FUNCTIONAL PROTON MAGNETIC RESONANCE SPECTROSCOPY OF CEREBRAL WATER AND METABOLITES USING EIGHT RADIOFREQUENCY EXCITATIONS AT 3.0 TESLA

Abstract

MRS acquisition focusing on the blood oxygenation level dependent (BOLD) contrast mechanism was implemented in this study to investigate the impact of spectral averaging (determined by the number of RF excitations, NEX) on the dynamics of cerebral metabolism during neuroactivation. Materials and Methods: Using NEX = 8, the BOLD effects on cerebral water and six metabolites were studied at 3.0 T. Spectra were recorded from the visual cortex of four healthy volunteers during single and interleaved visual stimulations. Results: Generally, single stimulation was found to induce greater BOLD effects on the water and metabolite resonances than interleaved stimulation (p = 0.02). The water resonance showed significant (p < 0.01) increase in peak height (18.4%) and decrease in linewidth (-3.5%) in the single, but not in the interleaved stimulation. The water peak area however did not change significantly in both stimulation paradigms. Only Cr showed significant linewidth decrease (-3.1%) in the interleaved stimulation paradigm (p = 0.04). In the single stimulation paradigm, both NAA (11.2%; p = 0.01) and Cr (7.2%; p = 0.02) showed significant increases in their peak areas, while Cho was the only metabolite that showed significant increase in its peak height (2.2%; p = 0.01). Glu, Gln, and mI did not show significant BOLD responses in both paradigms (p > 0.05). Conclusion: The results of this study were consistent with previous studies at higher fields, indicating that NEX = 8 could improve accuracy of functional MRS studies at lower fields and at the same time offer quicker spectral averaging