title: Improved encoding pulses for Bloch-Siegert B1(+) mapping.
abstract: A new family of optimized encoding pulses for Bloch-Siegert (BS) |B(1)(+)| mapping is introduced, as well as an algorithm to design them. The pulses are designed by numerical maximization of BS sequence sensitivity, subject to constraints that ensure low on-resonance excitation. The pulses are in all cases characterized by a constant envelope and U-shaped frequency sweep. They are validated in simulations, 7T in vivo experiments, and an experiment to measure their on-resonance excitation, and are compared to a Fermi pulse conventionally used in the BS method. The pulses are shown to produce larger phase shifts in a shorter time and with lower on-resonance excitation than the Fermi pulse, which results in lower SAR and improved |B(1)(+)| accuracy in areas of the body with large main field inhomogeneities.
authors.affiliation: Vanderbilt University Institute of Imaging Science, Nashville, TN 37232-2310, USA. m.jankiewicz@vanderbilt.edu
authors.forename: Marcin
authors.initials: M
authors.lastname: Jankiewicz
authors.forename: John C
authors.initials: JC
authors.lastname: Gore
authors.forename: William A
authors.initials: WA
authors.lastname: Grissom
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000706:statistics & numerical data*; D019047:Phantoms, Imaging; D015203:Reproducibility of Results