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GABA editing with macromolecule suppression using an improved MEGA‐SPECIAL sequence
Author(s) -
Gu Meng,
Hurd Ralph,
Noeske Ralph,
Baltusis Laima,
Hancock Roeland,
Sacchet Matthew D.,
Gotlib Ian H.,
Chin Frederick T.,
Spielman Daniel M.
Publication year - 2018
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.26691
Subject(s) - mega , in vivo , sequence (biology) , nuclear magnetic resonance , voxel , range (aeronautics) , computer science , chemistry , biophysics , biology , physics , biochemistry , genetics , materials science , artificial intelligence , astronomy , composite material
Purpose The most common γ‐aminobutyric‐acid (GABA) editing approach, MEGA‐PRESS, uses J‐editing to measure GABA distinct from larger overlapping metabolites, but suffers contamination from coedited macromolecules (MMs) comprising 40 to 60% of the observed signal. MEGA‐SPECIAL is an alternative method with better MM suppression, but is not widely used primarily because of its relatively poor spatial localization. Our goal was to develop an improved MM‐suppressed GABA editing sequence at 3 Tesla. Methods We modified a single‐voxel MEGA‐SPECIAL sequence with an oscillating readout gradient for improved spatial localization, and used very selective 30‐ms editing pulses for improved suppression of coedited MMs. Results Simulation and in vivo experiments confirmed excellent MM suppression, insensitive to the range of B 0 frequency drifts typically encountered in vivo. Both intersubject and intrasubject studies showed that MMs, when suppressed by the improved MEGA‐SPECIAL method, contributed approximately 40% to the corresponding MEGA‐PRESS measurements. From the intersubject study, the coefficient of variation for GABA+/Cre (MEGA‐PRESS) was 11.2% versus 7% for GABA/Cre (improved MEGA‐SPECIAL), demonstrating significantly reduced variance ( P = 0.005), likely coming from coedited MMs. Conclusions This improved MEGA‐SPECIAL sequence provides unbiased GABA measurements with reduced variance as compared with conventional MEGA‐PRESS. This approach is also relatively insensitive to the range of B 0 drifts typically observed in in vivo human studies. Magn Reson Med 79:41–47, 2018. © 2017 International Society for Magnetic Resonance in Medicine.