title: J-difference editing of gamma-aminobutyric acid (GABA): simulated and experimental multiplet patterns.
abstract: OBJECTIVE
  To investigate factors that influence the multiplet pattern observed in J-difference editing of gamma-aminobutyric acid (GABA).
  
  
  METHODS
  Density matrix simulations were applied to investigate the shape of the 3 ppm GABA multiplet as a function of the editing sequence's slice-selective refocusing pulse properties, in particular bandwidth, transition width, and flip angle. For comparison to the calculations, experimental measurements were also made at 3 T on a 10 mM GABA solution using the MEGA-PRESS sequence at various refocusing pulse flip angles.
  
  
  RESULTS
  Good agreement was found between experiments and simulations. The edited multiplet consists of two outer lines of slightly unequal intensity due to strong coupling, and a smaller central line, the result of the unequal J-couplings between the C4 and C3 protons. The size of the center peak increases with increasing slice-selective refocusing pulse transition width, and deviation of the flip angle from 180°.
  
  
  CONCLUSIONS
  The 3 ppm GABA multiplet pattern observed in the MEGA-PRESS experiment depends quite strongly on the properties of the slice-selective refocusing pulses used. Under some circumstance, the central peak can be quite large; this does not necessarily indicate inefficient editing, or a subtraction artifact, but should be recognized as a property of the pulse sequence itself.
authors.affiliation: Douglas Mental Health University Institute and Department of Psychiatry, McGill University, Montreal, Canada; FMRIB Centre, University of Oxford, Oxford, UK.
authors.forename: Jamie
authors.initials: J
authors.lastname: Near
authors.forename: C John
authors.initials: CJ
authors.lastname: Evans
authors.forename: Nicolaas A J
authors.initials: NA
authors.lastname: Puts
authors.forename: Peter B
authors.initials: PB
authors.lastname: Barker
authors.forename: Richard A E
authors.initials: RA
authors.lastname: Edden
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008956:Models, Chemical; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D005680:gamma-Aminobutyric Acid / Q000032:analysis*
chemical_list: D005680:gamma-Aminobutyric Acid