Development of an EPR imager for the cerebral function analysis

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The goal of this study was the development of an EPR imager for the cerebral function analysis. A key problem of the image reconstruction in EPR imaging was tacked. A systematic selection of filtering function to obtain the optimum image resolution was investigated. The direct Fourier transformation reconstitution(DFTR)method is suitable to understand the effect of the filter characteristics. We paid attention to the signal-to-noise ratio of the spectra to determine the cut-off frequency in the filter function. Although the usefulness of the image reconstruction by this technique should be verified in the imaging of more realistic samples, our fundamental concept was confiemed. The frequency characteristics of the noise can be treated as the white noise. Moreover, the technology using the optical device that enables remote control of the resonant frequency was developed for of the volume coil such as a loop-gap resonator. This realized the tuning circuit with less electromagnetic induction by magnetic field modulation which becomes a problem in the use of a varactor diode. The sensitivity was decreased by using the automatic tuning control, but the stability of the measurements was improved. It is necessary to improve the sensitivity in the future. Although it was a research for a very large goal, namely, the development of the EPR imager for the cerebral function analysis, we solved some technical problems. The systematic approach to selecting the cut-off frequency in image reconstruction and the optical technique to control the resonance frequency are useful for EPR study.