DYNAMICS OF MAGNETIZATION IN HYPERPOLARIZED GAS MRI OF THE LUNG

The magnetization in hyperpolarized gas (HP) MRI is generated by laser polarization that is independent of the magnet and imaging process. A s a consequence, there is no equilibrium magnetization during the imag e acquisition, The competing processes of gas inflow and depolarizatio n of the spins lead to large changes in signal as one samples k-space, A model is developed of dynamic changes in polarization of hyperpolar ized He-3 during infusion and in vivo imaging of the lung and verified experimentally in a live guinea pig, Projection encoding is used to m easure the view-to-view variation with temporal resolution <4 ms, Larg e excitation angles effectively sample the magnetization in the early stages of inflow, highlighting larger airways, while smaller excitatio n angles produce images of the more distal spaces, The work provides a basis for pulse sequences designed to effectively exploit HP MRI in t he lung.