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 He-3 in human lung. A quantitative treatment of signal attenuation and magnetization consumption for the unique circumstance of a rapidly diffusin g nonrenewable magnetization source has been performed. Rapid (compared to the human respiratory cycle) and repetitive imaging of the lung gas space w ith EPI and a single delivered bolus of HP-He-3 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 hea lthy volunteers during rebreathing of a HP-He-3/N-2 gas mixture. A set of t hree 10-mm axial slices was imaged every 0.12 sec for the 36 sec duration o f rebreathing, yielding a real-time visualization of ventilation. Despite s ome mild artifacts, the images are of good quality and show changes in gas density related to respiratory physiology, (C) 1999 Wiley Liss,Inc.