Method for high-resolution imaging of creatine in vivo using chemical exchange saturation transfer

摘要

Purpose To develop a chemical exchange saturation transfer (CEST)-based technique to measure free creatine (Cr) and to validate the technique by measuring the distribution of Cr in muscle with high spatial resolution before and after exercise. Methods Phantom studies were performed to determine contributions from other Cr kinase metabolites to the CEST effect from Cr (CrCEST). CEST, T2, magnetization transfer ratio and 31P magnetic resonance spectroscopy acquisitions of the lower leg were performed before and after plantar flexion exercise on a 7T whole-body magnetic resonance scanner on healthy volunteers. Results Phantom studies demonstrated that while Cr exhibited significant CEST effect there were no appreciable contributions from other metabolites. In healthy human subjects, following mild plantar flexion exercise, increases in the CEST effect from Cr were observed, which recovered exponentially back to baseline. This technique exhibited good spatial resolution and was able to differentiate differences in muscle utilization among subjects. The CEST effect from Cr results were compared with 31P magnetic resonance spectroscopy results showing good agreement in the Cr and phosphocreatine recovery kinetics. Conclusion Demonstrated a CEST-based technique to measure free Cr changes in in vivo muscle. The CEST effect from Cr imaging can spatially map changes in Cr concentration in muscle following mild exercise. This may serve as a tool for the diagnosis and treatment of various disorders affecting muscle.