Wearable Resonator for In-Vivo Electron Paramagnetic Resonance Tooth Dosimetry

doi:10.21203/rs.3.rs-6256502/v1

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Wearable Resonator for In-Vivo Electron Paramagnetic Resonance Tooth Dosimetry

https://doi.org/10.21203/rs.3.rs-6256502/v1

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published 08 May, 2025

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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-vivomotion. This combination of the wearable resonator and ACC effectively established a motion compensation system for in-vivo EPR tooth dosimetry.

Wearable resonator

in-vivo electron paramagnetic resonance

automatic control

radiation tooth dosimetry

Efficient medical response in large-scale radiation accidents, such as those at Fukushima and Chernobyl, requires a robust field triage system, particularly due to the potential exposure of large populations to radiation [1–3]. Accurate initial assessment of acute radiation syndrome (ARS) heavily relies on estimating absorbed doses quickly, especially those exceeding 2 Gy [4–6]. Various retrospective dosimetry methods have been explored for this purpose, particularly those applicable to the general public who lack personal dosimeters [7–11]. Among these methods, electron paramagnetic resonance (EPR) spectroscopy stands out for its ability to detect radiation-induced free radicals in tooth enamel [12–16]. A key advantage of this method is the stability of the tooth radiation-induced signal (RIS), which can persist for up to 1,000,000 years [12]. The in-vivo EPR spectrometry for tooth dosimetry is well-suited for triage systems due to its rapid measurement capabilities, minimal preprocessing requirements, and ability to distinguish teeth exposed to radiation exceeding 2 Gy [17–19].

During in-vivo EPR tooth dosimetry, patient movement and breathing can distort the EPR spectrum and prolong measurement times [20–22]. Because, the resonator coil is sensitive to any movement of the upper central incisor, which disrupts its impedance-matching state. Previous studies have tackled this issue by introducing electronically controlled tunable resonators equipped with automatic tuning and matching control circuits [23, 24]. These systems maintain impedance matching dynamically, thereby minimizing the loss of EPR spectra due to impedance mismatching and enhancing the signal-to-noise ratio (SNR) for the same measurement duration.

Maintaining consistent calibration settings is essential for applications that measure EPR signal amplitude, such as melanoma diagnosis and tooth dosimetry. Movement-induced changes in the magnetic field energy can affect the EPR signal intensity [21, 25]. Research on the uncertainty in in-vivo EPR tooth dosimetry has shown that total tooth movement within 0.5 mm, including tilting, can result in an uncertainty of ~ 9.1% [26]. Given the likelihood of further movement in real in-vivo situations, addressing this issue is crucial. Previously reported studies have explored solutions such as the application of spring-loaded resonators to prevent tooth slippage and wireless resonators to maintain constant EPR intensity despite subject movement [25, 27, 28]. These methods, while promising, present certain challenges, including the need for improved compensation for lateral displacement on the tooth surface and improved power efficiency of the resonator system.

Wearable devices have attracted attention in biomedical research and healthcare for their user-friendliness and enhanced data acquisition accuracy [29]. The development of such devices often involves the use of flexible substrate materials and conductive patterns customized for human application. In magnetic resonance (MR) fields, patient comfort and overall sensitivity have been improved by using flexible receive coils that are specifically designed to be positioned very near or in direct contact with the subject’s body. However, flexible devices typically exhibit reduced SNR compared to rigid devices, necessitating additional optimization of the circuit design to compensate for performance losses [30, 31]. Furthermore, the performance reliability of wearable devices must be confirmed because the flexible components are used on the live subjects [30]. The perturbation of wearable devices due to human motion has been addressed by implementing an automatic tuning system for enhanced reproducibility [31].

