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.

In vivo 31P NMR studies of rat salivary glands at 6.3 tesla.

In vivo 31P NMR spectra of rat submandibular glands were obtained. The glands were exposed, leaving the neurovascular system intact, and placed in a solenoidal coil. Resonances of nine phosphate metabolites were identified in the spectra and metabolite concentrations were estimated from the corresponding integrals ([ATP] = 3.4 +/- 0.7 mM). Tissue pH, as deduced from the chemical shift of the inorganic phosphate resonance, was 7.26 (+/- 0.07). T1 relaxation times of ATP, phosphocreatine, inorganic phosphate, and phosphomonoester 31P spin systems were examined. The effect of hypoxia was followed as a function of time. 31P NMR spectra of the glands have also been obtained noninvasively by the use of a surface coil, adapted to the dimensions of the glands, and depth pulses.

Fast Fourier imaging.

A new NMR imaging technique, aiming at a reduction of the data acquisition time, is described in detail. The method is applicable in all multidimensional imaging situations where at least one spatial coordinate is resolved. Discussed at some length are the point-spread function, the required bandwidth of the NMR spectrometer, and the sampling strategy used to diminish the loss in signal-to-noise ratio. Experiments reveal that a reduction of the data acquisition time by at least a factor of four is attainable in practice.

Driven-equilibrium radiofrequency pulses in NMR imaging.

Driven-equilibrium pulse techniques are applied to NMR imaging to extend the possibilities of manipulating image contrasts in pulse sequences with a high repetition rate. In many cases the data acquisition time can be much shorter than in more conventional pulse techniques. Both calculations and experiments reveal that the intensity of tissue with slowly relaxing nuclear magnetizations can significantly be enhanced, thus facilitating the detection of a number of pathologies.

Multiple-slice NMR imaging by three-dimensional Fourier zeugmatography.

Multiple-slice NMR images of the human head, obtained by three-dimensional (3-D) Fourier zeugmatography, are presented. Comparison is made with results from 2-D Fourier zeugmatography. The general conclusion is that this multiple-slice technique is an efficient and adequate method for obtaining images of a set of adjacent slices, as long as there are only moderate intensity variations between adjacent slices.