Three-dimensional electron paramagnetic resonance (EPR) imaging of an X-ray-irradiated bovine tooth: A feasibility study

This study aimed to demonstrate the feasibility of three-dimensional (3D) mapping of an X-ray-irradiated bovine tooth using 750-MHz continuous-wave electron paramagnetic resonance (EPR). A bovine tooth that received 50-Gy X-ray was used as a dosimetry sample. To enhance the sensitivity of EPR detection, we used an ultra-low-noise saturated power amplifier following an RF synthesizer. Moreover, the automatic tuning control (ATC) system, which locks the frequency of the radiofrequency (RF) resonator to the RF carrier frequency, was combined with another RF frequency adjustment system for the RF synthesizer to enable long-term data acquisition over several hours. A 4-hydroxy-TEMPO radical solution was measured as a standard EPR signal source to investigate the enhancement of signal sensitivity. The radiation-induced EPR signals in tooth enamel were reconstructed using the algebraic reconstruction technique (ART). The signal-to-noise ratios achieved for the 4-hydroxy-TEMPO radical solution and a 50-Gy irradiated bovine tooth were twice as high as those obtained previously. Radiation-induced signals in the bovine tooth were mapped in 3D space for 3 h 45 min. The spatial resolution in the 3D map reached 2.1 mm. While low-field EPR was considered to be less sensitive for mapping the absorbed dose of an irradiated tooth, we demonstrated that low-field EPR at 26.8 mT (750 MHz) is applicable to the 3D mapping of 50-Gy-irradiated tooth enamel. Our findings represent a step towards a technology for absorbed-dose mapping of human teeth in cases of accidental exposure to head and neck cancer patients.