In this study, we designed and fabricated a wearable resonator tailored for in-vivo tooth dosimetry, aiming to minimize the loss and uncertainty of the RIS amplitude and reduce the need for manual intervention in resetting the device due to in-vivo motion. The wearable resonator includes an attachable surface coil, a flexible transmission line, and a coupling circuit. Using ANSYS high-frequency simulation software (HFSS), we optimized the dimensions of the attachable surface coil to maximize the RIS amplitude of a human upper central incisor. The flexible transmission line ensured continuous connectivity between the attachable surface coil and the coupling circuit, even when the tooth shifted position relative to the resonator [32]. We compared the RIS amplitude of the developed wearable resonator with that of a previously reported rigid resonator when measuring the RIS of a tooth sample irradiated with 50 Gy. Additionally, we measured EPR signals while varying the position of the tooth along the central axis of the resonator. Finally, we assessed the stability and user-friendliness of the wearable resonator in an in-vivo setting involving a volunteer.

2.1. Design and configuration of the wearable resonator

A wearable resonator on a tooth was designed for in-vivo EPR spectroscopy in conjunction with a microwave circuit. Figure 1 shows the conceptual design of the wearable resonator applied to a human head phantom. The wearable resonator consists of three components: an attachable surface coil, a flexible transmission line, and a coupling circuit. Each component is tailored to meet specific requirements for effective in-vivo tooth dosimetry. The attachable surface coil serves the crucial function of generating a magnetic field to excite an EPR signal within the subject. It is designed to adhere securely to the tooth surface using adhesive, ensuring consistent positioning with the tooth despite potential movement by the subject. This flexibility is essential to maximize adhesion on the irregular surface of the tooth. Despite the potential movement of the attachable surface coil with the tooth, the opposite end of the coil’s transmission line is connected to the coupling circuit. This arrangement necessitates significant flexibility in the transmission line to accommodate varying positions. Additionally, the coupling circuit should feature a wide tunable frequency range to effectively compensate for impedance perturbation caused by subject movement. The proposed resonator is specifically designed with a resonant frequency of 1.15 GHz to align with the specifications of the RF bridge used in this study.

A circuit diagram of the wearable resonator is shown in Fig. 2. To facilitate the use of the feedback system, we adopted a modified version of a design reported previously [22]. The attachable surface coil, acting as a parallel inductance L_P, was custom-made from a flexible printed circuit board (FPCB). The FPCB consisted of a substrate and a copper layer, etched into the form of a surface coil with a thickness of several tens of micrometers. A double-sided medical-grade adhesive (3M™ 1577 Double Coated Medical Tape) was employed to attach the FPCB-based surface coil to the tooth surface. This adhesive exhibits strong bonding strength while also being readily detachable without causing damage when moderate force is applied. To achieve parallel LC resonance with the surface coil and minimize dielectric loss, a copper-laminated dielectric substrate was cut into 3 mm × 3 mm pieces (Cuflon CF-A-3–7–7, Polyflon Company, Norwalk, CT, USA). A commercial flexible coaxial cable was cut to a length five times the quarter wavelength to serve as parallel transmission lines (225 mm), providing sufficient length to accommodate a wider range of subject movement (SLC-6FT-SMSM+, Mini-Circuits, Brooklyn, NY, USA). A reduction in the coaxial cable length, specifically to either one or three quarter-wavelengths, can result in decreased the transmitted signal attenuation. However, this modification concurrently constrains the permissible range of tooth displacement. The coupling circuit part consists of variable capacitors, C_T and C_M (PTIC, TCP-5082, ON Semiconductor, Phoenix, USA), connected in series and parallel, respectively. This section is connected to the EPR bridge as shown in Fig. 2. To apply bias voltages V_T and V_M for adjusting the variable capacitance, RC low-pass filters were used. An RF choke, implemented using a commercial inductor (100 nH, LQW2BASR10J00L, Murata, Kyoto, Japan), served as a low-pass filter to eliminate microwave frequencies under 1 GHz. The bias voltages V_T and V_M of the coupling circuit part were controlled by an automatic control circuit (ACC), maintaining the critical coupling state of the resonator to minimize reflected RF power [22]. All components were soldered using 3% silver-based solder. The coupling circuit part was shielded with a 6-mm-thick copper case to minimize the effect of the modulation magnetic field, which has a frequency of 21.6 kHz.

