Fluorine electron double resonance imaging for ¹⁹F MRI in low magnetic fields

This work demonstrates the feasibility of generating fluorine NMR images at a very low magnetic field of 0.015 T by making use of the Overhauser enhancement of ¹⁹F NMR signal brought about by a stable, water-soluble, narrow-line paramagnetic contrast agent. The enhancement in the ¹⁹F NMR images depends on the concentration of the single electron contrast agent, the pO₂, and the electron paramagnetic resonance (EPR) irradiation power. The applicability of this technique for ¹⁹F NMR imaging is demonstrated with phantom samples, where a time resolution of 4-10 min is achieved. Proton electron double resonance imaging (PEDRI) and fluorine electron double resonance imaging (FEDRI) images were also obtained from rat kidneys ex vivo, perfused with 10 mM Oxo63 and 10 M trifluoroacetic acid. The spatial and temporal resolutions of these images are comparable to those obtained at magnetic fields 2-3 orders of magnitude larger. Constant NMR frequency (628 kHz) operation permits both FEDRI and PEDRI of identical slices without removing the object under investigation. This feasibility of coregistration of proton-based anatomical PEDRI image with physiological FEDRI image offers good potential for studying fluorine-containing tracers.