Rinard George A, Quine Richard W, Biller Joshua R, Eaton Gareth R
Department of Electrical Engineering, University of Denver.
Concepts Magn Reson Part B Magn Reson Eng. 2010 Apr 9;37B(2):86-91. doi: 10.1002/cmr.b.20161.
A crossed-loop (orthogonal mode) resonator (CLR) was constructed of fine wire to achieve design goals for rapid scan in vivo EPR imaging at VHF frequencies (in practice, near 250 MHz). This application requires the resonator to have a very open design to facilitate access to the animal for physiological support during the image acquisition. The rapid scan experiment uses large amplitude magnetic field scans, and sufficiently large resonator and detection bandwidths to record the rapidly-changing signal response. Rapid-scan EPR is sensitive to RF/microwave source noise and to baseline changes that are coherent with the field scan. The sensitivity to source noise is a primary incentive for using a CLR to isolate the detected signal from the RF source noise. Isolation from source noise of 44 and 47 dB was achieved in two resonator designs. Prior results showed that eddy currents contribute to background problems in rapid scan EPR, so the CLR design had to minimize conducting metal components. Using fine (AWG 38) wire for the resonators decreased eddy currents and lowered the resonator Q, thus providing larger resonator bandwidth. Mechanical resonances at specific scan frequencies are a major contributor to rapid scan backgrounds.
交叉环（正交模式）谐振器（CLR）由细导线制成，以实现甚高频（实际上接近250MHz）下体内EPR成像快速扫描的设计目标。该应用要求谐振器具有非常开放的设计，以便在图像采集过程中便于对动物进行生理支持。快速扫描实验使用大幅度磁场扫描，以及足够大的谐振器和检测带宽来记录快速变化的信号响应。快速扫描EPR对射频/微波源噪声以及与场扫描相干的基线变化敏感。对源噪声的敏感性是使用CLR将检测信号与射频源噪声隔离的主要动机。在两种谐振器设计中实现了44dB和47dB的源噪声隔离。先前的结果表明，涡流会导致快速扫描EPR中的背景问题，因此CLR设计必须尽量减少导电金属部件。使用细（AWG 38）导线制作谐振器可降低涡流并降低谐振器Q值，从而提供更大的谐振器带宽。特定扫描频率下的机械共振是快速扫描背景的主要贡献因素。
