Water suppression in the human brain with hypergeometric RF pulses for single-voxel and multi-voxel MR spectroscopy.

Abstract

To develop and investigate a novel water suppression sequence with hypergeometric pulses at 3 T. Simulations were used to optimize the delays and amplitudes of 5 hypergeometric prepulses, to minimize the residual water over a range of T1 and B1 values. Single-voxel data with hypergeometric water suppression (HGWS) prepulses were acquired in the centrum semiovale, 2 parietal regions, and insula of 7 subjects, and compared with VAPOR water suppression. Magnetic resonance spectroscopic imaging (MRSI) data using both VAPOR and HGWS prepulses were also collected and compared. Water suppression performance was calculated as the residual water peak height relative to the unsuppressed water peak. MRSI voxel-by-voxel comparison was performed by calculating the ratio between HGWS and VAPOR residual water peaks. In simulations, HGWS and VAPOR are insensitive to B1 and water T1 variations, but with no B1 variation, HGWS has a lower average residual water fraction (0.0033) than that of VAPOR (0.0091). In single-voxel acquisitions, HGWS performs better than VAPOR in all regions with a 2.3-fold to 5.7-fold lower residual water. In MRSI acquisitions, HGWS performs on average 2.3-fold better than VAPOR in 98.9% of the voxels. HGWS provides better water suppression than VAPOR in both single-voxel and multivoxel acquisitions with a shorter sequence duration.