On the acquisition of the water signal during water suppression: High‐speed MR spectroscopic imaging with water referencing and concurrent functional MRI

Abstract

This study evaluated the utility of concurrent water signal acquisition as part of the water suppression in MR spectroscopic imaging (MRSI), to allow simultaneous water referencing for metabolite quantification, and to concurrently acquire functional MRI (fMRI) data. We integrated a spatial-spectral binomial water excitation RF pulse and a short spatial-spectral echo-planar readout into the water suppression module of 2D and 3D proton-echo-planar-spectroscopic-imaging (PEPSI) with a voxel size as small as 4 x 4 x 6 mm 3 . Metabolite quantification in reference to tissue water was validated in healthy controls for different prelocalization methods (spin-echo, PRESS and semi-LASER) and the clinical feasibility of a 3-minute 3D semi-Laser PEPSI scan (TR/TE: 1250/32 ms) with water referencing in patients with brain tumors was demonstrated. Spectral quality, SNR, Cramer-Rao-lower-bounds and water suppression efficiency were comparable with conventional PEPSI. Metabolite concentration values in reference to tissue water, using custom LCModel-based spectral fitting with relaxation correction, were in the range of previous studies and independent of the prelocalization method used. Next, we added a phase-encoding undersampled echovolumar imaging (EVI) module during water suppression to concurrently acquire metabolite maps with water referencing and fMRI data during task execution and resting state in healthy controls. Integration of multimodal signal acquisition prolongated minimum TR by less than 50 ms on average. Visual and motor activation in concurrent fMRI/MRSI (TR: 1250-1500 ms, voxel size: 4 x 4 x 6 mm 3 ) was readily detectable in single-task blocks with percent signal change comparable with conventional fMRI. Resting-state connectivity in sensory and motor networks was detectable in 4 minutes. This hybrid water suppression approach for multimodal imaging has the potential to significantly reduce scan time and extend neuroscience research and clinical applications through concurrent quantitative MRSI and fMRI acquisitions.

Advanced methodology for in vivo magnetic resonance spectroscopy

“…They cover latest research results in terms of novel advanced MRS methodology or its application. The methodology addresses issues in standardization, 19 diffusion MRS, [20][21][22] and editing, [23][24][25] as well as novel acquisition 26,27 and processing [28][29][30] techniques, while the reported applications probe the feasibility of novel uses of advanced MRS methods. [31][32][33] In summary, we hope that this special issue will be of value for all users and developers of MRS techniques in research or clinical use of MRS, be it by aiding in understanding concepts, writing publications or developing and implementing advanced MRS methods.…”

“…They cover latest research results in terms of novel advanced MRS methodology or its application. The methodology addresses issues in standardization, 19 diffusion MRS, 20–22 and editing, 23–25 as well as novel acquisition 26,27 and processing 28–30 techniques, while the reported applications probe the feasibility of novel uses of advanced MRS methods 31–33 …”