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Rats were given vitamin E (Vit-E), idebenone (ID), or vitamin C (Vit-C) in their food for 2 or 4 weeks. After feeding, the ability of rats to reduce 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol) in terms of the half-life of Tempol was examined as a specific marker. Tempol was repeatedly injected intravenously, and its half-life was serially evaluated by an in vivo electron spin resonance (ESR) technique. The radical-reducing ability in rats was enhanced differently by Vit-E, ID, and Vit-C, i.e., slow onset of the ability after Vit-E and ID (lipid-soluble antioxidants) and fast onset after Vit-C (a water-soluble antioxidant).

The flexible surface-coil-type resonator (FSCR) operating in a 700 MHz microwave electron spin resonance (ESR) system was applied to measure the nitroxide radicals at a specific area in rats. The FSCR was composed of a single-turn coil with a diameter of 5 mm and two flexible coaxial lines of 450 mm in length. For an endoscope-like application, the FSCR was inserted into the rectum of the rat and sequential changes in the ESR signals of the intravenously injected nitroxide radical (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl; TEMPOL or 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy; carbamoyl-PROXYL) were measured. The ESR signal intensity of the nitroxide decreased according to first-order kinetics. For a stethoscope-like application, the FSCR was placed at several sites on the abdominal skin of the rats receiving a subcutaneous injection of carbamoyl-PROXYL, and diffusion and/or metabolism of the radical in the skin was observed.

A rapid field scan L-band electron spin resonance computed tomography (ESR-CT) system has been developed in order to obtain three-dimensional images of the distribution of free radicals in a sample. The ESR system comprises an L-band (ca. 700 MHz) ESR spectrometer, an air-core electromagnet equipped with a field-scanning coil, three field-gradient coils, and a microcomputer.The rapid field scan (15 mT/s) causes a delay in the magnetic-field strength due to eddy-current losses. However, it was found that the magnetic field strength could be corrected by a simple mathematical equation related to a low-pass filter model. Using this system, the original ESR data used to obtain one three-dimensional ESR-CT image could be obtained in 150 s. The time course of the ESR-CT images of the test sample containing the reaction of nitroxide radical with ascorbate ion has been shown as an example of a spatiotemporal measurement.