Purpose To separately measure N‐acetyl aspartul glutamate (NAAG), N‐acetyl aspartate (NAA), aspartate (Asp), and glutamate (Glu) concentrations in white matter (WM) using J‐editing techniques in patients with mild traumatic brain injury (mTBI) in the acute phase. Methods Twenty‐four patients with closed concussive head injury and 29 healthy volunteers were enrolled in the current study. For extended 1H MRS examination, patients and controls were equally divided into two subgroups. In subgroup 1 (12 patients/15 controls), NAAG and NAA concentrations were measured in WM separately with MEGA‐PRESS (echo time/repetition time [TE/TR] = 140/2000 ms; δONNAA/ δOFFNAA = 4.84/4.38 ppm, δONNAAG/ δOFFNAAG = 4.61/4.15 ppm). In subgroup 2 (12 patients/14 controls), Asp and Glu concentrations were acquired with MEGA‐PRESS (TE/TR = 90/2000 ms; δONAsp/ δOFFAsp = 3.89/5.21 ppm) and TE‐averaged PRESS (TE from 35 ms to 185 ms with 2.5‐ms increments; TR = 2000 ms) pulse sequences, respectively. Results tNAA and NAAG concentrations were found to be reduced, while NAA concentrations were unchanged, after mild mTBI. Reduced Asp and elevated myo‐inositol (mI) concentrations were also found. Conclusion The main finding of the study is that the tNAA signal reduction in WM after mTBI is associated with a decrease in the NAAG concentration rather than a decrease in the NAA concentration, as was thought previously. This finding highlights the importance of separating these signals, at least for WM studies, to avoid misinterpretation of the results. NAAG plays an important role in selectively activating mGluR3 receptors, thus providing neuroprotective and neuroreparative functions immediately after mTBI. NAAG shows potential for the development of new therapeutic strategies for patients with injuries of varying severity.

Purpose: To measure the transverse relaxation rate (T 2 ) of aspartate (Asp) from Asp-edited MEGA-PRESS spectra and use the measured T 2 values to estimate the Asp concentrations in gray matter (GM)-and white matter (WM)-dominant brain regions. Methods: Since Asp-edited MEGA-PRESS spectra contain non-overlapped Asp signals, TE-dependence arising from J-evolution can be considered using phantom MEGA-PRESS spectra acquired with the same parameters as in vivo spectra. Four TE values (90, 115, 140, and 150 ms) were selected from numeric analyses for effective detection of the edited Asp multiplet at ~2.71 ppm. The T 2 relaxation time was measured in the anterior cingulate cortex (ACC) of 16 healthy volunteers. Absolute cerebral Asp concentrations were measured with Asp-edited MEGA-PRESS in the ACC and left centrum semiovale (CS) of 44 healthy volunteers at TEs of 90, 115, 140, and 150 ms. Results: The in vivo and phantom T 2 values of the edited Asp signals were 165 ± 37ms and 313 ± 27 ms, respectively. The cortical GM concentration quantified was significantly greater than the WM concentration (2.80 ± 0.31 mM vs. 1.01 ± 0.18 mM). Conclusion: MEGA-PRESS is the most common editing method used for lowconcentration metabolites detection. Estimation of the absolute Asp concentrations has potential in many research applications, such as studying the processes underlying the reduction of N-acetyl aspartate as well as studying mitochondrial diseases etc.The T 2 measurement method described has been successfully applied for edited Asp signals. This method can also be used for other strongly J-coupled signals. K E Y W O R D S1 H MRS, 3 T, aspartate, gray matter, J-coupled metabolites, MEGA-PRESS, relaxation rate (T 2 ), white matter 12 | MENSHCHIKOV Et al.