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 mm3. 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 echo-volumar 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 mm3) 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.
Bibliographical noteFunding Information:
This research was in part supported by NIH grants 1R21EB011606–01, 1 R01 DA14178–01, R01 HD065283, P41 EB015894 and P41 EB027061.
This research was in part supported by 1R21EB011606‐01, 1 R01 DA14178‐01, R01 HD065283, P41 EB015894 and P41 EB027061. We gratefully acknowledge our former lab members, Elena Ackley and Chenguang Zhao, for developing spectral reconstruction in ICE, upon which this methodology is built. We thank our neurosurgeons, Muhammad Omar Chohan and Howard Yonas, for their support in studying the patients with brain tumors. Akram Etemadi Amin, Mona Chaney, Neva M. Corrigan, Lakshmisree Damodaran, Mindy Dixon, Dennis Shaw and Diana South provided technical support, assistance with scans and support with patient recruitment.
© 2020 John Wiley & Sons, Ltd.
- functional MRI acquisition techniques (BOLD and non-BOLD)
- multimodality imaging
- quantitative MRS
- resting-state functional MRI
- sampling strategies
- spectroscopic imaging
- water referencing