Phase-encoded single-voxel magnetic resonance spectroscopy for suppressing outer volume signals at 7 Tesla

Abstract

BACKGROUND Due to imperfect slice profiles, unwanted signals from outside the selected voxel may significantly contaminate metabolite signals acquired using in vivo magnetic resonance spectroscopy (MRS). The use of outer volume suppression may exceed the SAR threshold, especially at high field. OBJECTIVE We propose using phase-encoding gradients after radiofrequency (RF) excitation to spatially encode unwanted signals originating from outside of the selected single voxel. METHODS Phase-encoding gradients were added to a standard single voxel point-resolved spectroscopy (PRESS) sequence which selects a 2 × 2 × 2 cm3 voxel. Subsequent spatial Fourier transform was used to encode outer volume signals. Phantom and in vivo experiments were performed using both phase-encoded PRESS and standard PRESS at 7 Tesla. Quantification was performed using fitting software developed in-house. RESULTS Both phantom and in vivo studies showed that spectra from the phase-encoded PRESS sequence were relatively immune from contamination by oil signals and have more accurate quantification results than spectra from standard PRESS spectra of the same voxel. CONCLUSION The proposed phase-encoded single-voxel PRESS method can significantly suppress outer volume signals that may appear in the spectra of standard PRESS without increasing RF power deposition.

Estimation and removal of spurious echo artifacts in single‐voxel MRS using sensitivity encoding

“…14 It has also been previously proposed to add phase-encoding gradients to single-voxel MRS acquisitions followed by spatial Fourier transformation, to separate the desired region-of-interest signal from out-of-voxel artifacts. [15][16][17] The separation of spectral components from anatomical regions using receive coil information has also been shown using the SPLASH technique. 18 In the current study, it was hypothesized that sensitivity information from multiple receive coils could be used to separate spurious echo artifacts from metabolite signal during a single-voxel acquisition, given that spurious echoes arise from regions outside of the volume of interest.…”

“…In another study, after performing dual‐voxel excitation, reconstruction of separate signals from the left and right hemispheres could be performed based on the sensitivity weighting of the receive coils, thereby accelerating the MRS acquisition by a factor of 2 compared with the sequential acquisition of spectra from each hemisphere 14 . It has also been previously proposed to add phase‐encoding gradients to single‐voxel MRS acquisitions followed by spatial Fourier transformation, to separate the desired region‐of‐interest signal from out‐of‐voxel artifacts 15‐17 . The separation of spectral components from anatomical regions using receive coil information has also been shown using the SPLASH technique 18 …”

Estimation and Removal of spurious echo Artifacts in single-voxel MRS using Sensitivity Encoding

“…In another study, after performing dual-voxel excitation, reconstruction of separate signals from the left and right hemispheres could be performed based on the sensitivity weighting of the receive coils, thereby accelerating the MRS acquisition by a factor of 2 compared to the sequential acquisition of spectra from each hemisphere (14). It has also been previously proposed to add phase-encoding gradients to SV MRS acquisitions followed by spatial Fourier transformation, in order to separate the desired ROI signal from out-of-voxel artifacts (15)(16)(17).…”