Simultaneous Detection of GABA and Glycine Using MEGA‐PRESS With TE Optimization at 3T

TL;DR

This paper shows how to detect two brain chemicals, GABA and glycine, at the same time using an optimized MRI technique.

Contribution

The study introduces an optimized echo time (TE) of 64 ms for simultaneous detection of GABA and glycine using MEGA-PRESS at 3T.

Findings

A TE of 64 ms minimizes myo-Inositol overlap and maintains GABA detection sensitivity.

Using TE 64 ms results in lower variability and better reliability for glycine detection compared to TE 68 ms.

Excluding glycine from the basis set increases fit errors at TE 64 ms but not at TE 68 ms.

Abstract

To achieve the simultaneous acquisition of gamma‐aminobutyric acid (GABA) and glycine (Gly) using a MEGA‐PRESS sequence with an optimized TE at 3T.

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.

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.

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.

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