Signal-to-noise ratio and spectral linewidth improvements between 1.5 and 7 tesla in proton echo-planar spectroscopic imaging

This study characterizes gains in sensitivity and spectral resolution of proton echo-planar spectroscopic imaging (PEPSI) with increasing magnetic field strength (B₀). Signal-to-noise ratio (SNR) per unit volume and unit time, and intrinsic linewidth (LW) of N-acetyl-aspartate (NAA), creatine (Cr), and choline (Cho) were measured with PEPSI at 1.5, 3, 4, and 7 Tesla on scanners that shared a similar software and hardware platform, using circularly polarized (CP) and eight-channel phased-array (PA) head coils. Data were corrected for relaxation effects and processed with a time-domain matched filter (MF) adapted to each B₀. The SNR and LW measured with PEPSI were very similar to those measured with conventional point-resolved spectroscopy (PRESS) SI. Measurements with the CP coil demonstrated a nearly linear SNR gain with respect to B₀ in central brain regions. For the PA coil, the SNR-B₀ relationship was less than linear, but there was a substantial SNR increase in comparison to the CP coil. The LW in units of ppm decreased with B₀, resulting in improved spectral resolution. These studies using PEPSI demonstrated linear gains in SNR with respect to B₀, consistent with theoretical expectations, and a decrease in ppm LW with increasing B₀.