Gamma‐aminobutyric acid edited echo‐planar spectroscopic imaging (EPSI) with MEGA‐sLASER at 7T

Purpose: For rapid spatial mapping of gamma‐aminobutyric acid (GABA) at the
increased sensitivity and spectral separation for ultra‐high magnetic field strength (7
tesla [T]) an accelerated edited magnetic resonance spectroscopic imaging technique
was developed and optimized for the human brain at 7 T.
Methods: A MEGA‐sLASER sequence was used for GABA editing and volume
selection to maximize editing efficiency and minimize chemical shift displacement
errors. To accommodate the high bandwidth requirements at 7 T, a single‐shot echo
planar readout was used for rapid simultaneous encoding of the temporal dimension
and 1 spatial. B0 and B1 field aspects specific for 7 T were studied together with correction
procedures, and feasibility of the EPSI MEGA‐sLASER technique was tested
in vivo in 5 healthy subjects.
Results: Localized edited spectra could be measured in all subjects giving spatial
GABA signal distributions over a central brain region, having 45‐ to 50‐Hz spatial
intervoxel B0 field variations and up to 30% B1 field deviations. MEGA editing was
found unaffected by the B0 inhomogeneities for the optimized sequence. The correction
procedures reduced effects of intervoxel B0 inhomogeneities, corrected for spatial
editing efficiency variations, and compensated for GABA resonance phase and
frequency shifts from subtle motion and acquisition instabilities. The optimized oscillating
echo‐planar gradient scheme permitted full spectral acquisition at 7 T and
exhibited minimal spectral‐spatial ghosting effects for the selected brain region.
Conclusion: The EPSI MEGA‐sLASER technique was shown to provide time‐efficient
mapping of regional variations in cerebral GABA in a central volume of interest
with spatial B1 and B0 field variations typical for 7 T.