MOTION-INSENSITIVE LOCALIZED C-13 SPECTROSCOPY USING CYCLIC AND SLICE-SELECTIVE-J CROSS-POLARIZATION

Several new methods are proposed for the sensitive localized detection of C-13 nuclei on the basis of cyclic and slice-selective J cross pol arization in (CHx)-C-13-H-1 spin systems. The C-13 nuclei are detected either directly after the amplitude is enhanced by polarization trans fer in the rotating frame or, preferably, indirectly by heteronuclear editing of signals of the H-1 nuclei coupled to (?)(13)C. In the latte r case, the sensitivity corresponds to that of H-1 rather than to that of C-13 resonance. Test experiments are reported. In vitro applicatio ns to a hen egg and a fresh porcine shank prove the applicability of t he methods to biological objects with C-13 in natural abundance. A par ticular advantage of the new rotating-frame methods over laboratory-fr ame techniques serving the same purpose is the insensitivity to motion s of the object. This is demonstrated by experiments with a moving sam ple. Hartmann/Hahn mismatch can be compensated using the MOIST modific ation. The time-averaged absorbed radiofrequency power per kilogram bo dy weight was estimated on the basis of a model for surface power abso rption. The result lies well below the standard safety limits for clin ical applications. (C) 1994 Academic Press, Inc.