Hyperpolarized ¹²⁹Xe MR Imaging with Balanced Steady-state Free Precession in Spontaneously Breathing Mouse Lungs

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Purpose: We investigated the characteristics of hyperpolarized (HP) ¹²⁹Xe magnetic resonance (MR) imaging obtained from balanced steady-state free precession (SSFP) measurement of mouse lungs, especially under spontaneous breathing, and compared the results with those obtained using traditional spoiled gradient echo (SPGR) method, focusing on improved signal-to-noise ratio (SNR) and reduced total acquisition time.
Methods: We calculated magnetization response of the HP ¹²⁹Xe gas for the balanced SSFP sequence under spontaneous breathing to derive optimal conditions for the imaging experiment. We then placed an anesthetized mouse in the magnet (9.4T) supplied with oxygen gas and a mixture of HP ¹²⁹Xe gas supplied from a continuous-flow hyperpolarizing system. We obtained an axial plane image of the lung through balanced SSFP and SPGR sequences, changing the various magnetic resonance (MR) imaging parameters, and measured the SNR of these images.
Results: We demonstrated the clear dependence of image intensity on flip angle and number of shots. The SNR was higher in balanced SSFP than in SPGR and 2.3-fold higher compared at each maximum. In contrast, total acquisition time in balanced SSFP was shortened to about one-eighth that of SPGR using a one-shot acquisition mode.
Conclusion: In HP ¹²⁹Xe MR imaging of the lung of a spontaneously breathing mouse, balanced SSFP sequence with multi-shot and centric order acquisition provides higher SNR in a shorter acquisition time than SPGR.