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

We present a new method to determine in vivo the temporal evolution of intrapulmonary oxygen concentrations by functional lung imaging with hyperpolarized (3)Helium ((3)>(He)over right arrow>). Single-breath, single-bolus visualization of 3<(He)over right arrow>administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial pressure p(O2)(t). We model the dynamics of hyperpolarization in the lung by rate equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It permits the determination of p(O2) with a high accuracy of up to 3% with simultaneous flip angle calibration using no additional input parameters. The time course of P-O2 during short periods of breathholding is found to be linear in a pig as well as in a human volunteer. We also measured the wall relaxation time in the lung and deduced a lower limit of 4.3 min. (C) 1999 Academic Press.