Elimination of spatial interference in PRESS-localized editing spectroscopy.

Unambiguous detection of gamma-amino butyric acid (GABA) in the human brain is hindered by low concentration and spectral overlap with other metabolites. The popular MEGA-PRESS (PRESS: point-resolved spectroscopic sequence) method allows spectral separation of GABA from other metabolites, but suffers from a significant signal-to-noise ratio (SNR) reduction due to the 4-compartment artifact. An alternative PRESS localization technique (PRESS+4) was investigated and compared to MEGA-PRESS using numerical simulations, phantom, and in vivo experiments. It was shown that while the MEGA-PRESS method suffers significant signal loss ( approximately equal 20% for the difference spectrum), GABA signal intensity in PRESS+4 is reduced by only 2% compared to the nonlocalized condition at 4T. The improved method retains important features of the popular MEGA-PRESS such as additional water suppression and macromolecular elimination as demonstrated in human brain experiments. This method is not limited to GABA J-difference editing, but can be applied in any PRESS-based experiments. It should prove particularly useful at higher field, where the 4-compartment artifact is especially detrimental.