Direct in vivo measurement of human cerebral GABA concentration using MEGA-editing at 7 Tesla

Spectral editing of the GABA spin system is hampered by co-editing of macromolecule (MM) coherences. To reduce contamination arising from MMs in spectra edited for GABA, the highest field strength currently available for human experimentation (7 Tesla) and MEGA-based editing were used. Despite judicious choice of experimental parameters, MM contamination was found to arise from field drifts. When the MM contribution was accounted for, [GABA] = 0.75 +/- 0.14 mumol/g (mean +/- SD, N = 16) relative to 8 mumol/g creatine (Cr), whereas without accounting for the MM signal [GABA*] = 0.88 +/- 0.23 mumol/g (mean SD, N = 16). Incorporating the direct experimental assessment of MM contamination to the edited GABA signal substantially reduced the variance of the measurement, resulting in concentrations that were in excellent agreement with previous C-13 labeling experiments. (C) 2002 Wiley-Liss, Inc.