Stability of single-subject estimation of glutamate and GABA dynamics in concurrent fMRI-fMRS at 7 T

Motivation: Measuring neurochemical dynamics, particularly the concentrations of GABA and glutamate, at the single-subject level remains challenging due to the low SNR when a small number of transients are used in the averaging window. Goal(s): To assess the impact of different averaging window sizes on the stability of GABA and glutamate concentration estimates during the time-course of a visual stimulation experiment. Approach: We analyzed the data using various averaging window sizes to evaluate their effect on concentration stability. Results: Detecting single-subject changes in Glutamate and GABA remains challenging, even with a window size of 16 representing the largest practical window size in our experiments. Impact: In single-subject fMRS, choosing averaging window sizes with sufficient SNR is important for reliable measurements of glutamate and GABA dynamics. Further technical development both on the analysis side (temporal fitting) and acquisition side (real-time frequency drift correction) should be explored.