GABA Fitting for MEGA-PRESS Sequences with Different Selective Inversion Frequencies

Introduction GABA detection faces the problem of contamination from co-edited macromolecule signal at 3.0 ppm (MM30) when using the MEGA-PRESS technique [1]. Therefore, direct quantification of GABA by LCModel software [2] yields the sum of GABA and MM30. One of the proposed methods to eliminate MM30 is to alternate the editing pulse between 1.9 ppm and 1.5 ppm, the latter a position symmetric to 1.9 ppm with respect to the J-coupled MM resonance at 1.7 ppm [3]. New MM basis have also been introduced into LCModel analysis [4], and a soft constraint has been applied to better quantify GABA [5]. In this study, we compare three LCModel fitting approaches for both the original MEGA-PRESS and the modified “MM-symmetric” sequence which has the editing pulse alternating between 1.9 ppm and 1.5 ppm.