Dynamic nuclear polarization of the substrates was performed using a HyperSense system (Oxford Instruments Molecular Biotools, Oxford, UK) operating at 1.4 K and using a microwave power of 25 mW. For the lactate sample, 75 mg of 1.7-M sodium lactate in 37.5:62.5 w/w water:glycerol with 15-mM OX063 were mixed with approximately 7 μL of a 1:50-solution of Dotarem. Dissolution with 4 g of 40 mM Tris pH 7.6 containing 100-mg/L disodium EDTA yielded a final polarized solution of 33-mM lactate. Sample preparation and solvent for the 80-mM pyruvate solution was the same as previously described (23 (link)). The build-up time constant for the solid state polarization of lactate was on the order of 2800 s, almost three times a long as for pyruvate (1100 s). Whereas the polarization of the pyruvate samples had very little variation, 23.5% ± 0.5% (mean ± standard deviation (sd)), n = 6), the polarization of the lactate samples ranged from 15% to 31% with an average value of 25.3% ± 5.5% (n=12). The liquid-state polarization was estimated from the solid-state polarization build-up curve (scale in arbitrary units) for each sample and independent calibration experiments in which the liquid-state polarization of a sample was measured in the MR scanner. A pulse-and-acquire sequence (5.625° hard pulse, spectral width (SW) = 5000 Hz, TR = 3 s, N = 80) was used to measure the longitudinal relaxation constant of the hyperpolarized sample, which was then used to extrapolate the signal intensity to the time of dissolution. After doping the sample with a relaxation agent (10 μL/mL, Magnevist, Bayer Healthcare Pharmaceuticals, Wayne, NJ), a second acquisition (90° excitation, TR = 10 s, N = 100) was performed to estimate the signal intensity at thermal equilibrium. This estimation assumed a single T1 for the longitudinal decay and that the loss of polarization that occurred during the dissolution process did not change appreciably since performing the calibration measurements.