Homonuclear J‐refocused spectral editing technique for quantification of glutamine and glutamate by 1H NMR spectroscopy

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Abstract
Quantification of the excitatory amino acid of glutamine and glutamate is extremely important partly because, when in excessive amounts, they can produce neuronal damage. However, quantification of such metabolites seems to be not straightforward owing to a large number of metabolic signals, particularly between the 2.0– and 3.0−ppm chemical shift range. The authors investigated a quantification method by using a homonuclear J‐refocused spectral editing technique, namely the J‐refocused PRESS (JPRESS), using both 1.5− and 4‐T whole body NMR systems. At first, the J‐coupling modulation of each metabolite at different TE values using the PRESS and JPRESS pulse sequences was compared. The suppression of J modulations with the JPRESS is well demonstrated on condition that TE values are less than 1/4 J. Then, the accuracy of glutamate quantification after subtracting the two spectra obtained at two different echo times and integrating the difference spectral area at different concentrations was evaluated. The results exhibit an excellent linear relationship between the actual concentration versus the difference spectral peak area at both 1.5 and 4 T. The achievable minimum voxel size was also considered and a 1‐ml voxel size seems to be possible at the typical glutamate concentration in vivo at a field strength of 4 T.