The differences between the eigenvalues extracted from different experiments may be related to a number of experimental features (mixing between hyperpolarized and enzyme solutions in the NMR tube, temperature changes during experiments, ...), that possibly affect the robustness of the method. Moreover, performing a large enough number of experiments to get any level of statistical significance is clearly out of reach. Therefore, in an attempt to estimate a global "error" from this set of three experiments, we also computed the average and standard deviation of the trace Λ i of the kinetic matrix of Eq. 1 obtained from the Monte Carlo simulations performed on each realization i of the triplicate experiment. This analysis yielded Λ #1 = -0.27 ± 0.02 s -1 , Λ #2 = -0.31 ± 0.04 s -1 , and Λ #3 = -0.29 ± 0.01 s -1 , respectively. The associated distributions, depicted in Figure (a), show satisfactory agreement.