High resolution spectroscopy and chemical shift imaging of hyperpolarized <sup>129</sup> Xe dissolved in the human brain in vivo at 1.5 tesla
Purpose
Upon inhalation, xenon diffuses into the bloodstream and is transported to the brain, where it dissolves in various compartments of the brain. Although up to five chemically distinct peaks have been previously observed in 129Xe rat head spectra, to date only three peaks have been reported in the human head. This study demonstrates high resolution spectroscopy and chemical shift imaging (CSI) of 129Xe dissolved in the human head at 1.5 Tesla.

Methods
A 129Xe radiofrequency coil was built in-house and 129Xe gas was polarized using spin-exchange optical pumping. Following the inhalation of 129Xe gas, NMR spectroscopy was performed with spectral resolution of 0.033 ppm. Two-dimensional CSI in all three anatomical planes was performed with spectral resolution of 2.1 ppm and voxel size 20 mm × 20 mm.

Results
Spectra of hyperpolarized 129Xe dissolved in the human head showed five distinct peaks at 188 ppm, 192 ppm, 196 ppm, 200 ppm, and 217 ppm. Assignment of these peaks was consistent with earlier studies.

Conclusion
High resolution spectroscopy and CSI of hyperpolarized 129Xe dissolved in the human head has been demonstrated. For the first time, five distinct NMR peaks have been observed in 129Xe spectra from the human head in vivo.