To evaluate the resonator characteristics, we used a network analyzer (E5061B, Keysight Technologies, USA) to measure the scattering matrix parameter S₁₁. Measurements were recorded at 1601 data points over a span of 50 MHz. From these measurements, we estimated the resonance frequency and bandwidth of the resonator. The quality factor, which is proportional to the EPR sensitivity of the resonator, was calculated by dividing the resonance frequency by the bandwidth. Additionally, we quantified the shift in resonance frequency resulting from tooth movement.

2.2. Simulation of the attachable surface coil

The attachable surface coil L_P and parallel capacitor C_P, as shown in Fig. 2, are analyzed by finite element method in ANSYS HFSS. In simulation model, critical coupling of the resonator was achieved by fine-tuning C_T and C_M, which are the tuning and matching capacitances, respectively, within the range from 2 to 8 pF. Sinusoidal power was applied to the resonator through a 50 Ω impedance microwave port. The S₁₁ was calculated using linear network analysis across a frequency sweep range of 0 to 3 GHz to estimate the resonance frequency of the resonator. Finally, the dimensions of the attachable surface coil L_P and parallel capacitor C_P were optimized to achieve a resonance frequency close to 1.15 GHz for the wearable resonator.

Figure 3 illustrates an incisor tooth with the attachable surface coil configured in ANSYS HFSS. The tooth model was obtained using a micro-CT image of an extracted central upper incisor (Skyscan 1275, Bruker SkyScan, Kontich, Belgium). Enamel, dentin, and pulp of the tooth were segmented based on the Hounsfield unit obtained from the micro-CT scan. The electrical properties of each material were based on characteristics reported in a previous study [33]. Out of 12 micro-CT-based 3D models of the upper central incisor, the simulation utilized the sample closest to the average size. The plateau region of the enamel surface area on the 3D incisor model measured 5.5 mm in width and 9.5 mm in height; these dimensions are suitable for coverage by the FPCB without significant deformation. To accommodate the curvature of the enamel surface, the FPCB was bent and adhered accordingly. For the design optimization of the FPCB, finite element analysis was conducted within feasible ranges of design parameters for FPCB fabrication. The inner diameter and trace width were varied from 4 to 6 mm and 0.4 to 2 mm, respectively, to maximize the efficiency of magnetic field generation in terms of filling factor (η). The filling factor, a crucial optimization metric for resonators discussed in previous literature on instrumental EPR [34], was calculated within the software based on the following definition:

$$\:\text{f}\text{i}\text{l}\text{l}\text{i}\text{n}\text{g}\:\text{f}\text{a}\text{c}\text{t}\text{o}\text{r},\:{\eta\:}=\frac{{\int\:}_{enamel}^{\:}{B}_{1,\perp\:}^{2}dV}{{\int\:}_{all\:objects}^{\:}{B}_{1}^{2}dV},$$

where $\:{B}_{1}$ denotes the magnetic field generated by the resonator. $\:{B}_{1,\perp\:}$ denotes the component of B₁ orthogonal to an external static magnetic field B₀ (horizontal axis in Fig. 3) and is crucial for EPR signal intensity. Essentially, the filling factor quantifies the ratio of the magnetic field concentrated within the enamel volume to the total magnetic field generated.

2.3. Ex-vivo EPR measurements of the wearable resonator

To evaluate the performance of the fabricated wearable resonator, experimental validation was conducted using an EPR spectrometer interfaced with an inhouse-developed EPR spectrometer [22, 35, 36]. The wearable resonator received tuning and matching voltages (V_T and V_M, respectively) through a previously developed ACC. A microwave power of 100 mW was applied from a signal generation in EPR bridge, with amplitude modulation of the magnetic field intensity set at 0.4 mT for field modulation. The EPR spectrum was obtained and averaged over 30 s, comprising 10 repetitions of a 3-s sweep. For tooth radiation dosimetry, a single extracted tooth sample irradiated with 50 Gy using 220 kVp X-ray, calibrated according to the dosimetric protocol of the American Association of Physicists in Medicine [37], was used. The study was approved by the Institutional Review Board (IRB) of Seoul National University Hospital (Approval No. 2206/027-1330). During EPR measurement, the surface coil of the wearable resonator was attached to the tooth enamel. The coil was positioned such that its axis coincided with the center of the tooth’s horizontal axis, and its inner side aligned with the edge of the tooth enamel, as shown in Fig. 3. For reference, a 1 mM 15N-substituted perdeuterated 2,2,6,6-tetramethyl-4-oxopi peridine-1-oxyl sample (¹⁵N-PDT, CDN Isotopes, Quebec, Canada) sealed in a Teflon tube was simultaneously attached to the surface coil for measurement. The acquired EPR spectrum was analyzed using a home-built EPR signal processing software [36]. The RIS intensity was evaluated based on peak-to-peak amplitude after non-linear fitting the EPR line shape. The RIS amplitudes of the wearable resonator and a conventional rigid resonator [22] were compared.

