Wearable Resonator for In-Vivo Electron Paramagnetic Resonance Tooth Dosimetry

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. Additionally, 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.