Resonator for Co-registration EPR/NMR Imaging and Spectroscopy

Introduction Co-registration EPR/NMR imaging has recently attracted more attention as a promising technique [1,3]. In the past, making double EPR/NMR images required two distinct and separated resonators which complicated the setup [1]. Also, modality switching necessitated additional time for tuning and coupling. We developed a double frequency resonator for co-registration EPR/NMR application of in vivo imaging of isolated rat heart. The two different frequencies require two different matching circuits. To accommodate the different matching requirements, we used a special two gap resonator design with two quarter wave connection to the gaps. This configuration provides independent feeding to EPR and MRI parts of the resonator. EPR application of the resonator requires shield and modulation coils. To prevent NMR RF interference we made these parts maximally transparent for low NMR frequency. Both matching circuits were electrically coupled. For in vivo EPR spectroscopy and imaging it is necessary to compensate for motional noise [2,3]. We utilized a varactor diode in the ACC and ATC and manual coupling control circuitry for EPR part of the resonator. Performance of the ATC and ACC was adequate to compensate for a beating heart, with an ATC range of 8 MHz and ACC range of 30 dB.