Rapid imaging of hyperpolarized gas using EPI.

Rapid repetitive MRI of hyperpolarized (HP) gases using echo-planar imaging (EPI) has been theoretically investigated and experimentally demonstrated for (3)He in human lung. A quantitative treatment of signal attenuation and magnetization consumption for the unique circumstance of a rapidly diffusing nonrenewable magnetization source has been performed. Rapid (compared to the human respiratory cycle) and repetitive imaging of the lung gas space with EPI and a single delivered bolus of HP-(3)He is feasible using low flip angles, provided the voxels are not too small. A coarse-grid (32 x 64) EPI pulse sequence has been developed and implemented to image the lungs of healthy volunteers during rebreathing of a HP-(3)He/N(2) gas mixture. A set of three 10-mm axial slices was imaged every 0.12 sec for the 36 sec duration of rebreathing, yielding a real-time visualization of ventilation. Despite some mild artifacts, the images are of good quality and show changes in gas density related to respiratory physiology. Magn Reson Med 42:507-514, 1999. Copyright 1999 Wiley-Liss, Inc.