Hyperpolarized ¹²⁹Xe Phase-selective Imaging of Mouse Lung at 9.4T Using a Continuous-flow Hyperpolarizing System

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The use of hyperpolarized (HP) ¹²⁹Xe magnetic resonance (MR) imaging to regionally evaluate gas diffusion and perfusion processes as well as ventilation in the lung has been expected. In this study, we used a continuous-flow hyperpolarizing (CF-HP) system to acquire gas- and dissolved-phase ¹²⁹Xe images from mouse lung, employing standard gradient echo sequence equipped with chemical shift selective excitation and 90° flip angle. The character of non-recoverable HP magnetization enabled the use of a phase (frequency)-selective 90° pulse for direct visualization of only a given-phase ¹²⁹Xe magnetization replenished into the slice during repetition time (TR). We combined gas- and dissolved-phase ¹²⁹Xe images to map the ratio of dissolved- to gas-phase ¹²⁹Xe replenished into the slice during TR (M_dissolved/M_gas) and found it to be approximately 0.05 to 0.08 in the peripheral regions of mouse lungs. This result suggested that replenishment of dissolved-phase ¹²⁹Xe magnetization by gas diffusion and pulmonary perfusion would be faster than that of gas-phase by ventilation. The use of a CF-HP system that allows the application of relatively long TR to HP ¹²⁹Xe imaging using a phase-selective 90° pulse would be useful in evaluating gas transport mechanisms in the lung.