title: Noninvasive evaluation of the regional variations of GABA using magnetic resonance spectroscopy at 3 Tesla.
abstract: OBJECTIVE
  Rapid regional fluctuations in GABA may result in inhomogeneous concentrations throughout the brain parenchyma. The goal of this study is to provide further insight into the natural distribution of GABA throughout the brain and thus determine if a surrogate site may be used for spectroscopy when evaluating motor diseases, neurological disorders, or psychiatric dysfunction.
  
  
  METHODS
  In this prospective study, eight healthy volunteers underwent spectroscopic evaluation of the frontal lobe, occipital lobe, lateral temporal lobe, basal ganglia, and both hippocampi using a spin echo variant of a J-difference editing method. Knowledge of the relative peak intensities of the macromolecule peaks at 3ppm and 0.9ppm was used to correct the contribution of co-edited macromolecules to the GABA peak at 3ppm. The GABA values were internally referenced to NAA. Linear regression was used to normalize the effect of regional tissue-fraction variation on the GABA/NAA values. A one-way ANOVA was performed with Tukey's multiple comparison test to compare the normalized GABA/NAA values in each pair of locations.
  
  
  RESULTS
  After accounting for the macromolecule contribution to the GABA signal and correction for tissue fraction variation, the normalized GABA/NAA ratios differ significantly between the six brain locations (p<0.001). Pairwise comparisons of the corrected normalized GABA/NAA ratios show statistically significant variation between the frontal lobe and the basal ganglia, frontal and lateral temporal lobes, and frontal lobe and right hippocampus. Variations in the normalized GABA/NAA ratios trend toward significance between the frontal lobe and left hippocampus, occipital lobe and the frontal lobe, occipital lobe and basal ganglia, and occipital lobe and right hippocampus.
  
  
  CONCLUSIONS
  Our study suggests that GABA concentration is inhomogeneous throughout the parenchyma. Studies evaluating the role of GABA must carefully consider voxel placement when incorporating spectroscopy.
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA. Electronic address: cdurst@virginia.edu.
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Durst
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore.
authors.forename: Navin
authors.initials: N
authors.lastname: Michael
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Tustison
authors.affiliation: Department of Public Health Sciences, University of Virginia, Charlottesville, VA, USA.
authors.forename: James T
authors.initials: JT
authors.lastname: Patrie
authors.affiliation: Department of Diagnostic Radiology and Nuclear Medicine, University of Maryland, Baltimore, MD, USA.
authors.forename: Prashant
authors.initials: P
authors.lastname: Raghavan
authors.affiliation: Department of Radiology and Medical Imaging, University of Virginia, Charlottesville, VA, USA.
authors.forename: Max
authors.initials: M
authors.lastname: Wintermark
authors.affiliation: Singapore Institute for Clinical Sciences, Agency for Science, Technology and Research, Singapore; Laboratory of Molecular Imaging, Singapore Bioimaging Consortium, Agency for Science, Technology and Research, Singapore, Singapore; Clinical Imaging Research Centre, Agency for Science, Technology and Research, Singapore, NUS-A*STAR, Singapore.
authors.forename: S
authors.initials: S
authors.lastname: Sendhil Velan
mesh_terms: D000328:Adult; D001921:Brain / Q000378:metabolism*; D001931:Brain Mapping / Q000379:methods*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D011446:Prospective Studies; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005680:gamma-Aminobutyric Acid
keywords: GABA; MRS; Regional variation; Segmentation; Spectroscopy