¹H-NMR Chemical Shifts and Coupling Constants for Brain Metabolites

Improved resolution of glutamate, glutamine and γ‐aminobutyric acid with optimized point‐resolved spectroscopy sequence timings for their simultaneous quantification at 9.4 T

“…Proton ( 1 H) magnetic resonance spectroscopy (MRS) enables the non‐invasive biochemical analysis and measurements of metabolites in vivo . Glu and Gln can both be described as AMNPQ spin systems, where the P and Q spins refer to the C4 protons and resonate at ≈2.35 and ≈2.45 ppm for Glu and Gln, respectively . The C4 protons are often employed to quantify Glu and Gln or their collective levels (Glx) by MRS .…”

“…The C4 protons are often employed to quantify Glu and Gln or their collective levels (Glx) by MRS . The concentration of Gln is ≈3.0–5.8 mmol/kg ww (less than the Glu concentration of ≈6.0–12.5 mmol/kg ww ) in healthy human brain, and its signal at ≈2.45 ppm is overlapped by that of Glu at ≈2.35 ppm and by that of N ‐acetylaspartate (NAA) protons resonating at ≈2.49 ppm. GABA can be described as an A 2 M 2 X 2 spin system, with the C2 protons (X spins) resonating at ≈2.28 ppm.…”

Temperature dependence of 1H NMR chemical shifts and its influence on estimated metabolite concentrations

“…Subsequently, the chemical shift values were determined by a C++ program using a simplex algorithm. This optimisation procedure minimised the difference between the experimental and fitted spectra calculated by the GAMMA NMR library [41] and using the J-coupling constants published in [12,13] as prior knowledge. Downfield signals were neglected because their in vivo observation is hampered for most metabolites by short T 2 , exchange processes with water, and overlapping with other resonances [12,43].…”

“…The basis sets of metabolite profiles were simulated for the upfield range using the chemical shifts and J-coupling constants for 37 °C [12,13] or the temperature matched chemical shift values for other temperatures. All basis sets were simulated for a constant concentration.…”

“…Thus, well established quantification programs such as LCModel [8], QUEST [9,10], or AQSES [11] use a model function for each metabolite to minimise the number of variables during the fitting procedure. These model functions are either measured on phantom solutions or simulated using published values of chemical shifts and J-coupling constants as prior knowledge [12,13]. The similarities and differences between AQSES, which was used in this study, and other quantification methods have been described by Poullet et al [11].…”