Detection of glutamate in the human brain at 3 T using optimized constant time point resolved spectroscopy

A CT-PRESS sequence was implemented on a 3-T MR scanner and optimized for the detection of the C4 resonance of glutamate. By simulating the sequence using the full density matrix it was found that 121 chemical shift encoding steps in t(1) with an increment Delta t(1) = 1.6 ms were sufficient to separate the glutamate C4 resonance. The simulations also showed that the highest signal-to-noise ratio was achieved at an average echo time of 131 ms. When using an eightfold undersampling scheme in f(1) in order to reduce the minimum total measurement time, the average echo time was 139 ms with 17 encoding steps (At, = 12.8 ms). The sequence was tested on phantoms containing solutions of various brain metabolites and on healthy human volunteers. Besides resolving glutamate, other resonances detected in vivo comprised N-acetyl aspartate, total creatine, choline containing compounds, and myo-inositol. However, glutamine resonances could not be resolved due to severe signal overlap from glutamate and N-acetyl aspartate.