title: Impact of frequency drift on gamma-aminobutyric acid-edited MR spectroscopy.
abstract: OBJECTIVE
  To investigate the quantitative impact of frequency drift on Gamma-Aminobutyric acid (GABA+)-edited MRS of the human brain at 3 Tesla (T).
  
  
  METHODS
  Three sequential GABA+-edited MEGA-PRESS acquisitions were acquired in fifteen sessions; in ten of these, MRS was preceded by functional MRI (fMRI) to induce frequency drift, which was estimated from the creatine resonance at 3.0 ppm. Simulations were performed to examine the effects of frequency drift on the editing efficiency of GABA and co-edited macromolecules (MM) and of subtraction artifacts on GABA+ quantification. The efficacy of postprocessing frequency correction was also investigated.
  
  
  RESULTS
  Gradient-induced frequency drifts affect GABA+ quantification for at least 30 min after imaging. Average frequency drift was low in control sessions and as high as -2 Hz/min after fMRI. Uncorrected frequency drift has an approximately linear effect on GABA+ measurements with a -10 Hz drift resulting in a 16% decrease in GABA+, primarily due to subtraction artifacts.
  
  
  CONCLUSIONS
  Imaging acquisitions with high gradient duty cycles can impact subsequent GABA+ measurements. Postprocessing can address subtraction artifacts, but not changes in editing efficiency or GABA:MM signal ratios; therefore, protocol design should avoid intensive gradient sequences before edited MRS Magn Reson Med 72:941-948, 2014. © 2013 Wiley Periodicals, Inc.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University, Baltimore, Maryland, USA; F.M. Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA.
authors.forename: Ashley D
authors.initials: AD
authors.lastname: Harris
authors.forename: Benjamin
authors.initials: B
authors.lastname: Glaubitz
authors.forename: Jamie
authors.initials: J
authors.lastname: Near
authors.forename: C
authors.initials: C
authors.lastname: John Evans
authors.forename: Nicolaas A J
authors.initials: NA
authors.lastname: Puts
authors.forename: Tobias
authors.initials: T
authors.lastname: Schmidt-Wilcke
authors.forename: Martin
authors.initials: M
authors.lastname: Tegenthoff
authors.forename: Peter B
authors.initials: PB
authors.lastname: Barker
authors.forename: Richard A E
authors.initials: RA
authors.lastname: Edden
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000378:metabolism*; D005260:Female; D006801:Humans; D046911:Macromolecular Substances / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008297:Male; D018377:Neurotransmitter Agents / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D018377:Neurotransmitter Agents; D005680:gamma-Aminobutyric Acid
keywords: GABA; edited MRS; editing efficiency; frequency drift; subtraction artifact