MEGA-PRESS of GABA+: Influences of acquisition parameters

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γ-aminobutyric acid (GABA) was the first molecule that was edited with MEGA-PRESS. GABA edited spectroscopy is challenged by limited selectivity of editing pulses. Coediting of resonances from macromolecules (MM) is the greatest single limitation of GABA edited spectroscopy. In this contribution, relative signal contributions from GABA, MM and homocarnosine to the total MEGA-PRESS edited signal at ~3 ppm, i.e., GABA+, are simulated at 3 tesla using several acquisition schemes. The base scheme is modeled after those currently supplied by vendors: it uses typical pulse shapes and lengths, it minimizes the first echo time (TE), and the delay between the editing pulses is kept at TE/2. Edited spectra are simulated for imperfect acquisition parameters such as incorrect frequency, larger chemical shift displacement, incorrect transmit B1-field calibration for localization and editing pulses, and longer TE. An alternative timing scheme and longer editing pulses are also considered. Additional simulations are performed for symmetric editing around the MM frequency to suppress the MM signal. The relative influences of these acquisition parameters on the constituents of GABA+ are examined from the perspective of modern experimental designs for investigating brain GABA concentration differences in healthy and diseased humans. Other factors that influence signal contributions, such as T1 and T2 relaxation times are also considered.

Original languageEnglish (US)
Article numbere4199
JournalNMR in biomedicine
Issue number5
Early online dateOct 28 2019
StatePublished - Oct 28 2019

Bibliographical note

Funding Information:
This work was supported by the National Institutes of Health grant number P41 EB015894 and P30 NS076408. We thank Robin de Graaf for providing the Lys coupling system.

Publisher Copyright:
© 2019 John Wiley & Sons, Ltd.


  • GABA
  • editing
  • homocarnosine
  • lysine
  • macromolecules
  • magnetic resonance spectroscopy


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