SIMULTANEOUS IN-VIVO SPECTRAL EDITING AND WATER SUPPRESSION

Water suppression is typically performed in vivo by exciting the longi tudinal magnetization in combination with dephasing, or by using frequ ency-selective coherence generation. MEGA, a frequency-selective refoc using technique, can be placed into any pulse sequence element designe d to generate a Hahn spin-echo or stimulated echo, to dephase transver se water coherences with minimal spectral distortions. Water suppressi on 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 ad vantage of the proposed method was exploited for editing J-coupled res onances. Using a double-banded pulse that selectively inverts a J-coup ling partner and simultaneously suppresses water, efficient metabolite editing was achieved in the point resolved spectroscopy (PRESS) and S TEAM sequences in which MEGA was incorporated. To illustrate the effic iency of the method, the detection of gamma-aminobutyric acid (GABA) w as demonstrated, with minimal contributions from macromolecules and ov erlying singlet peaks at 4 T. The estimated occipital GABA concentrati on was consistent with previous reports, suggesting that editing for G ABA is efficient when based on MEGA at high field strengths. (C) 1998 John Wiley & Sons, Ltd.