Probing lung physiology with xenon polarization transfer contrast (XTC)

One of the major goals of hyperpolarized-gas MRI has been to obtain Xe-129 dissolved-phase images in humans. So far, this goal has remained elusive, m ainly due to the low concentration of xenon that dissolves in tissue. A met hod is proposed and demonstrated in dogs that allows information about the dissolved phase to be obtained by imaging the gas phase following the appli cation of a series of RF pulses that selectively destroy the longitudinal m agnetization of xenon dissolved in the lung parenchyma. During the delay ti me between consecutive RF pulses, the depolarized xenon rapidly exchanges w ith the gas phase, thus lowering the gas polarization. It is demonstrated t hat the resulting contrast in the Xe-129 gas image provides information abo ut the local tissue density. It is further argued that minor pulse-sequence modifications may provide information about the alveolar surface area or l ung perfusion. (C) 2000 Wiley-Liss, Inc.