Fig. 2.

Flowchart of the MEGA-PRESS MRS data processing procedure and representative results of each step. (a). Schematic picture of the MEGA-PRESS MRS data processing procedure. (b) The processed GABA-edited difference spectrum (EDIT-OFF − EDIT-ON = DIFF) is the key output of the GannetLoad module. This plot shows the spectrum before frequency and phase correction (above in green) and the spectrum after frequency and phase correction (below in blue). (c) The Cr signal over the duration of the acquisition. The y-axis represents the frequency in ppm of the Cr signal. The spectra at each time point are presented as a vertical stripe in the image (color-coded according to signal intensity), so the Cr signal appears as a ‘hot’ stripe running through the image. In the lower half (POST), the result of frequency and phase correction is shown. (d) Model fitting of GABA+ and Glx spectrum peaks, representing the GABA+ signal modeling (GannetFit output). The blue line represents the actual edited spectrum while the overlaid red line is the model of best fit (using a simple Gaussian model by default). The residual is represented by the black curve below the modeling plot. (e) The modeling of the signal against which GABA is quantified, using the same color scheme as in (d). In our experiment, the unsuppressed water data were incorporated, so that the main spectrum is the water signal; the Cr signal is shown in an inset. The water signal was modeled as a mixed Gaussian-Lorentzian and served as the reference for GABA quantification