Optimized detection of changes in glucose-6-phosphate levels in human skeletal muscle by 31P MR spectroscopy

As glucose-6-phosphate (G6P) plays a central role in muscle energy metabolism, the possibility to observe changes in the tissue level of this compound in vivo is very relevant. G6P can be detected noninvasively by (31)P MR spectroscopy, but its visibility in vivo is severely hampered due to low tissue levels and spectral overlap with other, stronger phosphomonoester signals. To optimize the observation of changes in G6P levels in human calf muscle by (31)P MR spectroscopy at 1.5 T, we implemented an approach involving a new RF probe and a postacquisition correction method. An anatomically shaped circularly polarized (31)P coil was designed for high intrinsic sensitivity. Together with an additional (1)H coil and (1)H blocking circuits this allowed the application of NOE and (1)H decoupling to further enhance sensitivity. A hyperglycemic hyperinsulinemic clamp was used to increase G6P levels. The spectra were corrected for frequency and phase drift due to scanner instability and leg movements using an automated phase and frequency correction method. Difference (31)P spectroscopy was applied to detect changes of the G6P signal. The result, in five healthy subjects, demonstrated that the combination of sensitivity optimization with automated drift correction enabled a robust detection of G6P changes in time series experiments down to a resolution of 10 min.