ACE: a single-shot method for water-suppressed localization and editing of spectra, images, and spectroscopic images

A versatile method for localized (1H) NMR spectroscopy is presented. The method intrinsically combines B0-based spatial localization with the possibility of water suppression and spectral editing. With this sequence it is feasible to localize not only single spectra but also phase-encoded images and spectroscopic images. The technique essentially integrates the "Hahn spin-echo" with the "stimulated echo" sequence and is therefore called ACE (acquiring combined echoes). It realizes water-suppressed three-dimensional localization in a single shot and can be used for localized shimming. Studies in which the new method is applied to phantoms with metabolites diluted at low concentrations are presented. Discrimination between lactate and alanine, employing an adapted spectral editing method with complete inversion, combined with simultaneous water suppression and localization of a 0.06-cc volume is shown. The suppression of signals from outside the selected volume is greater than or equal to 24,000. Also, the method is demonstrated by in vivo experiments at 6.3 T. Localized water-suppressed 1H spectra are obtained completely noninvasively, leaving scalp and fur intact, from well-defined volumes of 0.15 cc in the brain of a living rat. Water-suppressed spectroscopic imaging over a localized volume with "body" coil excitation and noninvasive surface coil detection yielded spectra from voxels as small as 25 microliters in the in vivo rat brain.