Short Echo-Time Spiral MRSI Versus Single-Voxel Spectroscopy in the Human Brain at 3 Tesla With Semi-LASER...

Magnetic resonance spectroscopy techniques are widely used to non-invasively study brain metabolism. Despite advances in magnetic resonance spectroscopic imaging (MRSI), there is a notable absence of research on comparing fast non-Cartesian MRSI with single-voxel spectroscopy (SVS), limiting our understanding of its performance and applicability. In this study, we compared the spectral quality and metabolite concentrations obtained using short-T_E 2D spiral MRSI and SVS in the same region in the human brain at 3T.

Five healthy subjects were scanned at 3T. 2D spiral MRSI data were acquired in a transverse slice through the posterior cingulate cortex (PCC), while the SVS volume was placed within the PCC region. Both techniques employed the standardized semi-LASER sequence for localization. All data were processed in Matlab and fitted with LCModel.

Visual inspection suggested comparable overall spectral quality between the two acquisitions. Quantitatively, however, the PCC voxel measured with MRSI exhibited lower signal-to-noise ratio (SNR) compared to SVS at identical scan times, when the SVS voxel matched the effective MRSI voxel. Consistent with lower SNR, metabolite quantification showed higher Cramer-Rao lower bounds with MRSI. In addition, concentrations of glutamate and glutamate plus glutamine were lower with MRSI.

Our findings demonstrate that the quality of semi-LASER localized short-TE spiral MRSI spectra is very comparable to that of semi-LASER localized SVS spectra. Small metabolic-specific concentration differences may be due to different WM/GM tissue weighting within the voxel (slice selection profile in SVS vs. point-spread function in MRSI) and different SNR between the two techniques.