Method to determine in vivo the relaxation time T1 of hyperpolarized xenon in rat brain

The magnetic polarization of the stable Xe-129 isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized Xe-129 MRI should allow quantitative mapping of cerebral blood flow with better spatial resolution than scintigraphic techniques. A parameter necessary for this quantitation, and not previously known, is the longitudinal relaxation time, (T-1(tissue)) of Xe-129 in brain tissue in vivo: a method for determining this is reported. The time course of the MR signal in the brain during arterial injection of hyperpolarized Xe-129 in a lipid emulsion was analyzed using an extended two-compartment model. The model uses experimentally determined values of the RF flip angle and the T-1 of Xe-129 in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T-1(tissue) = 3.6 +/- 2.1 sec (+/-SD, n = 6). This method enables quantitative mapping of cerebral blood flow. (C) 2003 Wiley-Liss, Inc.