Fig. 2: Temperature dependency of ¹³C-labeled pyruvate and lactate for hyperpolarized phantom experiments at 7 T compared to thermal calibrations at 11.7 T.

Blood data points (red) show frequency difference of co-polarized [1-¹³C]pyruvate and [1-¹³C]lactate mixed with rodent blood that was preheated to five different temperatures (20–36 °C). For LDH data points, HP [1-¹³C]pyruvate was injected into a buffered solution containing LDH and nicotinamide adenine dinucleotide (NADH) to facilitate lactate production at nine different temperatures ranging from 18–40 °C. Both HP experiments were conducted at in vivo concentrations of 8 mM pyruvate and a linear regression model (not shown) was fit to both datasets. Line plots (5 mM and 100 mM from 11.7 T experiments) show linear regression models to data presented in Fig. 1d for two exemplary concentrations to demonstrate similarity between measurements at 7 T and 11.7 T and different media. Corresponding fit parameters and uncertainties are displayed in Table 1, confidence intervals for 5 mM and 100 mM linear regression fits are too small to depict.