L-band surface-coil resonator with voltage-control impedance-matching for EPR tooth dosimetry

A surface-coil resonator that is capable of voltage-control for impedance-matching is described in the context of its application in electron paramagnetic resonance (EPR)-based tooth dosimetry. Varactor-based coupling of an 1,150 MHz surface-coil resonator was achieved to supply RF power. The developed resonator consists of a single-turn loop, 9 mm in mean diameter; a capacitor made of a polytetrafluoroethylene (PTFE) substrate; a quarter-wavelength parallel transmission line; a half-wave line balun, and varactors. The surface coil and the PTFE substrate capacitor were connected to a quarter-wavelength parallel transmission line. For the newly developed resonator, an RF magnetic field-generation efficiency of 130 T/W1/2 was achieved, and the sensitivity of the surface-coil resonator was investigated with an irradiated tooth. Measurements consisting of six sets of EPR spectra on a 10 Gy irradiated tooth using this newly developed resonator achieved a standard error of the mean (SEM) of 1.1 Gy. This level of accuracy of dose measurements was comparable to the SEM with a previously developed resonator; however, the previous resonator was not capable of voltage-control for impedance-matching adjustment, which represents a significant advance in facilitating automation. (c) 2013 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 43B:3240, 2013