 s in deoxygenated samples and about 13 s in oxygenated samples. C. H. Tseng et al. (1997, J. Magn. Reson. 126, 79-86), on the other hand, recently reported extremely long T-1 values using hyperpolarized Xe-129 to create a "blood foam" and found that oxygenation decreased T-1. In their experiments, the continual and rapid exchange of hyperpolarized Xe-129 between the gas phase (within blood-foam bubbles) and the dissolved phase tin the skin of the bubbles) necessitated a complicated analysis to extract the effective blood T-1. In the present study, the complications of hyperpolarized Xe-129 exchange dynamics have been avoided by using thermally polarized Xe-129 dissolved in whole blood and in suspensions of lysed red blood cells (RBC). During T-1 measurements in whole blood, the samples were gently and continuously agitated, for the entire course of the experiment, to avert sedimentation. Oxygenation was found to markedly increase the T-1 of Xe-129 in blood, as originally measured, and it shifts the RBC resonance to a higher frequency. Carbon monoxide has a similar but somewhat stronger effect. (C) 1999 Academic Press.