NMR of hyperpolarized (129)Xe in the canine chest: spectral dynamics during a breath-hold

One of the major goals of hyperpolarized-gas MR imaging has been to obtain (129)Xe dissolved-phase images in humans. Since the dissolved-phase signal is much weaker than the gas-phase signal, highly optimized MR pulse sequences are required to obtain adequate images during a single breath-hold. In particular, a solid understanding of the temporal dynamics of xenon as it passes from the lung gas spaces into the parenchyma, the blood and other downstream compartments is absolutely essential. Spectroscopy experiments were performed in the canine chest to elucidate the behavior of xenon exchange in the lung. The experiments covered a time range from 1 ms to 9 s and therefore considerably extend the data currently available in the literature. It was found that the integrals of the dissolved-phase resonances approached plateau values within approximately 200 ms, and then increased again after approximately 1 s. This behavior suggests an early saturation of the parenchyma before xenon reaches downstream compartments. Mono-exponential recovery curves with time constants on the order of 100 ms were fit to the data. These results potentially provide information on several underlying physiological parameters of the lung, including the parenchymal and blood volumes as well as the diffusion properties of lung tissue.