Longitudinal nuclear spin relaxation of 129Xe in solution and in hollow fiber membranes at low and high magnetic field strengths
To measure dissolved-phase 129Xe T1 values at high and low magnetic fields and the field dependence of 129Xe depolarization by hollow fiber membranes used to infuse hyperpolarized xenon in solution.
Dissolved-phase T1 measurements were made at 11.7T and 2.1 mT by bubbling xenon in solution and by using a variable delay to allow spins to partially relax back to thermal equilibrium before probing their magnetization. At high field, relaxation values were compared to those obtained by using the small flip angle method. For depolarization studies, we probed the magnetization of the polarized gas diffusing through an exchange membrane module placed at different field strengths.
Total loss of polarization was observed for xenon diffusing through hollow fiber membranes at low field, while significant polarization loss (>20%) was observed at magnetic fields up to 2T. Dissolved-phase 129Xe T1 values were found consistently shorter at 2.1 mT compared to 11.7T. In addition, both O2 and Xe gas concentrations in solution were found to significantly affect dissolved-phase 129Xe T1 values.
Dissolved-phase 129Xe measurements are feasible at low field, but to assess the feasibility of in vivo dissolved-phase imaging and spectroscopy the T1 of xenon in blood will need to be measured. Both O2 and Xe concentrations in solution are found to greatly affect dissolved-phase 129Xe T1 values and may explain, along with RF miscalibration, the large discrepancy in previously reported results.