Motion-insensitive volume-selective pulse sequences for direct and proton-detected 13C spectroscopy: detection of glycogen in the human liver in vivo.
Two compact pulse sequences are reported for the volume-selective detection of 13C nuclei. 13C signals are either directly acquired after enhancing the amplitude by polarization transfer from the coupled protons or, preferably, indirectly detected by heteronuclear editing of proton signals of 1H nuclei coupled to 13C. In the latter case, the full sensitivity of proton resonance is achieved, and signals from uncoupled protons or protons coupled to non-13C nuclei or 13C nuclei of undesired compounds are suppressed. Both sequences are single-scan procedures and are insensitive to the pulse phases and to motions of the investigated organs. The insensitivity to organ motions is due to the extremely compact character of these sequences avoiding coherence evolution periods as far as possible. This is achieved first by the introduction of double-resonance sandwich (DORSA) pulses accomplishing the polarization transfer slice selectively in a very short time. The second reason is that the initial evolution interval which is usually part of polarization transfer experiments is avoided by the aid of a doublet line-selective inversion pulse. Several test experiments in vivo are reported. In particular, it is demonstrated that glycogen can be detected in natural abundance in the human liver in vivo using a 2-T whole-body tomograph even without the use of heart or respiration triggers. The total acquisition time was 22 min, and a signal-to-noise ratio of 6 was achieved.