title: Effects of Frequency Drift on the Quantification of Gamma-Aminobutyric Acid Using MEGA-PRESS.
abstract: The MEGA-PRESS method is the most common method used to measure γ-aminobutyric acid (GABA) in the brain at 3T. It has been shown that the underestimation of the GABA signal due to B0 drift up to 1.22 Hz/min can be reduced by post-frequency alignment. In this study, we show that the underestimation of GABA can still occur even with post frequency alignment when the B0 drift is up to 3.93 Hz/min. The underestimation can be reduced by applying a frequency shift threshold. A total of 23 subjects were scanned twice to assess the short-term reproducibility, and 14 of them were scanned again after 2-8 weeks to evaluate the long-term reproducibility. A linear regression analysis of the quantified GABA versus the frequency shift showed a negative correlation (P < 0.01). Underestimation of the GABA signal was found. When a frequency shift threshold of 0.125 ppm (15.5 Hz or 1.79 Hz/min) was applied, the linear regression showed no statistically significant difference (P > 0.05). Therefore, a frequency shift threshold at 0.125 ppm (15.5 Hz) can be used to reduce underestimation during GABA quantification. For data with a B0 drift up to 3.93 Hz/min, the coefficients of variance of short-term and long-term reproducibility for the GABA quantification were less than 10% when the frequency threshold was applied.
authors.affiliation: Graduate Institute of Applied Physics, National Chengchi University, Taipei, Taiwan.|Research Center for Mind, Brain and Learning, National Chengchi University, Taipei, Taiwan.
authors.forename: Shang-Yueh
authors.initials: SY
authors.lastname: Tsai
authors.affiliation: Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
authors.forename: Chun-Hao
authors.initials: CH
authors.lastname: Fang
authors.affiliation: Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
authors.forename: Thai-Yu
authors.initials: TY
authors.lastname: Wu
authors.affiliation: Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
authors.forename: Yi-Ru
authors.initials: YR
authors.lastname: Lin
mesh_terms: D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism*; D006801:Humans; D008279:Magnetic Resonance Imaging; D015203:Reproducibility of Results; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005680:gamma-Aminobutyric Acid