Going Low in a World Going High: The Physiologic Use of Lower Frequency Electron Paramagnetic Resonance
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Applied Magnetic Resonance
REVIEW
Going Low in a World Going High: The Physiologic Use of Lower Frequency Electron Paramagnetic Resonance Howard J. Halpern1,2 · Boris M. Epel1,2 Received: 5 July 2020 / Revised: 20 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Yakov Sergeevich Lebedev was a pioneer in high-frequency EPR, taking advantage of the separation of g-factor anisotropy effects from nuclear hyperfine splitting and the higher-frequency molecular motion sensitivity from higher-frequency measurements (Appl Magn Reson 7: 339–362, 1994). This article celebrates a second EPR subfield in which Prof. Lebedev pioneered, EPR imaging (Chem Phys Lett 99: 301–304, 1983). We celebrate the clinical enhancements that are suggested in this low-frequency work and imaging application to animal physiology at lower-thanstandard EPR frequencies. Abbreviations EPR Electron paramagnetic resonance O2 Molecular oxygen pO2 Partial pressure of dissolved molecular oxygen MHz Megahertz, units of 106 Hz WWII World war two RF Radiofrequency ρ Charge density J Current density σ Material conductivity E Electric field intensity B Magnetic field induction ω Electric and magnetic field temporal angular frequency ν Electric and magnetic field temporal frequency λ Wavelength k Wave number = 2π/λ ε Local material permittivity
* Howard J. Halpern h‑[email protected] 1
Center for EPR Imaging in Vivo Physiology, University of Chicago, Chicago, USA
2
Department of Radiation and Cellular Oncology, University of Chicago, Chicago, USA
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H. J. Halpern, B. M. Epel
μ Local material permeability ESE Electron spin echo SLR Spin lattice relaxation IRESE Inversion recovery electron spin echo, a SLR based but echo detected measurement used in pO2 imaging OX071 Also known as OX063d24, the spin probe capable of quantitative pO2 imaging R1e Longitudinal electron relaxation rate R2e Transverse electron relaxation rate T1e 1/R1e Longitudinal electron relaxation time for signal reduction by 1/e T2e 1/R2e Transverse electron relaxation time for signal reduction by 1/e CW Continuous wave (measurement technique) τ Delay time between (1) the 90° pulse rotating magnetization initially oriented in the direction of the tmain magnetic field to a direction transverse to that direction, allowing regions of higher or lower magnetic field to develop larger or smaller phase delays and (2) the 180° pulse rotating the magnetization about the main magnetic field direction to correct for the local magnetic field inhomogeneities leaving only information from intrinsic transverse relaxation processes. T Delay time between (1) the 180° pulse rotating magnetization initially oriented in the direction of the tmain magnetic field to the opposite direction and (2) the 90° pulse rotating magnetization to a direction transverse to that direction, the beginning of a fixed τ electron spin echo magnetization readout mT Millitesla mT/m Millitesla/meter measure of magnetic field gradient str
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