Metabolite‐cycled STEAM and semi‐LASER localization for MR spectroscopy of the human brain at 9.4T

Purpose Metabolite cycling (MC) is an MRS technique for the simultaneous acquisition of water and metabolite spectra that avoids chemical exchange saturation transfer effects and for which water may serve as a reference signal or contain additional information in functional or diffusion studies. Here, MC was developed for human investigations at ultrahigh field. Methods MC‐STEAM and MC‐semi‐LASER are introduced at 9.4T with an optimized inversion pulse and elaborate coil setup. Experimental and simulation results are given for the implementation of adiabatic inversion pulses for MC. The two techniques are compared, and the effect of frequency and phase correction based on the MC water spectra is evaluated. Finally, absolute quantification of metabolites is performed. Results The proposed coil configuration results in a maximum B1 + of 48 μΤ in a voxel within the occipital lobe. Frequency and phase correction of single acquisitions improve signal‐to‐noise ratio (SNR) and linewidth, leading to high‐resolution spectra. The improvement of SNR of N‐acetylaspartate (SNRNAA) for frequency aligned data, acquired with MC‐STEAM and MC‐semi‐LASER, are 37% and 30%, respectively (P