Natural-abundance 13C NMR study of glycogen repletion in human liver and muscle.

Optimizing the surface-coil design and spectral-acquisition parameters has lead to the observation of the 13C NMR natural abundance glycogen signal in man at 2.1 T. Both the human muscle and hepatic glycogen signals can be detected definitively with a time resolution of approximately equal to 13 min. A 1H/13C concentric surface coil was used. The 1H outer coil was 11 cm in diameter; the 13C inner coil was 8 cm in diameter. The coils were tuned to 89.3 MHz and 22.4 MHz, respectively. The 1H coil was used for optimizing field homogeneity (shimming) the magnet and for single-frequency decoupling of the C1 glycogen signal. Total power deposition from both the transmitter pulse and the continuous wave decoupling did not exceed the Food and Drug Administration guideline of 8 W/kg of tissue. Experiments were done for which healthy subjects returned to the magnets at different times for 13C NMR measurement. The spectral difference between experiments was within the noise in the C1 glycogen region. Because of the spectral reproducibility and the signal sensitivity, hepatic glycogen repletion can be followed. Four hours postprandial, hepatic glycogen increases by 3.8 times from the basal fasted state. The hepatic glycogen data correspond directly to previous biopsy results and support the use of 13C NMR as a noninvasive probe of human metabolism.