SIGNAL DYNAMICS IN MAGNETIC-RESONANCE-IMAGING OF THE LUNG WITH HYPERPOLARIZED NOBLE-GASES

The nonequilibrium bulk magnetic moment of hyperpolarized (HP) noble g ases generated by optical pumping has unique characteristics. Based on the Bloch equations, a model was developed describing the signal dyna mics of HP gases used in magnetic resonance imaging (MRI) of the lung with special consideration to the breathing cycle. Experimental verifi cation included extensive investigations with HP He-3 and Xe-129 durin g both inspiration and held breath in live guinea pigs, Radial acquisi tion was used to investigate the view variations with a temporal resol ution of 5 ms. Agreement between theoretical predictions and in vivo r esults was excellent. Additionally, information about effects from nob le gas diffusion and spin-lattice relaxation was obtained. In vivo res ults for T-1 were 28.8 +/- 1.8 s for He-3 and 31.3 +/- 1.8 s for Xe-12 9. Comparison with in vitro data indicated that relaxation in the pulm onary gas space is dominated by dipolar coupling with molecular oxygen . The results provide a quantitative basis for optimizing pulse sequen ce design in HP gas MRI of the lung. (C) 1998 Academic Press.