Measurement of 129Xe T1 in blood to explore the feasibility of hyperpolarized 129Xe MRI

Abstract

Objective: The major obstacle to the use of 129-xenon (I = 1/2) as a new source of contrast in magnetic resonance is its low sensitivity. The hyperpolarized 129Xe-MRI technique using laser optical pumping of rubidium promises to resolve this problem. The potential of xenon-based MRI for the body tissues other than the lung air spaces depends on the 129Xe polarization lifetime (T1) in the blood at a magnetic field of commonly available clinical MRI systems.

Materials and methods: Xenon with natural abundance of 129Xe (26%) was dissolved in human blood and studied at 36 degrees C in a 2.35 T 40 cm bore MRI spectrometer (27.6 MHz). Zeeman relaxation (T1) of six blood samples was measured by the progressive saturation method for periods of 4-8 h each.

Results: NMR spectra revealed two peaks at 216.0 ppm (A) and 194.0 ppm (B) relative to the xenon gas above the blood volume. Assignment and 129Xe T1 values were 4.5 +/- 1 s for red blood cells (A), 9.6 +/- 2 s for plasma (B) and 11.9 +/- 1.6 s for xenon gas at atmospheric oxygen pressure. Xenon dissolved in distilled water appears at 189.8 ppm and has T1 = 26.3 +/- 1.4 s.

Conclusion: These relaxation times, though shorter than expected, are comparable to the transport time of blood, and are long enough to encourage use of hyperpolarized xenon for MRI studies in tissues, in addition to lung.