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High Resolution 3 He Pulmonary MRI

Hyperpolarized gas MRI of the mouse lung is of great interest due to the urgent need for novel biomarkers for the assessment of respiratory-disease progression and development of new therapies. Small animal 3 He lung MRI requires high-spatial-resolution imaging ( < 500 μ m) to obtain acceptable images for visualization of all branches of lung microstructure from the mouse trachea to lung parenchyma. The use of conventional fast-gradient-recalled echo (FGRE) pulse sequences for high-spatial-resolution mouse lung imaging is challenging due to the signal loss caused by significant diffusion-weighting by the imaging gradients, particularly in larger airways where 3 He diffusion is maximized. In this chapter, a modified FGRE approach called X-Centric is described for acquiring 3 He mouse lung MRI. X-Centric is a center-out technique, allowing high-spatial-resolution, and high signal-to-noise ratio density-weighted imaging, as it is a short-TE method minimizing diffusion decay. Here, we also take advantage of a high-performance insertable-gradient-set interfaced with a clinical MRI system and a custom-built constant-volume ventilator to get the maximum benefits of X-Centric. High-spatial-resolution 3 He X-Centric imaging was performed in a phantom and mouse lungs, yielding a nominal resolution of 39 μ m and 78 μ m respectively. We also demonstrate the feasibility of 129 Xe/ 19 F X-Centric MRI in a phantom and in rat lungs.