Development of Electron Paramagnetic Resonance Magnet System for In Vivo Tooth Dosimetry

Abstract

As part of a homebuilt continuous wave electron paramagnetic resonance (EPR) spectrometer operating at 1.2 GHz, a magnet system for in vivo tooth dosimetry was developed. The magnet was designed by adopting NdFeB permanent magnet (PM) for the main magnetic field generation. For each pole of the magnet, 32 cylindrical PMs were arranged in 2 axially aligned ring arrays. The pole gap was 18 cm, which was wide enough for a human head breadth. The measured magnetic field was compared with the magnetic field distribution calculated in a finite element method (FEM) simulation. EPR spectra of intact human teeth irradiated 5 and 30 Gy were measured for the performance test with the developed magnet system and spectrometer. The measured mean magnetic flux density was estimated to be 44.45 mT with homogeneity of 1,600 ppm in a 2 cm diameter of the spherical volume of the XY plane, which was comparable to the FEM simulation results. The sweep coefficient of the magnetic field sweep coil was 0.35 mT per Ampere in both the measurement and FEM simulation. With ±9 A current, the sweep range was 5.7 mT, which was sufficiently wide to measure the tooth radiation-induced signal (RIS) and reference material. The peak-to-peak amplitude of the measured modulation field was 0.38 mT at the center of the magnet. With the developed magnet fully integrated into an EPR system, the EPR spectra of 5 and 30 Gy irradiated teeth were successfully acquired. The developed magnet system showed sufficiently acceptable performance in terms of magnetic flux density and homogeneity. The EPR spectrum of tooth RIS could be measured ex vivo. The RIS of 5 and 30 Gy irradiated teeth was clearly distinguishable from intact human teeth.

Enhanced Dosimetric Accuracy Using Quality Factor Compensation Method for In Vivo Electron Paramagnetic Resonance Tooth Dosimetry

“…A 1.15 GHz continuous wave EPR spectrometer developed in previous studies was used for the EPR measurements (Park et al 2021; Choi et al 2022). The EPR dose-response data were collected from the teeth with and without the pseudo-in-vivo phantom.…”

“…It can measure and assess one subject in a few minutes with high throughput, and it is relatively easily operated by less skilled operators. Furthermore, in several previous studies, in vivo EPR devices had been developed in light and compact forms so that they can be directly carried with a vehicle to the location of the counter-accident (Williams et al 2011a; Choi et al 2022). Moreover, in vivo EPR tooth dosimetry is a unique technique to measure human subjects noninvasively.…”

Electron Paramagnetic Resonance (EPR) Biodosimetry with Human Teeth: A Crucial Technique for Acute and Chronic Exposure Assessment

“…The study found that the UV-generated EPR signal was minimal compared to doses relevant for triage, with a lifetime effect of 0.33 Gy (a lifetime of 50 y of exposure of these teeth), well below the 2.0 Gy threshold for triage. Choi et al (2022) developed a magnet system for in vivo tooth dosimetry, operating at 1.2 GHz, as part of a homebuilt continuous wave (CW) EPR spectrometer. The magnet, employing NdFeB permanent magnets, demonstrated a wide pole gap suitable for a human head.…”