Spectral peak areas do not vary according to spectral averaging scheme used in functional MRS experiments at 3 T with interleaved visual stimulation

Brain response to visual stimulation can be probed quantitatively using functional magnetic resonance spectroscopy (fMRS), which relies on the blood oxygenation level dependent (BOLD) contrast mechanism. BOLD effect in fMRS is associated with changes in the areas, widths, and heights of the MR spectra. This study investigated the effect of spectral averaging scheme (NEX value) on BOLD changes in the spectra. Using a visual stimulus at 8 Hz in single and interleaved stimulation paradigms, the BOLD effects in spectra acquired from the occipital brain region of three healthy volunteers (mean age ± SD = 32.7 ± 3.5 years) were compared for two fMRS data sets acquired with two NEX values ("2"and "8") available on a 3 T MR scanner. BOLD signal changes were estimated as percentage changes in spectral areas, heights, and widths of six cerebral metabolites and water using the SAGE software package (version 7). There was a general trend of lower BOLD effects with NEX = 8 in both stimulation paradigms. In the single stimulation paradigm, NEX = 8 was associated with significantly lower N-acetyl aspartate (NAA) spectral height (p = 0.03), creatine (p = 0.04) and choline (p = 0.02) spectral widths, and NAA (p = 0.03), water (p < 0.01), and glutamate (p = 0.02) spectral areas. In the interleaved stimulation paradigm, NEX = 8 was associated with significantly lower glutamate spectral height (p = 0.02), water (p = 0.03), and glutamine (p = 0.03) spectral widths, but there was no significant difference in all spectral areas between the two NEX values. Even though the two NEX values offered some differences in observable BOLD effects, their spectral areas were not significantly different in the interleaved visual stimulation experiments.