MEGA improves spectroscopy by revealing spectral peaks of interest which would otherwise remain hidden. It also allows detection and relative quantification of J-coupled metabolites such as gamma-aminobutyric acid (GABA) by automatically removing the spectral overlap from other metabolites. (In conventional spectroscopy, removing spectral overlap is only possible with spectral editing.) Frequency-selective RF pulses are included to manipulate the evolution of J-coupled MR signals. In addition, subtraction of on- and off-resonance spectra is used for relative quantification of J-coupled metabolites.