Enhanced detection of glutamate via transverse relaxation encoding with narrowband decoupling in the human brain.

Purpose: This study aims to improve the detection of glutamate (Glu) concentration and T₂ using an enhanced transverse relaxation encoding with narrowband decoupling (TREND) technique.

Methods: A new editing pulse was designed to simultaneously invert both Glu H3 spins (2.12 ppm and 2.05 ppm) while minimizing the excitation of Glu H4. Additionally, a frequency band was created to invert the lactate (Lac) H2 spin (4.10 ppm) while saturating the NAA aspartyl H2 spin (4.38 ppm). Numerical simulations compared Glu and Lac signals using the original and new editing pulses. In vivo experiments were conducted on healthy participants at 7 T to validate this enhanced TREND technique.

Results: Numerical simulations showed prominently enhanced Glu and Lac resonance signals with the new editing pulse. In vivo spectra showed a 47% ± 14% increase in Glu/Cr peak amplitude ratios with the new editing pulse. Using the enhanced TREND sequence, Glu/Cr concentration ratios in the anterior cingulate cortex were 1.03 ± 0.07 with Cramer-Rao lower bounds (CRLBs) of 1.1% ± 0.1%, and Glu T₂ values were 179 ± 18 ms with CRLBs of 1.2% ± 0.1%. The Lac/Cr concentration ratios in the same voxels were 0.05 ± 0.01 with CRLBs of 26% ± 14%, and Lac T₂ values were 196 ± 23 ms with CRLBs of 22% ± 15%.

Conclusion: The new editing pulse significantly enhanced the detection of Glu and enabled the detection of Lac using TREND for measuring both the concentration and T₂ of the markers of oxidative metabolism and glycolysis.