Simultaneous Detection of GABA and Glycine Using MEGA-PRESS With TE Optimization at 3T
Justin R Singer1,2, Kimberly L Chan1,2,3
1Department of Biomedical Engineering, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Purpose:
To achieve the simultaneous acquisition of gamma-aminobutyric acid (GABA) and glycine (Gly) using a MEGA-PRESS sequence with an optimized TE at 3T.
Methods:
MEGA-PRESS simulations were performed at TEs 60-88 ms to determine the optimal TE for Gly detection with minimal myo-Inositol (mI) overlap and maximal GABA detection sensitivity. MEGA-PRESS data were acquired in the occipital lobe of 6 healthy subjects at TEs of 64 and 68 ms. GABA+ levels, between-acquisition (SUM (edit-ON+edit-OFF) and edit-OFF) and inter-subject coefficient-of-variation (CVs) and mI, Gly, and glucose CRLBs were evaluated to assess fit reliability. The residuals of the edit-OFF and SUM fits were compared with and without Gly in the basis set to examine the effect of Gly on fit accuracy and metabolite quantification.
Results:
Simulations indicated that optimal Gly detection with minimal overlap from mI is observed at a TE of 64 ms. Simulations and in vivo experiments indicate that this TE resulted in no reduction in GABA+ sensitivity relative to the commonly used TE of 68 ms. Gly between-acquisition and inter-subject CVs and CRLBs were substantially lower at a TE of 64 ms than at a TE 68 ms. Spectral fits with Gly excluded from the basis set resulted in a significant increase in CRLBs and fit residuals for mI and glucose at a TE of 64 ms, but not at a TE of 68 ms.
Conclusion:
The simultaneous detection of GABA+ from the difference spectrum and Gly from the edit-OFF/SUM spectra is possible using a MEGA-PRESS sequence at a TE of 64 ms.
