Magnetic resonance imaging (MRI) is a widely used and accepted method of imaging in the medical community. However, this method can struggle with inherently low sensitivity and lack of differentiation between the target species and background signal, which results in a lack of contrast especially when looking at flow and perfusion imaging. Dynamic nuclear polarization (DNP), while not necessarily a new method, has only recently been applied to MRI. This method increases the MRI contrast by enhancing the MRI ‘signal’ of water outside of the imaging location and then transferring this enhanced signal to the MR imaging location. In the case of DNP, water comes in contact with radicals, and the much greater nuclear spin polarization of the unpaired electron is transferred to <sup>1</sup>H nuclei upon application of electromagnetic radiation of a specific frequency. For flow imaging, the radicals are immobilized on solid supports and held outside the imaging location; enhanced water flows through the beads, through a filter, and then into the MR image. Presently, at a magnetic field of 6.5 mT, we have characterized different polystyrene resins to test their DNP performance for this application. Specifically, we attached 3-carboxy-PROXYL (3-(carboxy)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy free radical) to Tentagel resin through a dehydration mechanism. This resin-radical compound, at about 16 mM, was found to have a 2-4 times better enhancement than any other resin-radical combination tested before. When preliminary flow imaging was tested using a 6.5 mT MRI, five-fold enhanced signal was visible in the images with Overhauser DNP. The increased levels of enhancement provided by this new immobilized radical compound will enable the further development of DNP-enhanced flow imaging at low magnetic fields.

Immobilizing radicals for dynamic nuclear polarization-enhanced magnetic resonance

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.