Mapping amide protons in the human brain at 3 and 7 Tesla using downfield MRSI

Motivation: Downfield magnetic resonance spectroscopic imaging (DF-MRSI) at high magnetic field strengths is expected to have superior signal-to-noise ratios (SNR) and spectral resolution compared to lower field. However, to date there have been no studies systematically comparing DF-MRSI across different field strengths. Goal(s): To quantitatively compare SNR, linewidths, and Cramér-Rao Lower Bounds (CRLB) for amide resonances in the human brain measured at 3 and 7T using (DF-MRSI). Approach: Seven healthy volunteers were scanned at 3T and 7T using closely-matched DF-MRSI protocols. Results: DF-MRSI at 7T showed 86% increased SNR and 57% decreased CRLB values compared to 3T. Water linewidths were narrower at 3T. Impact: Amide mapping using DF-MRSI at 7T showed significantly superior precision compared to 3T, and therefore is the preferred field strength for future research studies of DF metabolites.