title: A novel selective-excitation RF pulse for magnetic resonance imaging.
abstract: OBJECTIVE
  A selective-excitation radiofrequency (RF) pulse that uses hard pulses composed of a sequence of composite pulses with positive and negative phases (P/N pulse) is proposed herein. Because the amplitude of the RF signal is unchanged during the excitation, RF amplification can be accomplished using a nonlinear RF power amplifier (i.e., class C or D type).
  
  
  METHODS
  In this article, Fourier series have been first used to analyze the equivalence between the proposed P/N pulse and the conventional soft pulse on selective excitation. Subsequently, computer simulations based on density-matrix theory are used to compare the excitation profiles of both the soft and the P/N pulses.
  
  
  RESULTS
  The excitation profiles of the P/N pulses have been measured experimentally through a home-built 0.3-T magnetic resonance imaging (MRI) system. In addition, several slices of images have been obtained as proofs by using the multislice two-dimensional spin echo sequence through replacement of the conventional soft pulse by the proposed P/N pulse.
  
  
  CONCLUSIONS
  Because the perfect selectivity of the proposed P/N pulse, it can be used for imaging studies to improve the efficiency of amplification at the lowest cost.
authors.affiliation: Shanghai Key Laboratory of Functional Magnetic Resonance Imaging, Department of Physics, East China Normal University, Shanghai 200062, People's Republic of China. ling2431@163.com
authors.forename: Liu
authors.initials: L
authors.lastname: Ying
authors.forename: Li
authors.initials: L
authors.lastname: Jianqi
authors.forename: Li
authors.initials: L
authors.lastname: Gengying
mesh_terms: D001921:Brain / Q000033:anatomy & histology*; D003198:Computer Simulation; D005583:Fourier Analysis; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods