Electron Spin Relaxation Time Measurements Using Radiofrequency Longitudinally Detected ESR and Application in Oximetry

✍ Scribed by Ioannis Panagiotelis; Ian Nicholson; James M.S. Hutchison

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 198 KB
• Volume: 149
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.2000.2282

✦ Synopsis

Longitudinally detected ESR (LODESR) involves transverse

ESR irradiation with a modulated source and observing oscillations in the spin magnetization parallel to the main magnetic field. In this study, radiofrequency-LODESR was used for oximetry by measuring the relaxation times of the electron. T 1e and T 2e were measured by investigating LODESR signal magnitude as a function of detection frequency. We have also predicted theoretically and verified experimentally the LODESR signal phase dependence on detection frequency and relaxation times. These methods are valid even for inhomogeneous lines provided that T 1e T 2e . We have also developed a new method for measuring T 1e , valid for inhomogeneous spectra, for all values of T 1e and T 2e , based on measuring the spectral area as a function of detection frequency. We have measured T 1e and T 2e for lithium phthalocyanine crystals, for the nitroxide TEMPOL, and for the single line agent Triarylmethyl (TAM). Furthermore, we have collected spectra from aqueous solutions of TEMPOL and TAM at different oxygen concentrations and confirmed that T 1e values are reduced with increased oxygen concentration. We have also measured the spin-lattice electronic relaxation time for degassed aqueous solutions of the same agents at different agent concentrations. T 1e decreases as a function of concentration for TAM while it remains independent of free radical concentration for TEMPOL, a major advantage for oxygen mapping. This method, combined with the ability of LODESR to provide images of exogenous free radicals in vivo, presents an attractive alternative to the conventional transverse ESR linewidth based oximetry methods.