Figure 5. The lifetime of the polarization is long at high field.

The decay of one sample of hyperpolarized ¹³C-HEP was monitored by acquiring 12 non-localized spectra with a repetition time of T_R=15 s and a small flip angle of 9° (squares). A mono-exponential decay function (line) was fitted to the data and yielded T₁∼(79±2) s. A correction factor—described in the methods—was applied to each data point to compensate for the fact that each measurement pulse consumes a finite amount of the magnetization. The T₁ determined from the low flip angle measurement correlates well to the polarizations that were detected by full, 90° excitations 0, 20 and 120 s after the HP. For each time point, the mean of three measurements (bars) is shown, and error bars indicate the s.d. The tracer concentration was 5.54 mM in D₂O.