The Potential of Pulsed Electron Spin Resonance for Tooth-Based Retrospective Biodosimetry

Large-scale triage after major radiological events, such as nuclear reactor accidents, requires a method of ionizing radiation dose estimation called retrospective biodosimetry (RBD) to detect doses in the range of 0.5–8 Gy. A well-known technique for performing RBD is electron spin resonance (ESR), which can be used to measure radiation-induced paramagnetic defects in the enamel of the teeth. The concentration of these defects is linearly correlated with radiation doses in the applicable range. Despite its great potential and proven results when applied to extracted teeth, ESR still struggles to provide accurate in vivo readings. This is mainly because all available ESR-based RBD methods rely on quantitative signals for calculating the concentration of paramagnetic defects in tooth enamel to evaluate the dose. This requires an accurate knowledge of the volume of the measured enamel, which is very difficult to achieve in live subjects (since teeth also include dentin and possibly cavities). Here, we examine radiation-induced paramagnetic defects in the enamel layer of human teeth using advanced pulsed ESR methods, with the ultimate goal of supporting the development of an innovative practical RBD device for in vivo use. We employ a variety of pulsed ESR techniques, such as ESR measurements of spin–spin relaxation time (T2), ESR monitoring of instantaneous diffusion decay time (TID), and dipolar ESR spectroscopy, to explore their possible use to quantify the irradiation dose. Moreover, we develop a special resonator for teeth measurements that make use of such pulse techniques to overcome the constrains of small signal magnitudes and short coherence times. Our results show a good correlation between measured values of T2, TID, and the irradiated dose, but further work is required to improve the robustness, accuracy, and sensitivity of the methods presented before they could possibly be applied for in vivo measurements in typical doses of ~ 2–8 Gy. These findings and approaches may be used in the future for the development of a RBD device to evaluate ionizing radiation doses without prior knowledge of the measured enamel volume.