Fast and efficient free induction decay MR spectroscopic imaging of the human brain at 9.4 Tesla.

PurposeThe purpose of this work was to develop a fast and efficient MRSI-FID acquisition scheme and test its performance in vivo. The aim was to find a trade-off between the minimal total acquisition time and signal-to-noise ratio of the acquired spectra. MethodsMeasurements were performed on a 9.4 Tesla system. Sequence optimization included redesign of water suppression, optimization of the sequence gradients, and improvement of the sampling efficiency by minimizing the read-out time. This resulted in an acquisition time of 2:47 and 22:13 minutes for 2D (TR=57 ms; 3-mm in-plane resolution) and 3D MRSI (TR=57 ms; 16 slices; 3-mm isotropic resolution), respectively. ResultsDespite strong T-1 weighting and first-order phase problems, it was possible to obtain spectra of an acceptable quality. The average line width calculated for the tCr peak across the entire field of view was 26.99.6Hz for 2D and 30.0 +/- 11.3Hz for 3D MRSI. In 3D measurements, the percent fraction of voxels fitted with Cramer-Rao lower bounds below 10% was 53.3 +/- 4.1%, 63.4 +/- 8.4%, and 81.0 +/- 2.9% for Glu, tCr, and tNAA, respectively. ConclusionConsidering the typically long duration of high-resolution MRSI, the proposed technique may be of interest for clinical applications and/or studies that focus on following the biochemistry of dynamic processes. Magn Reson Med 78:1281-1295, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.