Localized, gradient‐reversed ultrafast z‐spectroscopy in vivo at 7T. Issue 4 (1st July 2016)

• Record Type: Journal Article
• Authors: Wilson, Neil E.; D'Aquilla, Kevin; Debrosse, Catherine; Hariharan, Hari; Reddy, Ravinder
• Is Part Of: Magnetic resonance in medicine. Volume 76:Issue 4(2016)
• Page Start: 1039
• Page End: 1046
• Publication Date: 2016-07-01
• Subjects: GRUFZS -- ultrafast z‐spectroscopy -- CEST -- brain -- high field -- glutamate; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.26314
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: To collect ultrafast z‐spectra in vivo in situations where voxel homogeneity cannot be assured. Theory: Saturating in the presence of a gradient encodes the frequency offset spatially across a voxel. This encoding can be resolved by applying a similar gradient during readout. Acquiring additional scans with the gradient polarity reversed effectively mirrors the spatial locations of the frequency offsets so that the same physical location of a positive offset in the original scan will contribute a negative offset in the gradient‐reversed scan. Methods: Gradient‐reversed ultrafast z‐spectroscopy (GRUFZS) was implemented and tested in a modified, localized PRESS sequence at 7T. Lysine phantoms were scanned at various concentrations and compared with coventionally‐acquired z‐spectra. Scans were acquired in vivo in human brain from homogeneous and inhomogeneous voxels with the ultrafast direction cycled between read, phase, and slice . Results were compared to those from a similar conventional z‐spectroscopy PRESS‐based sequence. Results: Asymmetry spectra from GRUFZS are more consistent and reliable than those without gradient reversal and are comparable to those from conventional z‐spectroscopy. GRUFZS offers significant acceleration in data acquisition compared to traditional chemical exchange saturation transfer methods with high spectral resolution and showed higher relative SNR effficiency. Conclusion: GRUFZS offers a method of collecting ultrafast z‐spectra in voxels with the inhomogeneity often found in vivo. Magn Reson Med 76:1039–1046, 2016. © 2016 Wiley Periodicals, Inc.