title: Storage of magnetization as singlet order by optimal control designed pulses.
abstract: OBJECTIVE
  The use of hyperpolarization to enhance the sensitivity of MRI has so far been limited by the decay of the polarization through T1 relaxation. Recently, methods have been proposed that extend the lifetime of the hyperpolarization by storing the spin order in slowly relaxing singlet states.
  
  
  METHODS
  With this aim, optimal control theory was applied to create pulses that for near-equivalent spins accomplish transfers in and out of the singlet state with maximum efficiency while ensuring robustness toward variations in the nuclear spin system Hamiltonian (chemical shift, J-couplings, B1 and B0 magnetic field inhomogeneity).
  
  
  RESULTS
  The pulses are designed to accomplish efficient transfer with low B1 amplitude, essential for applications on preclinical and clinical MR scanners.
  
  
  CONCLUSIONS
  It is demonstrated that significantly improved efficiency and robustness can be obtained within the limitations of typical MR scanner performance.
authors.affiliation: Danish Research Centre for Magnetic Resonance, Hvidovre Hospital, Hvidovre, Denmark; MR Research Centre, Aarhus University Hospital, Aarhus, Denmark; Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, Aarhus University, Aarhus, Denmark.
authors.forename: Christoffer
authors.initials: C
authors.lastname: Laustsen
authors.forename: Sean
authors.initials: S
authors.lastname: Bowen
authors.forename: Mads Sloth
authors.initials: MS
authors.lastname: Vinding
authors.forename: Niels Chr
authors.initials: NC
authors.lastname: Nielsen
authors.forename: Jan H
authors.initials: JH
authors.lastname: Ardenkjaer-Larsen
mesh_terms: D000465:Algorithms; D001704:Biopolymers / Q000032:analysis*; D005246:Feedback; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013113:Spin Labels
chemical_list: D001704:Biopolymers; D013113:Spin Labels