Optimization of 13C dynamic nuclear polarization at 5 Tesla

Dissolution dynamic nuclear polarization (DNP) is a physics-based technique that amplifies the magnetic resonance spectroscopy (MRS) and imaging (MRI) signals by several thousand-fold. In this work, we have investigated two optimization methods for preparing $^{13}$C DNP samples (glassing matrix deuteration and Gd$^{3+}$ doping) at B = 5 T. Normally, these optimization methods work favorably at W-band field or 3.35 T. At 5 T, deuteration of the glassing matrix still results in an improvement of the $^{13}$C DNP when 4-oxo-TEMPO free radical is used. This effect can be attributed to the lower heat load of the deuterons than protons. An addition of trace amount of Gd$^{3+}$ is still relatively beneficial in enhancing the polarization when trityl OX063 free radical is used, albeit with a less pronounced improvement compared to the results at B = 3.35 T. This suggests that the signal enhancement due to the addition of Gd$^{3+}$ can become saturated at high field. These results will be discussed using a thermodynamic model of DNP.