  Optical pumping of He-3 produces large (hyper) nuclear-spin polarizations
independent of the magnetic resonance imaging (MRI) field strength. This allows
lung MRI to be performed at reduced fields with many associated benefits, such
as lower tissue susceptibility gradients and decreased power absorption rates.
Here we present results of 2D imaging as well as accurate 1D gas diffusion
mapping of the human lung using He-3 at very low field (3 mT). Furthermore,
measurements of transverse relaxation in zero applied gradient are shown to
accurately track pulmonary oxygen partial pressure, opening the way for novel
imaging sequences.
