On the oxygenation-dependent Xe-129 T-1 in blood

The spin-lattice relaxation time, T-1, of hyperpolarized Xe-129 in blood is sensitive to blood oxygenation. In particular, it has been shown that Xe-1 29 T-1 is shorter in venous blood than in arterial blood. We have studied t he T-1 of hyperpolarized Xe-129 dissolved in human blood as a function of b rood oxygenation level, sO(2), in the physiological oxygenation range. We s how that the Xe-129 relaxation rate, T-1(-1) varies in a nonlinear fashion as a function of SO2 This finding suggests that direct interaction of xenon with the paramagnetic heme group of deoxyhemoglobin is not the dominant ox ygenation-dependent relaxation mechanism for Xe-129 in blood. These results corroborate the idea that the oxygenation-dependence of Xe-129 T-1 is dete rmined by conformational changes of hemoglobin induced by oxygen binding. C opyright (C) 2000 John Wiley Br Sons, Ltd.