Quantification of creatine kinase reaction rate in mouse hindlimb using phosphorus-31 magnetic resonance spectroscopic fingerprinting

Abstract. The goal of this study was to evaluate the accuracy, reproducibility, and efficiency of a ³¹P magnetic resonance spectroscopic fingerprinting ( ³¹P-MRSF) method for fast quantification of the forward rate constant of creatine kinase (CK) in mouse hindlimb. The ³¹P-MRSF method acquired spectroscopic fingerprints using interleaved acquisition of phosphocreatine (PCr) and γATP with ramped flip angles and a saturation scheme sensitive to chemical exchange between PCr and γATP. Parameter estimation was performed by matching the acquired fingerprints to a dictionary of simulated fingerprints generated from the Bloch-McConnell model. The accuracy of ³¹P-MRSF measurements was compared with the magnetization transfer (MT-MRS) method in mouse hindlimb at 9.4 T (n = 8). The reproducibility of ³¹P-MRSF was also assessed by repeated measurements. Estimation of the CK rate constant using ³¹P-MRSF (0.39 ± 0.03 s ⁻¹) showed a strong agreement with that using MT-MRS measurements (0.40 ± 0.05 s ⁻¹). Variations less than 10% were achieved with 2 min acquisition of ³¹P-MRSF data. Application of the ³¹P-MRSF method to mice subjected to an electrical stimulation protocol detected an increase in CK rate constant in response to stimulation-induced muscle contraction. These results demonstrated the potential of the ³¹P-MRSF framework for rapid, accurate, and reproducible quantification of the chemical exchange rate of CK in vivo.