Simultaneousin vivo spectral editing and water suppression

Abstract

Water suppression is typically performed in vivo by exciting the longitudinal magnetization in combination with dephasing, or by using frequency-selective coherence generation. MEGA, a frequency-selective refocusing technique, can be placed into any pulse sequence element designed to generate a Hahn spin-echo or stimulated echo, to dephase transverse water coherences with minimal spectral distortions. Water suppression performance was verified in vivo using stimulated echo acquisition mode (STEAM) localization, which provided water suppression comparable with that achieved with four selective pulses in 3,1-DRYSTEAM. The advantage of the proposed method was exploited for editing J-coupled resonances. Using a double-banded pulse that selectively inverts a J-coupling partner and simultaneously suppresses water, efficient metabolite editing was achieved in the point resolved spectroscopy (PRESS) and STEAM sequences in which MEGA was incorporated. To illustrate the efficiency of the method, the detection of g-aminobutyric acid (GABA) was demonstrated, with minimal contributions from macromolecules and overlying singlet peaks at 4 T. The estimated occipital GABA concentration was consistent with previous reports, suggesting that editing for GABA is efficient when based on MEGA at high field strengths.

High-field proton magnetic resonance spectroscopy reveals metabolic effects of normal brain aging

“…For example, sequences are now available to quantify NAAG, GABA, Asc, and GSH on 3T clinical scanners (Choi et al, 2011; Edden et al, 2007; Mescher et al, 1998). Thus, it would be feasible to translate noninvasive 1 H-MRS findings in animal models of aging to human studies using existing clinical scanners and sequences.…”

The increase in medial prefrontal glutamate/glutamine concentration during memory encoding is associated with better memory performance and stronger functional connectivity in the human medial prefrontal–thalamus–hippocampus network

“…To ensure goodness of fit, any cases where shimming resulted in FWHM >20 Hz were rejected. Single‐volume, MEGA point‐resolved spectroscopy (PRESS), J‐difference editing sequence was used to measure GABA and glutamate/glutamine (Mescher, Merkle, Kirsch, Garwood, & Gruetter, 1998). For each spectrum (edit on and edit off), 128 spectral scans were acquired (TR = 1600 ms, TE = 68 ms,).…”

Individual Differences in the Balance of GABA to Glutamate in pFC Predict the Ability to Select among Competing Options

“…GABA was measured using a “J-editing” technique (MEGA-PRESS; Mescher, Merkle, Kirsch, Garwood, & Gruetter, 1998) implemented in-house by modification of GE’s standard PROBE-P sequence (presscsi) with the addition of two spectrally selective 180° Gaussian pulses of 16-msec duration, centered at 1.9 ppm, as previously described (Rojas, Singel, Steinmetz, Hepburn, & Brown, 2013). Using standard spectroscopy, GABA resonances at 3.02 ppm are masked by the creatine peak as they have similar resonance frequencies.…”