Despite the great importance of MRI in the medical field today, it still can suffer from low sensitivity and lack of contrast between the target species and background signal. This research investigates a technique called dynamic nuclear polarization (DNP) which involves the transfer of polarization from free radical electrons to hydrogen-1 nuclei, hyperpolarizing the MRI signal of water. This allows for the tracking of DNP-enhanced water against unenhanced background signal, giving unique contrast without the addition of any external contrast agent. Here, we investigate DNP in an ultra-low field MRI operating at 6.5 mT, with an eye towards enhancing the information available from this low-cost and accessible MRI system. One of the innovations in the development of DNP-enhanced MRI was the immobilization of the radical species onto small beads, so that water could flow over the beads during the DNP process and then be separated from the beads by a filter, thus producing radical-free DNP-enhanced water. To increase signal enhancement, polyelectrolytes were used as linker arms between the radicals and beads to increase the radical concentration and water accessibility of the radicals, specifically polyvinylimidazole (PVIm), polyethylenimine (PEI), and Pectin. A non-polymer-based immobilized radical, where the radical is directly bound to the bead, is tested to compare with the polymer-based immobilized radicals. Results indicate the radical directly bound to the beads with a radical concentration of about 8-9 mM had higher DNP signal enhancement at 6.5 mT than any of the polymer-based immobilized radicals. DNP-enhanced MRI with the best immobilized radicals produced only modest MRI signal enhancements of -1.3 fold.

Investigating polymer-based immobilized radicals using dynamic nuclear polarization-enhanced MRI

251st National Meeting (2016)

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