In vivo proton magnetic resonance spectroscopic imaging of the healthy human brain at 9.4 T: initial experience

In this study, the feasibility of in vivo proton magnetic resonance spectroscopic imaging (H-1 MRSI) of the healthy human brain at a field strength of 9.4 T, using conventional acquisition techniques, is examined and the initial experience is summarized. MRSI measurements were performed on a 9.4 T MR scanner (Siemens, Erlangen, Germany) equipped with head-only gradient insert (AC84, Siemens) and custom-developed, 8-channel transmit/24-channel receive, and 16-channel transmit/31-channel receive coils. Spectra were acquired from the superior part of the human brain with a modified STEAM sequence. Spectral quantification was done with LCModel software. Reasonable quality and signal-to-noise ratio of the acquired spectra allowed reliable quantification of 12 metabolites (Cramer-Rao lower bounds < 20 %), some of which may be difficult to quantify at field strengths below 7 T due to overlapping resonances or low concentrations. While further developments are necessary to minimize chemical shift displacement and homogeneity of the transmit field, it is demonstrated that in vivo H-1 MRSI at a field strength of 9.4 T is possible. However, further studies applying up-to-date techniques to overcome high-field specific problems are needed in order to assess the potential gain in sensitivity that may be offered by MRSI at 9.4 T.