To assess the impact of tooth displacement, an experimental setup was employed to manipulate the resonator position. Previous work has identified that the tooth displacement along the central axis of the resonator coil, moving away from the tooth’s frontal surface, is the primary determinant of RIS amplitude [7]. In this investigation, the tooth’s position remained constant while the resonator was displaced along the central axis from 0 to 2 mm in intervals of 0.5 mm using a precision moving stage. At each displacement, five EPR spectra were measured using both the rigid and wearable resonators.

An additional experiment was performed to verify the uncertainty and reproducibility of the wearable resonator. To assess the positioning uncertainty of both the resonator and reference sample tube, repetitive measurements were conducted on the irradiated tooth. After acquiring five spectra, the surface coil and sample tube were detached from the tooth and repositioned for another measurement. A total of 30 independent EPR measurements were conducted, and in each measurement, five EPR spectra were acquired for quantitative analysis.

2.4. In-vivo EPR measurements of the wearable resonator

To validate the developed wearable resonator in an in-vivo setting, a single volunteer, who is not irradiated by ionizing radiation, underwent EPR measurements. The EPR spectrum was acquired with and without the ACC. The SNR ratio was determined by dividing the signal amplitude by twice the standard deviation of the noise level. The study was approved by the IRB of Seoul National University (Approval No. 2207/002–002). Figure 4 illustrates the procedural steps for applying the wearable resonator to the subject’s tooth. Initially, the subject’s chin was placed on a chin rest integrated into the magnet system, and the subject’s head was secured using a head restraint to ensure immobilization. The attachable surface coil of the wearable resonator was then affixed to the surface of the subject’s upper central incisor. To identify RIS center in EPR spectrum, a reference sample tube should be measured simultaneously. Before analyzing the EPR spectrum, the reference sample tube was placed over the surface coil on the subject’s tooth and wrapped around the upper dentition with surgical tape, as shown in Fig. 4 (d).

3.1 Characteristics of the developed resonator

Figure 5 (a) presents the magnetic field distribution generated by the wearable resonator within the enamel structure of a 3D tooth model. The $\:{B}_{1,\perp\:}$ magnetic field was generated and concentrated on the enamel volume. The magnetic field was concentrated predominantly within the enamel surface volume encompassing the interior and superior regions of the attachable surface coil. Figure 5 (b) shows the HFSS simulation results depicting the filling factor within the enamel volume as a function of the inner diameter and trace width of the attachable surface coil. Given that the surface enamel width of the incisor model was ~ 5.5 mm, an inner diameter of 5 mm produced an optimal magnetic field distribution for the tooth dimensions. As the inner diameter of the attachable surface coil was reduced below 5 mm, the proportion of the generated magnetic field energy contributing to the enamel volume diminished, relative to the total field energy produced by the coil. Narrower trace widths concentrated magnetic field energy more effectively within the coil, whereas trace widths exceeding 0.7 mm resulted in magnetic field energy leakage beyond the enamel volume. An inner diameter of 5 mm and a trace width of 0.7 mm yielded the maximum filling factor for the attachable surface coil. Based on the HFSS simulation results, the wearable resonator was configured with an optimal filling factor for the attachable surface coil. This approach is expected to maximize the RIS amplitude from an irradiated tooth within the constraints of the tunable resonator design.

