Fig 4.

Group average SNR and fit error percentages as a function of scan duration (cumulative signal averaging) for GABA+, Glx and GSH in the ACC (black squares) and thalamus (grey circles). The fitted lines represent the square-root (for SNR) or inverse square-root (for the fit error) expected relationships. SNR increases with the square root of the number of averages for all three metabolites (R² > 0.9 for GABA+ and Glx, R² > 0.7 for GSH). GABA+ and Glx fit errors decrease with the square root of the number of averages (R² > 0.9), with a weaker negative relationship for GSH (R² ~ 0.2).