Single-shot two-echo technique for simultaneous measurement of GABA and creatine in the human brain in vivo

Abstract

A single-shot, two-echo method for the simultaneous detection of multiple-quantum (MQ)-filtered γ-aminobutyric acid (GABA) and creatine (Cr) was developed and demonstrated in the human brain in vivo at 3 Tesla. The simultaneously measured Cr singlet served as a navigator for the spectral phase of GABA and any frequency shift during measurements due to drift in the static magnetic field (B0) or subject movement, as well as an internal concentration reference. In addition, the use of a double-band frequency-selective MQ filter for C3 and C4 methylene protons of GABA provided a very robust measurement of GABA, with excellent suppression of overlapping metabolites such as Cr and glutathione (GSH) in each single scan. Contamination from overlapping macromolecules was also demonstrated to be negligible with this method. The GABA-to-Cr ratio was 0.09 ± 0.03 (mean ± SD, N = 17) and the estimated concentration of GABA in the frontoparietal region of the human brain in vivo was 0.66 ± 0.19 μmol/g (mean ± SD, N = 17) with the internal reference method, and 0.69 ± 0.18 μmol/g (mean ± SD, N = 17) with the external reference method. The observed pattern of GABA doublet was consistent among all subjects, with a frequency separation of ∼13 Hz.