Functional ³¹P Magnetic Resonance Spectroscopy at 9.4 T

Area of Science:

• Neuroimaging
• Metabolic Neuroscience
• Magnetic Resonance Spectroscopy

Background:

• ³¹P MRS offers insights into brain energy metabolism during stimulation.
• Detecting subtle spectral changes is hindered by low signal-to-noise ratio (SNR) and large voxel sizes.
• Higher field strengths and advanced receiver arrays can improve detection of brain activation metabolism.

Purpose of the Study:

• To investigate functional ³¹P MRS during visual stimulation at 9.4T.
• To assess the detectability of brain energy metabolism changes using a 27-element array and 3D-CSI.
• To evaluate the impact of postprocessing algorithms on subtle spectral change detection.

Main Methods:

• Acquired functional ³¹P MRS data at 9.4T with a 27-element array and 3D-CSI.
• Measured T₁ values at 9.4T.
• Presented a 4.5-minute visual stimulus to healthy subjects during a 45-minute CSI acquisition.
• Averaged stimulus and rest epochs for spectral analysis.
• Applied spectral denoising and spatial deconvolution postprocessing techniques.

Main Results:

• Confirmed decreasing T₁ values with increasing field strength.
• Acquired high-quality spectra with good SNR.
• Observed a small but significant chemical shift difference in inorganic phosphate between stimulus and rest, potentially indicating a pH increase.
• Spectral denoising improved SNR but suppressed the chemical shift difference.
• Spatial deconvolution enhanced resolution but did not reveal additional changes.

Conclusions:

• Functional ³¹P MRS at 9.4T reveals only very subtle spectral changes during visual stimulation.
• These subtle changes are difficult to detect, even with high SNR and spectral dispersion.
• Current postprocessing methods do not sufficiently enhance the detection of these minute metabolic shifts.