Simultaneousin vivo spectral editing and water suppression

TLDR

Water suppression in vivo is usually achieved by exciting longitudinal magnetization with dephasing or by frequency‑selective coherence generation, and the MEGA technique can be incorporated into any pulse sequence element to dephase transverse water coherences with minimal spectral distortion. The authors exploit this capability to edit J‑coupled resonances. They verified water suppression in vivo using STEAM localization, achieving performance comparable to four selective pulses in 3,1‑DRYSTEAM, and employed a double‑banded pulse that simultaneously inverts a J‑coupling partner and suppresses water to enable efficient metabolite editing in PRESS and STEAM sequences. The method enabled clear detection of γ‑aminobutyric acid at 4 T with minimal macromolecule contamination, and the estimated occipital GABA concentration matched previous reports, demonstrating efficient high‑field editing. © 1998 John Wiley & Sons, Ltd.

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 γ-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. © 1998 John Wiley & Sons, Ltd.