Measurement and modeling of xenon gas transfer in the human brain with 1H and hyperpolarized 129Xe MRI

Background

The feasibility of imaging hyperpolarized ¹²⁹Xe dissolved in brain tissue following inhalation of xenon gas in the lungs has recently been demonstrated in humans. The image contrast in ¹²⁹Xe brain MRI represents a combination of factors, including regional perfusion, polarization decay and gas transfer rate across the blood-brain barrier.

Purpose

To investigate the repeatability of hyperpolarized ¹²⁹Xe brain MRI in healthy normal individuals and to identify the dominant mechanisms of image contrast by assessing voxel-wise correlation between HP ¹²⁹Xe brain MRI and models of ¹²⁹Xe brain uptake derived from ¹H arterial spin labeling (ASL) perfusion mapping.

Materials and Methods

To assess repeatability, 3 sets of hyperpolarized ¹²⁹Xe brain images were acquired from 5 healthy volunteers. Quantitative maps of the human brain, including cerebral blood flow, volume and predicted xenon uptake, were derived from ¹H arterial spin labeling and T₂-weighted MRI. These maps were then spatially cross-correlated with hyperpolarized ¹²⁹Xe brain MRI.

Results

Signal to noise ratios of 8.7–17.7 were observed across volunteers for a voxel size of 8 × 8 × 50 mm³ with intra-subject repeatability of between 6 and 29 %. Hyperpolarized ¹²⁹Xe brain images showed voxel-wise correlations with cerebral blood flow (R = 0.32 to 0.62), volume (R = 0.33 to 0.63) and predicted xenon uptake (R = 0.34 to 0.63), but did not correlate with arterial transit time (R = 0.05 to 0.26).

Conclusion

Voxel-wise cross correlation between ¹²⁹Xe and ¹H ASL suggests that the regional quantity of dissolved xenon delivered by cerebral blood flow is the dominant mechanism of image contrast in HP ¹²⁹Xe brain MRI, assuming normal blood-brain barrier function. Combining ¹H and ¹²⁹Xe brain MRI provides new opportunities to quantitatively investigate brain pathophysiology and function.