Fig. 2.

(a) A simulation for hyperpolarized ¹³C urea shows how a short total diffusion measurement time relative to the T₁ makes calculations of the diffusion coefficient less sensitive to the apparent T₁ accuracy. The white line represents the (total diffusion measurement time)/true T₁ ratio used in our hyperpolarized ¹³C urea experiments, where errors of up to 25% in apparent T₁ only result in less than 5% errors in the diffusion coefficient. (b) Diffusion coefficients of ¹³C urea at 27°C, measured using thermal equilibrium polarization and hyperpolarization. b-value is a measure of the degree of diffusion weighting.