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

Abstract

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 (T1tissue) 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 twocompartment 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 T1tissue = 3.6 ± 2.1 sec (±SD, n = 6). This method enables quantitative mapping of cerebral blood flow. © 2003 Wiley-Liss, Inc.