Measurement of N-acetylaspartylglutamate in Human Brain by Difference Editing at 7.0 Tesla

INTRODUCTION N-acetylaspartylglutamate (NAAG) is structurally similar to N-acetylaspartate (NAA) and glutamate (Glu). Due to its relatively low concentration (0.5 – 2 mM) and the overlap with abundant multiplets of NAA and Glu, NAAG in human brain is difficult to measure. The most prominent peak is a singlet of the acetyl protons at 2.04 ppm [1], but this signal overlaps with the NAA singlet at 2.01 ppm. The estimation of this NAAG singlet is further complicated by the overlap with the C3-proton multiplets of Glu, glutamine, glutathione and the NAAG Glu moiety at ~2 ppm. Excellent shimming enabled measurement of the NAAG singlet at 2T [2]. A difference editing (MEGA) [3] approach to measure NAAG at 3T has been reported recently [4], which utilized the spectral difference between the aspartyl (Asp) groups of NAAG and NAA. Editing approach for NAAG measurement is relatively new. Here, we report measurements of NAAG and NAA in the human frontal brain by the difference editing at 7T.