Dynamic MR Spectroscopy of brain metabolism using a non-conventional spectral averaging scheme

MRS acquisition based on the blood oxygenation level dependent (BOLD) contrast mechanism was implemented at 3T to investigate the impact of a non-conventional spectral averaging scheme (determined by the number of RF excitations, NEX) on the dynamics of cerebral metabolism during neuroactivation. Using NEX=2, water and metabolite BOLD responses were compared to previous results from standard experiments.

Spectra were recorded from the visual cortex of five healthy volunteers during single and block visual stimulations. The height, width and area of the spectral peaks were calculated (using SAGE v7) in order to estimate their percentage changes from baseline (representing the BOLD change) following visual stimulation. BOLD changes were statistically significant at a significance level of p<0.05 by paired t-test.

Significantly greater BOLD changes in all spectra were observed in the single than block stimulation (p<0.05). The water resonance showed significant (p<0.01) BOLD changes in all peak parameters in both paradigms. All metabolites showed significant increase in spectral height (p<0.01) in the single paradigm, but none of them (except the height of Cho) showed significant BOLD response in the block paradigm. BOLD changes observed in the block paradigm were generally lower than reported changes.

The time interval of 6s offered by NEX=2 during which each line of spectral data is recorded by the scanner is rather long, leading to some BOLD data loss particularly in a block experimental design.