Rapid 3D Saturation Transfer Imaging for Simultaneous Phosphocreatine and Glycogen Mapping in Human Muscle.

Objective: Phosphocreatine (PCr) and glycogen are key metabolites underpinning the skeletal muscle contractions. Simultaneous 3D imaging of these metabolites is valuable for understanding heterogeneous energetic events. While saturation transfer (ST) MRI can detect metabolites, 3D ST acquisition generally requires long scan times. We developed a rapid, high-resolution 3D scanning scheme for simultaneous quantification of PCr and glycogen.

Methods: A 3D sequence was implemented on a 5 T MR scanner, using a continuous-wave saturation pulse and golden-angle stack-of-stars readouts. A patch-based low-rank algorithm was incorporated to reduce scan time. The sensitivity of sequence to concentration variations was validated in phantom experiments, and metabolite distribution was assessed in vivo. Furthermore, exercise protocols were employed to investigate metabolic heterogeneity.

Results: The optimized acquisition strategy reduced the scan time to 26.7% of full sampling. Phantom studies showed a linear correlation between contrast signals and metabolite concentrations, in-vivo studies demonstrated uniform PCr and glycogen distribution across slices. Post-exercise, PCr and glycogen depletion was clearly observed.

Conclusion And Significance: The 3D rapid ST imaging framework achieves 100 mm coverage of skeletal muscle in 11.2 minutes, showing the potential to monitor muscle physiological processes.