Unedited in vivo detection and quantification of γ-aminobutyric acid in the occipital cortex using short-TE MRS at 3 T

• Published in: NMR in biomedicine Vol. 26; no. 11; pp. 1353 - 1362
• Main Authors: Near, Jamie, Andersson, Jesper, Maron, Eduard, Mekle, Ralf, Gruetter, Rolf, Cowen, Philip, Jezzard, Peter
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.11.2013
• Subjects: Computer Simulation; Creatinine - metabolism; Female; gamma-Aminobutyric Acid - metabolism; Humans; Lipids - analysis; Macromolecular Substances - analysis; Magnetic Resonance Spectroscopy; Male; Metabolome; MRS; Occipital Lobe - metabolism; Reproducibility of Results; short-TE; spectral editing; Spin Labels; spin-echo full-intensity acquired localised (SPECIAL); Time Factors; Young Adult; γ-aminobutyric acid (GABA); γ-aminobutyric acid (GABA); spectral editing; spin-echo full-intensity acquired localised (SPECIAL); short-TE; MRS
• ISSN: 0952-3480; 1099-1492; 1099-1492
• DOI: 10.1002/nbm.2960

Short‐TE MRS has been proposed recently as a method for the in vivo detection and quantification of γ‐aminobutyric acid (GABA) in the human brain at 3 T. In this study, we investigated the accuracy and reproducibility of short‐TE MRS measurements of GABA at 3 T using both simulations and experiments. LCModel analysis was performed on a large number of simulated spectra with known metabolite input concentrations. Simulated spectra were generated using a range of spectral linewidths and signal‐to‐noise ratios to investigate the effect of varying experimental conditions, and analyses were performed using two different baseline models to investigate the effect of an inaccurate baseline model on GABA quantification. The results of these analyses indicated that, under experimental conditions corresponding to those typically observed in the occipital cortex, GABA concentration estimates are reproducible (mean reproducibility error, <20%), even when an incorrect baseline model is used. However, simulations indicate that the accuracy of GABA concentration estimates depends strongly on the experimental conditions (linewidth and signal‐to‐noise ratio). In addition to simulations, in vivo GABA measurements were performed using both spectral editing and short‐TE MRS in the occipital cortex of 14 healthy volunteers. Short‐TE MRS measurements of GABA exhibited a significant positive correlation with edited GABA measurements (R = 0.58, p < 0.05), suggesting that short‐TE measurements of GABA correspond well with measurements made using spectral editing techniques. Finally, within‐session reproducibility was assessed in the same 14 subjects using four consecutive short‐TE GABA measurements in the occipital cortex. Across all subjects, the average coefficient of variation of these four GABA measurements was 8.7 ± 4.9%. This study demonstrates that, under some experimental conditions, short‐TE MRS can be employed for the reproducible detection of GABA at 3 T, but that the technique should be used with caution, as the results are dependent on the experimental conditions. Copyright © 2013 John Wiley & Sons, Ltd. In this study, short‐TE MRS was investigated as a means of detecting γ‐aminobutyric acid (GABA) in the occipital cortex at 3 T. The accuracy and reproducibility of short‐TE MRS were assessed through both Monte Carlo simulations and in vivo experiments. Results indicate that the reproducibility of short‐TE GABA measurements in the occipital cortex is comparable with that of gold‐standard spectral editing approaches, but that the accuracy is strongly dependent on the experimental conditions.