Two-dimensional, J-resolved spectroscopic imaging of GABA at 4 Tesla in the human brain.

A method for measuring brain gamma-amino butyric acid (GABA) levels is presented that combines 2D J-resolved magnetic resonance spectroscopy (J-MRS) techniques with chemical-shift imaging (2D-JMRSI) at 4 Tesla (T). The results of phantom and in vivo experiments agree well in demonstrating that the (2)CH(2) GABA resonance situated at 2.97 ppm can be resolved from the neighboring creatine (Cr) resonance at 3.03 ppm and quantified. Single-voxel, J-resolved standard and metabolite-nulled in vivo experiments on six healthy subjects reveal a broad component from the underlying macromolecules (MM) that resonates at and around 3.00 ppm, which is estimated to contribute approximately 15% to the J-resolved GABA resonance in this large voxel at a repetition time (TR) of 4.5 s. With our 2D-JMSRI at 1.25 s TR, the macromolecule resonance contribution to our GABA measurements is approximated to be 12%. Six healthy human subjects underwent scanning at 4T with this sequence, yielding a global brain GABA concentration of 0.76 +/- 0.20 mM after correction for 12% macromolecule contribution.