Wearable Resonator for In Vivo Electron Paramagnetic Resonance Tooth Dosimetry

Abstract

Tooth radiation dosimetry using an in vivo electron paramagnetic resonance (EPR) spectrometer serves as a triage method for victims in large-scale radiation emergencies, such as the Fukushima and Chernobyl accidents. However, the victim’s breathing and movement during in vivo measurements causes signal loss and uncertainty in the radiation-induced signal (RIS). This study aims to address these issues by developing a wearable resonator for a tooth. Using ANSYS High Frequency Structure Simulation (HFSS), the dimensions and configuration of an attachable surface coil were optimized by calculating the magnetic field distribution in the enamel volume of a 3D incisor model. The magnetic energy concentration on the tooth enamel was maximized by the attachable surface coil, which had a 5 mm inner diameter and a 0.7 mm trace width at a given microwave power. To assess the dosimetric performance, a 50-Gy irradiated tooth was measured by an optimized wearable resonator. The tooth measurement was conducted by employing homebuilt 1.15 GHz continuous-wave EPR spectroscopy. The configured wearable resonator produced a constant RIS amplitude with a ± 2.0% variation from an exposed tooth sample, even with a 2 mm movement along the central axis. In addition, secure fixation of the wearable resonator resulted in significant stability, showing a relatively low uncertainty of 1.2% in the RIS amplitude. The wearable resonator also achieved an ~ 8.4% increase in RIS amplitude by concentrating more magnetic energy on the tooth sample compared to a conventional rigid resonator. This enhancement improved the accuracy and sensitivity of in vivo tooth dosimetry. In conjunction with an automatic control circuit (ACC), the wearable resonator acquired undistorted in vivo EPR spectra; thereby, significantly reducing the need for manual intervention to reset the device due to the in vivo motion. This combination of the wearable resonator and ACC effectively established a motion compensation system for in vivo EPR tooth dosimetry.