3.2 Validation of the wearable resonator

Network analyzer measurements of the scattering matrix parameter S₁₁ confirmed that the configured wearable resonator achieved critical coupling near 1.15 GHz, which is suitable for L-band EPR spectroscopy. The quality factor of the wearable resonator was ~ 63.6, which is 25.9% lower than the Q value of 85.8 measured for a previously reported rigid resonator [22]. This decrease in quality factor is attributed to the reduced thickness of the surface coil and transmission line. These components were designed to be as thin as possible to enhance flexibility while maintaining the same circuit design. Since the quality factor is directly proportional to the EPR signal intensity, this reduction necessitates further optimization. A critical future challenge lies in finding and incorporating advanced coaxial cables that feature higher gauge while preserving mechanical flexibility. This enhancement improves the EPR sensitivity of the wearable resonator, thereby increasing EPR signal intensity without compromising flexibility.

Figure 6 displays the EPR spectrum of 50 Gy irradiated tooth sample measured for 30 seconds ex-vivo measurement using the wearable resonator. Figure 7 shows the variation in the measured RIS amplitude of both the wearable and rigid resonators as a function of tooth movement along the central axis. For the rigid resonator, tooth displacement increased the distance between the surface coil and tooth, resulting in a decrease in RIS amplitude as the tooth moved away from the coil by using precision moving stage. The RIS amplitude of rigid resonator exhibited a variation of ± 14.9% with a displacement of 0.5 mm along the central axis. This phenomenon constitutes a major source of uncertainty in in-vivo EPR tooth dosimetry, as reported previously [25, 26]. In contrast, the wearable resonator maintained a consistent RIS amplitude because the attachable surface coil remained fully attached to the tooth, even when the resonator moved away. The developed resonator exhibited only ± 2.0% variation in RIS amplitude, even with a 2 mm tooth movement along the central axis. Compared to conventional rigid resonators, the developed wearable resonator is expected to mitigate EPR signal uncertainty arising from tooth displacement during in-vivo EPR tooth dosimetry.

In this study, simulating tooth movement resulted in a relatively large uncertainty the moving stage was controlled manually. The uncertainty in RIS amplitude from EPR measurements using the rigid resonator was estimated to be ~ 2.0%, whereas that measured using the wearable resonator was ~ 1.2%. These results suggest that securely fixing the wearable resonator with the sample enhanced measurement stability in EPR measurements conducted in an external environment, unlike those conducted with a conventional EPR cavity.

In validation experiments for EPR tooth dosimetry, the wearable resonator demonstrated improved performance compared to the conventional rigid resonator. The RIS amplitude of the tooth sample measured 2.46 and 2.27 µV for the wearable and rigid resonators, respectively, representing an 8.4% increase for the wearable design, which is noteworthy despite its reduced quality factor. This suggests that the optimized wearable resonator, with its surface coil fully attached to the tooth, more efficiently transfers the magnetic field energy to the tooth enamel. The EPR signal intensity is proportional to the product of the quality factor and filling factor [26, 35, 38]. The improved concentration of magnetic energy on tooth sample by the optimized surface coil could compensate for the loss in quality factor sufficiently to produce such an increase in RIS amplitude. The wearable resonator is projected to enhance operational practicality compared to their rigid loop counterparts, which have already demonstrated sufficient sensitivity for dental dosimetry in large-scale radiological incidents [22].

The reproducibility of the developed wearable resonator was validated through 30 repetitions of resonator coil attachment and subsequent EPR measurements. No correlation was found between the number of trials and RIS amplitude (R² = 0.002). The relative standard deviation in RIS amplitude for each application of the wearable resonator was 6.3%. The reference sample was highly sensitive to electric fields of the resonator due to its aqueouness, so even a slight uncertainty in positioning the sample could affect the RIS amplitude. Implementing a non-aqueous reference sample with a smaller size is expected to mitigate these sources of uncertainty. The ¹⁵N-PDT signal, utilized as the optimum reference specimen, demonstrated a g-factor in close proximity to, yet distinctly separated from, the RIS within the constraints of the limited sweep magnetic field. A prospective research objective is to synthesize and characterize a stable solid-state sample of the ¹⁵N-PDT compound.

