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Detection and imaging of oxygen-centered free radicals with low-frequency electron paramagnetic resonance and signal-enhancing deuterium-containing spin traps

We have identified and imaged oxygen-centered free radicals with low-frequency electron paramagnetic resonance (EPF) spectroscopy and deuterium-containing spin traps to probe the feasibility of spin trapping deep in large (~10 cm), heterogeneous aqueous/hydrophobic (e.g., biologic) systems. Spectra at 250 MHz from spin trapping superoxide and hydroxylradicals in aqueous solutions of deuterated analogs of DMPO (5,5-dimethyl-1-pyrroline-1oxyl) were obtained, and the superoxide measurements were compared with those at X-band. Modification of X-band spectral line positions occurs due to the breakdown of the high-field approximation. Solution of the Breit-Rabi equations governing low-field measurements reproduces most of the observed line position changes. Sensitivity is found to scale with (frequency)N, with N~1.6 largely compensated for by the increase in sample volume. A two0dimensional spectral-spatial image of a phantom filled with heterogeneous concetrations of spin trap and subjected to gamma radiation from 60Co is presented.

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