Creatine and phosphocreatine mapping of mouse skeletal muscle by a polynomial and Lorentzian line‐shape fitting CEST method

摘要

Purpose To obtain high‐resolution Cr and PCr maps of mouse skeletal muscle using a polynomial and Lorentzian line‐shape fitting (PLOF) CEST method. Methods Wild‐type mice and guanidinoacetate N‐methyltransferase–deficient (GAMT‐/‐) mice that have low Cr and PCr concentrations in muscle were used to assign the Cr and PCr peaks in the Z‐spectrum at 11.7 T. A PLOF method was proposed to simultaneously extract and quantify the Cr and PCr by assuming a polynomial function for the background and 2 Lorentzian functions for the CEST peaks at 1.95 ppm and 2.5 ppm. Results The Z‐spectra of phantoms revealed that PCr has 2 CEST peaks (2 ppm and 2.5 ppm), whereas Cr only showed 1 peak at 2 ppm. Comparison of the Z‐spectra of wild‐type and GAMT‐/‐ mice indicated that, contrary to brain, there was no visible protein guanidinium peak in the skeletal‐muscle Z‐spectrum, which allowed us to extract clean PCr and Cr CEST signals. High‐resolution PCr and Cr concentration maps of mouse skeletal muscle were obtained by the PLOF CEST method after calibration with in vivo MRS. Conclusions The PLOF method provides an efficient way to map Cr and PCr concentrations simultaneously in the skeletal muscle at high MRI field.