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

The magnetic polarization of the stable ¹²⁹Xe isotope may be enhanced dramatically by means of optical techniques and, in principle, hyperpolarized ¹²⁹Xe 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 (T₁^tissue) of ¹²⁹Xe 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 ¹²⁹Xe 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 T₁ of ¹²⁹Xe in the lipid emulsion. Measurements on rats, in vivo, at 2.35 T gave T₁^tissue = 3.6 ± 2.1 sec (±SD, n = 6). This method enables quantitative mapping of cerebral blood flow. Magn Reson Med 49:1014–1018, 2003. © 2003 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]