M.Sc Thesis

M.Sc StudentSirota Ksenia
SubjectPulsed Electron Spin Resonance Ex-situ Probe for Tooth
DepartmentDepartment of Biomedical Engineering
Supervisors PROF. Haim Azhari
PROF. Aharon Blank
Full Thesis textFull thesis text - English Version


Major nuclear events, such as a nuclear power plant accident or a terrorist use of a nuclear device are all remote but still possible scenarios, for which modern society must be prepared. As a result of such an event, populations may be exposed to doses of ionizing radiation that could cause direct clinical effects within days or weeks. There is a critical need to determine the magnitude of the exposure of individuals by measuring the radiation absorbed dose which is a measure to the amount of energy deposited in a human by ionizing radiation. Having accurate information regarding the absorbed dose would allow providing individuals who are significantly at risk with the appropriate procedures immediately, while those without a significant probability of acute effects could be removed from the need for further consideration in the medical system.

Quantifying the absorbed radiation dose based only on biological material is termed biodosimetry. Electron spin resonance (ESR) is an important spectroscopic technique for the observation of unpaired electron spins in paramagnetic species that can be used for this purpose. In-vivo ESR measurement of radiation induced paramagnetic defects in the enamel of teeth are currently considered to be the most well-established physical biodosimetry method.

All ESR instruments require applying a combination of homogenous static magnetic field and microwave power to the measured sample. The current state of the art of in vivo ESR tooth dosimetry involves the use of relatively large and expensive electromagnets combined with resonant excitation/detection coils that are a few cm in size measuring a whole tooth. These systems are not suitable for providing diagnosis to large populations in a catastrophic event.

A unique and compact ESR probe that includes a static field source and a microwave resonator for the measurements of paramagnetic defects in the tooth enamel is presented. The probe can measure the tooth when it is positioned just above its outer surface, i.e. in “ex-situ” geometry. It is operated in pulsed mode at a frequency of ~ 6.2 GHz that corresponds to the magnitude of the static magnetic field of its permanent magnets. A detailed design of the probe is presented, along with its specifications and experimental results that verify its sensitivity and capability to measure gamma-irradiated teeth. This probe could be used in the future as a simple, affordable, compact and transportable mean for quick and reliable biodosimetry.