The Methodology Research Of In Vivo Measurement Of Nail Dose By EPR Technique

Nuclear and radiation emergency may cause a large number of people received over radiation dose.It is important to rapidly evaluate dose and screen out over exposed people at accident site for nuclear emergency medical rescue,and it is also an important issue in the radioactive medicine field.Electron Paramagnetic Resonance(EPR)technique can specifically detect the concentration of radiation-induced free radicals in human biological samples such as teeth and nails,and has become an important biological dosimeter for radiation accidents.In addition,EPR technique has the potential feature to achieve early and rapid dose measurement at accident site.Commercial EPR spectrometer is usually used in ex vivo measurement for EPR nail dosimetry.During ex vivo measurements,the nails have to be cut into fragments,and this process generates mechanically-induced signal(MIS)which can seriously interfere radiation-induce signal(RIS),thus affecting the accuracy of dose evaluation and making EPR dosimetry of nail difficult in applications under real sceneries.If the in vivo EPR measurement could be achieved,the generation of MIS could be avoided,which could greatly improve the accuracy and reliability of the EPR dosimetry.This work realized simulated in vivo measurement of intact nails based on self-developed in vivo EPR system,and studied the characteristics of background signal(BKG),mechanically induced signal(MIS)and radiation-induce signal(RIS).The dose evaluation method and individual BKG restoring method of in vivo measurement of nails were preliminarily established.The factors that affect the accuracy of in vivo measurement were discussed,and the corresponding correction methods were proposed.The main contents and results are as follows:1.Performance evaluation of the in vivo EPR spectrometer.The standard DPPH dot sample was used to evaluate the stability of in vivo EPR spectrometer.The stable Mn2+/Ca O was used as the inlay standard sample,which effectively reduced the measurement error caused by system state fluctuation,and improved accuracy of measurement.We established a simulative method of in vivo EPR measurement for intact nails following a standard method for collecting intact nails.The measurement stability of the method was evaluated,that the relative error of 10 repeated measurements is about 6%.2.The characteristics of the EPR signal of nails were studied.The EPR signals in unirradiated nails includes background signal and mechanically induced signal,which are the key factors affecting the accuracy and dose limit of EPR nail dosimetry.In this study,the characteristics of MIS and its relationship with the cutting direction were studied.The MIS intensity was significantly related to cutting directions,which make it difficult to accurately deduct MIS in ex vivo measurements.The distribution feature of BKG and its relationship with storage condition were also studied.The results showed that the background signal of nails had a wide distribution range,and its intensity was affected by the environmental humidity.3.The dosimetric characteristics under in vivo measurement condition were studied.The decay and dose response characteristics of the RIS were studied through intact nails.The results showed that the RIS decay exponentially,and its half-life period was about 4.6 days.It had a linear dose response within dose range of 2-10 Gy.The method of water treatment combined with temperature change was proposed to eliminate the RIS and restore BKG of individual nail,and its feasibility has been verified.4.The actual in vivo EPR nail measurement,and the analysis and correction methods of its interference factors.With the participate of volunteers the actual in vivo measurement was conducted,and the actual in vivo spectrum of background signal was obtained under the condition that the vibration interference in in vivo measurement was reduced by fixing device of finger and arm.The in vivo radiation-induced signal was obtained by method that intact nails were pasted to fingers.Due to the influence of human physiological activities,the signal-to-noise ratio of actual in vivo measurement has decreased,but it can still meet the requirements of dose analysis.The Fourier transform method was used to analyze the characteristics of in vivo EPR spectrum,and the band-stop filter was used to eliminate interference signal of human physiological activity.Considering the fact that nail length of irradiated people may vary differently,the method for correcting the sample volume by image recognition was proposed.These works provided a potential way to eliminate the influencing factors in in vivo measurement.Conclusion: Using the currently established nail EPR dose measurement method,the EPR signal of the nail can be detected under actual in vivo conditions,and this method completely avoids the interference of mechanically induced signal.The water treatment combined with the temperature change method can effectively recover background signal of individual nail sample,thereby RIS intensity can be obtained more objectively and the dose estimation error caused by the individual difference of BKG can be avoided.The preliminary result of this study will improve the reliability and practicality of in vivo dose measurement of nail.The results of this study also show that in vivo dose measurement of nail can be a suitable method for rapid and early dose initial screening after the accident,and provides a reference for further accurate dose diagnose.