Hyperpolarized129XeT1 in oxygenated and deoxygenated blood

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Abstract
The viability of the new technique of hyperpolarized 129Xe MRI (HypX‐MRI) for imaging organs other than the lungs depends on whether the spin–lattice relaxation time, T1, of 129Xe is sufficiently long in the blood. In previous experiments by the authors, the T1 was found to be strongly dependent upon the oxygenation of the blood, with T1 increasing from about 3 s in deoxygenated samples to about 10 s in oxygenated samples. Contrarily, Tseng et al. (J. Magn. Reson. 1997; 126: 79–86) reported extremely long T1 values deduced from an indirect experiment in which hyperpolarized 129Xe was used to create a ‘blood‐foam’. They found that oxygenation decreasedT1. Pivotal to their experiment is the continual and rapid exchange of hyperpolarized 129Xe between the gas phase (within blood‐foam bubbles) and the dissolved phase (in the skin of the bubbles); this necessitated a complicated analysis to extract the T1 of 129Xe in blood. In the present study, the experimental design minimizes gas exchange after the initial bolus of hyperpolarized 129Xe has been bubbled through the sample. This study confirms that oxygenation increases the T1 of 129Xe in blood, from about 4 s in freshly drawn venous blood, to about 13 s in blood oxygenated to arterial levels, and also shifts the red blood cell resonance to higher frequency. Copyright © 2000 John Wiley & Sons, Ltd. Abbreviations used BOLD blood oxygen level dependent NOE nuclear overhouses effect PO2 oxygen partial pressure RBC red blood cells RF radio frequency SNR signal‐to‐noise ratio.

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