Chemical exchange rotation transfer imaging of phosphocreatine in muscle.

In chemical exchange saturation transfer (CEST) imaging, the signal at 2.6 ppm from the water resonance in muscle has been assigned to phosphocreatine (PCr). However, this signal has limited specificity for PCr since the signal is also sensitive to exchange with protein and macromolecular protons when using some conventional quantification methods, and will vary with changes in the water longitudinal relaxation rate. Correcting for these effects while maintaining reasonable acquisition times is challenging. As an alternative approach to overcome these problems, here we evaluate chemical exchange rotation transfer (CERT) imaging of PCr in muscle at 9.4 T. Specifically, the CERT metric, AREX at 2.6 ppm, was measured in solutions containing the main muscle metabolites, in tissue homogenates with controlled PCr content, and in vivo in rat leg muscles. PCr dominates CERT metrics around 2.6 ppm (although with nontrivial confounding baseline contributions), indicating that CERT is well-suited to PCr specific imaging, and has the added benefit of requiring a relatively small number of acquisitions.