Regional GABA Measurement Protocol

In order to compare the correction factors, a dataset was analyzed in which 5 regional GABA measurements have been made in 16 healthy volunteers. This study was approved by the local IRB and all volunteers provided informed, written consent. All scanning was performed at 3T (‘Achieva’, Philips Healthcare, The Netherlands) with a 32-channel head coil. Scanning included a T1-weighted whole brain image, (MPRage, TR/TE = 8 ms/3.7 ms, 1 mm³ isotropic voxels) and single voxel GABA-edited MRS in 5 voxel locations (visual cortex, OCC, auditory cortex, AUD, sensorimotor cortex, SM, frontal eye fields, FEF and dorsolateral prefrontal cortex, DLPFC). All voxels were 3 × 3 × 3 cm³, except for the AUD which was 4 × 3 × 2 cm³. The GABA-edited MRS was collected using a MEGA-PRESS experiment (19 (link)). Editing pulses were applied at 1.9 ppm and 7.46 ppm, interleaving every two transients across a 16-step phase cycle, TR/TE = 2s/68 ms; 320 transients, 2048 data points at a spectra width of 2 kHz; VAPOR water suppression and first-order and second-order shim parameters were derived using pencil-beam projection-based shimming routine. The limited selectivity of the editing pulses (14 ms duration) results in co-editing of macromolecules (MM), thus quantified GABA includes MM contamination, often referred to as GABA+.