Simultaneous Quantification of Glutamate and Glutamine by J-modulated Spectroscopy at 3 Tesla

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Abstract

Purpose:

The echo time (TE) averaged spectrum is the one-dimensional (1D) cross-section of the J-resolved spectrum at J = 0. In multiecho TE-averaged spectroscopy, glutamate (Glu) is differentiated from glutamine (Gln) at 3 Tesla (T). This method, however, almost entirely suppresses Gln resonance lines around 2.35 ppm, leaving Gln undetermined. This study presents a novel method for quantifying both Glu and Gln using multi-echo spectral data.

Methods:

A 1D cross-section of J-resolved spectroscopy at J = 7.5 Hz—referred to as J-modulated spectroscopy—was developed to simultaneously quantify Glu and Gln levels in the human brain. The transverse relaxation times (T2s) of metabolites were first determined using conventional TE-averaged spectroscopy with different starting echo time and then incorporated into the spectral model for fitting J-modulated data.

Results:

Simulation and in vivo data showed that the resonance signals of Glu and Gln were clearly separated around 2.35 ppm in J-modulated spectroscopy. In the anterior cingulate cortex, both Glu and Gln levels were found to be significantly higher in gray matter than in white matter in healthy subjects (P < 10−10 and < 10−5, respectively).

Conclusion:

Gln resonances can be clearly separated from Glu and N-acetyl-aspartate around 2.35 ppm using J-modulated spectroscopy. This method can be used to quantitatively measure Glu and Gln simultaneously at 3T. Magn Reson Med 76:725–732, 2016. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

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