title: Dynamics of magnetization in hyperpolarized gas MRI of the lung.
abstract: The magnetization in hyperpolarized gas (HP) MRI is generated by laser polarization that is independent of the magnet and imaging process. As a consequence, there is no equilibrium magnetization during the image acquisition. The competing processes of gas inflow and depolarization of the spins lead to large changes in signal as one samples k-space. A model is developed of dynamic changes in polarization of hyperpolarized 3He during infusion and in vivo imaging of the lung and verified experimentally in a live guinea pig. Projection encoding is used to measure the view-to-view variation with temporal resolution < 4 ms. Large excitation angles effectively sample the magnetization in the early stages of inflow, highlighting larger airways, while smaller excitation angles produce images of the more distal spaces. The work provides a basis for pulse sequences designed to effectively exploit HP MRI in the lung.
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: G A
authors.initials: GA
authors.lastname: Johnson
authors.forename: G
authors.initials: G
authors.lastname: Cates
authors.forename: X J
authors.initials: XJ
authors.lastname: Chen
authors.forename: G P
authors.initials: GP
authors.lastname: Cofer
authors.forename: B
authors.initials: B
authors.lastname: Driehuys
authors.forename: W
authors.initials: W
authors.lastname: Happer
authors.forename: L W
authors.initials: LW
authors.lastname: Hedlund
authors.forename: B
authors.initials: B
authors.lastname: Saam
authors.forename: M D
authors.initials: MD
authors.lastname: Shattuck
authors.forename: J
authors.initials: J
authors.lastname: Swartz
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D006371:Helium; D007554:Isotopes; D008168:Lung / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012119:Respiration
chemical_list: D007554:Isotopes; D006371:Helium