title: Self-refocused adiabatic pulse for spin echo imaging at 7 T.
abstract: Spin echo pulse sequences are used to produce clinically important T(2) contrast. However, conventional 180° radiofrequency pulses required to generate a spin echo are highly susceptible to the B(1) inhomogeneity at high magnetic fields such as 7 Tesla (7 T), resulting in varying signal and contrast over the region of interest. Adiabatic 180° pulses may be used to replace conventional 180° pulses in spin echo sequences to provide greater immunity to the inhomogeneous B(1) field at 7 T. However, because the spectral profile of an adiabatic 180° pulse has nonlinear phase, pairs of these pulses are needed for proper refocusing, resulting in increased radiofrequency power deposition and long minimum echo times. We used the adiabatic Shinnar Le-Roux method to generate a matched-phase adiabatic 90°-180° pulse pair to obviate the need for a second adiabatic 180° pulse for phase refocusing. The pulse pair was then reformulated into a single self-refocused pulse to minimize the echo time, and phantom and in vivo experiments were performed to validate pulse performance. The self-refocused adiabatic pulse produced transmit profiles that were substantially more uniform than those achieved using a conventional spin echo sequence.
authors.affiliation: Department of Radiology, Stanford University, Stanford, CA, USA. pritib@stanford.edu
authors.forename: Priti
authors.initials: P
authors.lastname: Balchandani
authors.forename: Mohammad Mehdi
authors.initials: MM
authors.lastname: Khalighi
authors.forename: Gary
authors.initials: G
authors.lastname: Glover
authors.forename: John
authors.initials: J
authors.lastname: Pauly
authors.forename: Daniel
authors.initials: D
authors.lastname: Spielman
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging; D013113:Spin Labels
chemical_list: D013113:Spin Labels