Simultaneous mapping of glycogen and phosphocreatine in human skeletal muscle by saturation transfer MRI

Glycogen and phosphocreatine (PCr) are essential metabolites for maintaining cellular ATP levels. Recent reports show the possibility of PCr mapping in skeletal muscle using CEST MRI but glycogen levels measured using this approach have been inconclusive. Here we report the high-resolution mapping of glycogen and PCr in human skeletal muscle based on relayed nuclear Overhauser effects (glycoNOE) and CEST, respectively. Results at 5T show homogeneous distributions of glycogen and PCr in the calf at levels corresponding to biopsy. Exciting possible applications include localized studies of cellular energetics and noninvasive in situ evaluation of exercise and muscle metabolism in humans.