3.3 In-vivo EPR measurement

In the in-vivo EPR measurements, the coupling state of the resonator was regulated by the ACC. The coupling compensation range required for the wearable resonator differed from that of the rigid resonator. In a previous study, the coupling status of the rigid resonator without ACC was altered by the perturbation of the distance between the tooth sample and the surface coil, which is the most sensitive part of the resonator. The shift in resonance frequency of the rigid resonator due to the loading tooth was 1.2 MHz [22]. In contrast, the coupling status of the wearable resonator, being attached to the tooth sample, was not affected by the distance between the surface coil and the tooth. Instead, it was influenced by the bending radius of the flexible transmission line. Tooth movement changed the bending radius of the flexible transmission line, resulting in a resonance frequency shift of the wearable resonator. It was estimated that a tooth movement of 20 mm along the central axis resulted in an ~ 0.56 MHz shift in resonance frequency. This indicates that the developed wearable resonator offers better stability than the previous rigid design.

Figure 8 presents in-vivo EPR spectra acquired from one volunteer using the developed wearable resonator. The spectra in Fig. 8(a) and 8(b) were obtained with the ACC turned off and on, respectively. When the ACC was turned off, the in-vivo EPR spectra exhibited good SNR and baseline stability compared to the distorted EPR spectrum obtained using a rigid resonator [22]. However, the in-vivo EPR spectrum without ACC showed a relatively lower SNR than the spectrum with ACC. It can be estimated that the perturbation of coupling status of resonator from direct tooth movement is more significant than from changed bending radius from tooth movement. But, the EPR spectrum without ACC still displayed some baseline distortion, likely caused by the subject’s motion and breathing. When employing ACC, the SNR of the measured EPR spectrum was 13.72, representing an ~ 37.5% increase than the SNR of 9.98 observed for the EPR spectrum acquired without ACC. Moreover, the EPR spectrum with ACC on displayed a flatter baseline than with ACC off, meaning that if the measured tooth is irradiated sample, the RIS from the tooth will be well measured. This result indicated that the ACC was well compensating the perturbed coupling status due to the changed bending radius of the coaxial cable from the tooth movement.

The developed wearable resonator demonstrated superior usability than the rigid resonator for in-vivo EPR tooth dosimetry. Attachment of the wearable resonator eliminated the need for manual intervention to reapply the EPR resonator in response to subject movement. Moreover, the wearable resonator design substantially reduced the mechanical force required for tooth immobilization during in-vivo EPR measurements. The minimization of the applied force contributed to improved subject comfort, facilitating uninterrupted dosimetric data acquisition throughout the measurement protocol. Consequently, we believe that the developed wearable resonator will substantially enhance both the dosimetric accuracy and subject comfort in in-vivo EPR tooth dosimetry.

We developed a wearable resonator to reduce the loss and uncertainty in the RIS amplitude caused by in-vivo motion. The developed wearable resonator remained securely fixed on a tooth, providing an almost constant RIS amplitude even with a displacement of up to 2 mm along the central axis. Additionally, the stable attachment of the wearable resonator reduced the uncertainty in the RIS amplitude to 1.2%. The wearable resonator mitigated signal variability caused by tooth displacement and angulation. Furthermore, the RIS amplitude of the wearable resonator increased by ~ 8.4% compared to the previous rigid resonator. During in-vivo experiments, it was combined with ACC and maintained stable coupling at 1.15 GHz. Thus, the wearable resonator, combined with ACC, completed the motion compensation system for in-vivo EPR tooth dosimetry. This combination also substantially improved measurement efficiency by minimizing the time required to reset the device due to in-vivo motion. We believe that the use of the motion compensation system will significantly enhance the overall performance of in-vivo EPR tooth dosimetry.

Author Contribution

All authors wrote the main manuscript and contributed to the proofreading.C. U. Koo prepared most of figures and pratically measurements.All authors were involved in developing wearable device.Sung-Joon Ye supervised this project and is a recipient of the grants.

Acknowledgments

This research was supported by the Research Program through the Korea Foundation Of Nuclear Safety (KoFONS) using the financial resource granted by the Nuclear Safety and Security Commission (NSSC) of the Republic of Korea. (No. 2003021) and Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2022R1A6A1A03063039).

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Wearable Resonator for In-Vivo Electron Paramagnetic Resonance Tooth Dosimetry

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