Simultaneous edited MRS of GABA and glutathione

Abstract

Edited MRS allows the detection of low-concentration metabolites, whose signals are not resolved in the MR spectrum. Tailored acquisitions can be designed to detect, for example, the inhibitory neurotransmitter γ-aminobutyric acid (GABA), or the reduction-oxidation (redox) compound glutathione (GSH), and single-voxel edited experiments are generally acquired at a rate of one metabolite-per-experiment. We demonstrate that simultaneous detection of the overlapping signals of GABA and GSH is possible using Hadamard Encoding and Reconstruction of Mega-Edited Spectroscopy (HERMES). HERMES applies orthogonal editing encoding (following a Hadamard scheme), such that GSH- and GABA-edited difference spectra can be reconstructed from a single multiplexed experiment. At a TE of 80ms, 20-ms editing pulses are applied at 4.56ppm (on GSH),1.9ppm (on GABA), both offsets (using a dual-lobe cosine-modulated pulse) or neither. Hadamard combinations of the four sub-experiments yield GABA and GSH difference spectra. It is shown that HERMES gives excellent separation of the edited GABA and GSH signals in phantoms, and resulting edited lineshapes agree well with separate Mescher-Garwood Point-resolved Spectroscopy (MEGA-PRESS) acquisitions. In vivo, the quality and signal-to-noise ratio (SNR) of HERMES spectra are similar to those of sequentially acquired MEGA-PRESS spectra, with the benefit of saving half the acquisition time.

Keywords: Editing; GABA; Glutathione; HERMES; Hadamard; Simultaneous.