Effects of pulmonary inhalation on hyperpolarized krypton-83 magnetic resonance T₁ relaxation

The ⁸³Kr magnetic resonance (MR) relaxation time T₁ of krypton gas in contact with model surfaces was previously found to be highly sensitive to surface composition, surface-to-volume ratio, and surface temperature. The work presented here explored aspects of pulmonary ⁸³Kr T₁ relaxation measurements in excised lungs from healthy rats using hyperpolarized (hp) ⁸³Kr with approximately 4.4% spin polarization. MR spectroscopy without spatial resolution was applied to the ex vivo lungs that actively inhale hp ⁸³Kr through a custom designed ventilation system. Various inhalation schemes were devised to study the influence of anatomical dead space upon the measured ⁸³Kr T ₁ relaxation times. The longitudinal ⁸³Kr relaxation times in the distal airways and the respiratory zones were independent of the lung inhalation volume, with T₁ = 1.3 s and T₁ = 1.0 s, depending only on the applied inhalation scheme. The obtained data were highly reproducible between different specimens. Further, the ⁸³Kr T ₁ relaxation times in excised lungs were unaffected by the presence of up to 40% oxygen in the hp gas mixture. The results support the possible importance of ⁸³Kr as a biomarker for evaluating lung function.