Quantification of regional intrapulmonary oxygen partial pressure evolution during apnea by He-3 MRI

We present a new method to determine in vivo the temporal evolution of intr apulmonary oxygen concentrations by functional lung imaging with hyperpolar ized (3)Helium ((3)>(He)over right arrow>). Single-breath, single-bolus vis ualization of 3<(He)over right arrow>administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial press ure p(O2)(t). We model the dynamics of hyperpolarization in the lung by rat e equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It per mits the determination of p(O2) with a high accuracy of up to 3% with simul taneous flip angle calibration using no additional input parameters. The ti me course of P-O2 during short periods of breathholding is found to be line ar in a pig as well as in a human volunteer. We also measured the wall rela xation time in the lung and deduced a lower limit of 4.3 min. (C) 1999 Acad emic Press.