Dissolution DNP using trityl radicals at 7 T fieldElectronic supplementary information (ESI) available. See DOI: 10.1039/c7cp03633g

Dissolution DNP has become an important method to generate highly polarized substrates such as pyruvic acid for in vivo imaging and localized spectroscopy. In a quest to further increase the polarization levels, which is important for in vivo MRI employing 13 C detection, we describe the design and implementation of a new DNP polarizer that is suitable for dissolution operation at 7 T static magnetic field and a temperature of 1.4 K. We describe all important sample preparation steps and experimental details necessary to optimize trityl based samples for use in our polarizer at this higher field. In [1- 13 C]-pyruvic acid polarization levels of about 56% are achieved, compared to typical polarization levels of about 35-45% at a standard field of 3.4 T. At the same time, the polarization build-up time increases significantly from about 670 s at 3.4 T to around 1300-1900 s at 7 T, depending on the trityl derivate used. We also investigate the effect of adding trace amounts of Gd 3+ to the samples. While one trityl compound does not exhibit any benefit, the other profits significantly, boosting achievable polarization by 6%. Characterization of direct 13 C DNP at 1.4 K and 7 T field using trityl radicals.