Abstract
The nonequilibrium bulk magnetic moment of hyperpolarized (HP) noble gases generated by optical pumping has unique characteristics. Based on the Bloch equations, a model was developed describing the signal dynamics of HP gases used in magnetic resonance imaging (MRI) of the lung with special consideration to the breathing cycle. Experimental verification included extensive investigations with HP3He and129Xe during both inspiration and held breath in live guinea pigs. Radial acquisition was used to investigate the view variations with a temporal resolution of 5 ms. Agreement between theoretical predictions andin vivoresults was excellent. Additionally, information about effects from noble gas diffusion and spin–lattice relaxation was obtained.In vivoresults forT1were 28.8 ± 1.8 s for3He and 31.3 ± 1.8 s for129Xe. Comparison within vitrodata indicated that relaxation in the pulmonary gas space is dominated by dipolar coupling with molecular oxygen. The results provide a quantitative basis for optimizing pulse sequence design in HP gas MRI of the lung.
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