Efficient γ-aminobutyric acid editing at 3T without macromolecule contamination: MEGA-SPECIAL.

One of the most commonly used methods for in vivo MRS detection of γ-aminobutyric acid (GABA) is the MEGA-point-resolved spectroscopy (MEGA-PRESS) technique. However, accurate quantification of GABA using MEGA-PRESS is complicated by spectral co-editing of macromolecular resonances. In this article, a new pulse sequence is presented which enables GABA editing at 3T with the removal of macromolecule contamination. This sequence combines the conventional MEGA editing scheme with the SPECIAL localisation technique, and is therefore named MEGA-SPECIAL. Simulations and phantom experiments indicate that this new approach provides improved GABA editing efficiency relative to MEGA-PRESS, and in vivo results demonstrate effective removal of macromolecule contamination. In a study of the occipital lobe of five healthy volunteers, the macromolecule-corrected GABA/creatine ratio was found to be 0.093 ± 0.007 (mean ± standard deviation), whereas prior to macromolecule correction, the ratio was found to be 0.173 ± 0.013.