Reproducibility of creatine kinase reaction kinetics in human heart: A ³¹P time-dependent saturation transfer spectroscopy study

Creatine kinase (CK) is essential for the buffering and rapid regeneration of adenosine triphosphate (ATP) in heart tissue. Herein, we demonstrate a ³¹P MRS protocol to quantify CK reaction kinetics in human myocardium at 3 T. Furthermore, we sought to quantify the test-retest reliability of the measured metabolic parameters. The method localizes the ³¹P signal from the heart using modified one-dimensional image-selected in vivo spectroscopy (ISIS), and a time-dependent saturation transfer (TDST) approach was used to measure CK reaction parameters. Fifteen healthy volunteers (22 measurements in total) were tested. The CK reaction rate constant (k_f) was 0.32±0.05 s^-1 and the coefficient of variation (CV) was 15.62%. The intrinsic T₁ for phosphocreatine (PCr) was 7.36±1.79 s with CV=24.32%. These values are consistent with those reported previously. The PCr/ATP ratio was equal to 1.94±0.15 with CV=7.73%, which is within the range of healthy subjects. The reproducibility of the technique was tested in seven subjects and inferred parameters, such as k_f and T₁, exhibited good reliability [intraclass correlation coefficient (ICC) of 0.90 and 0.79 for k_f and T₁, respectively). The reproducibility data provided in this study will enable the calculation of the power and sample sizes required for clinical and research studies. The technique will allow for the examination of cardiac energy metabolism in clinical and research studies, providing insight into the relationship between energy deficit and functional deficiency in the heart.