Analysis of short-TE STEAM data at 7T: Effects of a macromolecular basis set and baseline parameters on GABA, glutamate and their ratio.

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The effect of baseline flexibility LCModel parameter DKNTMN (0.15, 0.3, 0.6 and 1) on a 7T short-TE STEAM MRS measurement of GABA, glutamate and excitatory-inhibitory ratio (EIR) was investigated using both simulated and measured macromolecular basis sets. Mean (SD) of GABA/tCr was highest, 0.23 (0.02), using simulated MM basis. Using measured MM basis, the ratios decreased from 0.18 (0.04) to 0.12 (0.03) by the increase of DKNTMN values. The GABA/tCr ratio and EIR of a former multi-center study was 0.19 and 8.2 after T2 decay correction. Analysis using DKNTMN of 0.3 conformed best and considered to be the choice.