title: Subtraction artifacts and frequency (mis-)alignment in J-difference GABA editing.
abstract: OBJECTIVE
  To compare the repeatability of γ-aminobutyric acid (GABA) measurements using J-difference editing, before and after spectral realignment-a technique which has previously been demonstrated to improve the quality of J-difference GABA spectra.
  
  
  METHODS
  We performed in vivo measurements in three brain regions (occipital, sensorimotor, and dorsolateral prefrontal cortex [DLPFC]), and analyzed these using alternative alignment approaches to evaluate the impact of alignment on repeatability: "Independent alignment" (aligning each subspectrum independently) and "Pairwise alignment" (aligning each on and off subspectrum as a pair) were compared.
  
  
  RESULTS
  Pairwise alignment improved the group mean coefficient of variation in all regions; 0.4% in occipital, 1.1% in sensorimotor, and 1.1% in DLPFC. Independent alignment resulted in subtraction artifacts in the majority of cases, and increased the coefficient of variation in the DLPFC by 9.4%. Simulations demonstrate that the GABA quantification error in datasets with high B0 drift, is 4.5% without alignment, but <1% with optimal alignment.
  
  
  CONCLUSIONS
  Pairwise alignment improves the repeatability of GABA spectroscopy data. However, independently aligning all on and off subspectra can lead to artifacts and worse repeatability when compared with nonaligned data.
authors.affiliation: CUBRIC, School of Psychology, Cardiff University, Park Place, Cardiff, United Kingdom.
authors.forename: C John
authors.initials: CJ
authors.lastname: Evans
authors.forename: Nicolaas A J
authors.initials: NA
authors.lastname: Puts
authors.forename: Siân E
authors.initials: SE
authors.lastname: Robson
authors.forename: Frederic
authors.initials: F
authors.lastname: Boy
authors.forename: David J
authors.initials: DJ
authors.lastname: McGonigle
authors.forename: Petroc
authors.initials: P
authors.lastname: Sumner
authors.forename: Krish D
authors.initials: KD
authors.lastname: Singh
authors.forename: Richard A E
authors.initials: RA
authors.lastname: Edden
mesh_terms: D000328:Adult; D016477:Artifacts; D001921:Brain / Q000473:pathology*; D003198:Computer Simulation; D005260:Female; D005625:Frontal Lobe / Q000473:pathology; D006801:Humans; D016018:Least-Squares Analysis; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008875:Middle Aged; D009038:Motion; D009044:Motor Cortex / Q000473:pathology; D009778:Occipital Lobe / Q000473:pathology; D015203:Reproducibility of Results; D013382:Subtraction Technique; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000737:chemistry*
chemical_list: D005680:gamma-Aminobutyric Acid