Rapid-scan EPR imaging

Authors

Sandra S. Eaton, University of DenverFollow
Yilin Shi, University of Denver
Lukas Woodcock, University of Denver
Laura A. Buchanan, University of Denver
Joseph McPeak, University of Denver
Richard W. Quine, University of DenverFollow
George A. Rinard, University of DenverFollow
Boris Epel, University of Chicago
Howard J. Halpern, University of Chicago
Gareth R. Eaton, University of DenverFollow

Publication Date

7-2017

Document Type

Article

Organizational Units

College of Natual Science and Mathematics, Chemistry and Biochemistry

Keywords

Direct detection, Deconvolution, Imaging, In vivo, Nitroxides

Abstract

In rapid-scan EPR the magnetic field or frequency is repeatedly scanned through the spectrum at rates that are much faster than in conventional continuous wave EPR. The signal is directly-detected with a mixer at the source frequency. Rapid-scan EPR is particularly advantageous when the scan rate through resonance is fast relative to electron spin relaxation rates. In such scans, there may be oscillations on the trailing edge of the spectrum. These oscillations can be removed by mathematical deconvolution to recover the slow-scan absorption spectrum. In cases of inhomogeneous broadening, the oscillations may interfere destructively to the extent that they are not visible. The deconvolution can be used even when it is not required, so spectra can be obtained in which some portions of the spectrum are in the rapid-scan regime and some are not. The technology developed for rapid-scan EPR can be applied generally so long as spectra are obtained in the linear response region. The detection of the full spectrum in each scan, the ability to use higher microwave power without saturation, and the noise filtering inherent in coherent averaging results in substantial improvement in signal-to-noise relative to conventional continuous wave spectroscopy, which is particularly advantageous for low-frequency EPR imaging. This overview describes the principles of rapid-scan EPR and the hardware used to generate the spectra. Examples are provided of its application to imaging of nitroxide radicals, diradicals, and spin-trapped radicals at a Larmor frequency of ca. 250 MHz.

Publication Statement

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Recommended Citation

Eaton, S.S., Shi, Y., Woodcock, L., Buchanan, L. A., McPeak, J., Quine, R. W., . . . Eaton, G. R. (2017). Rapid-scan EPR imaging. Journal of Magnetic Resonance (1997), 280, 140-148. DOI: 10.1016/j.jmr.2017.02.013.