对辐照牙釉质EPR谱数学模拟的研究

目的　建立辐照牙釉质EPR谱数学模拟方法。方法　采用高斯函数一阶微商作为基本的模型函数 ,编写基于Marquardt Levenberg非线性最小二乘法曲线拟合算法的计算程序模拟辐照牙釉质EPR谱 ,并检验拟合精度。结果　对 2 70和 84 0mGy辐照的牙釉质样品的EPR复合谱 ,拟合后的残谱分别为 - 1 6 1± 2 3 5 9和 - 3 77± 2 4 94 ,残谱均值和标准差分别占各自峰高的 0 3%、3 8%和 0 4 %、3%。结论　这种算法和模型函数能很好地模拟辐照牙釉质EPR复合谱。     

用电子顺磁共振波谱拟合方法估算牙釉质辐射剂量

目的 探讨运用电子顺磁共振(electron paramagnetic resonance, EPR)波谱拟合技术估算牙釉质EPR辐射剂量的准确性。方法 编制多成分叠加型EPR粉末波谱拟合软件,分别拟合牙齿本底信号(background signal,BS)和辐照诱发信号(radiation-induced signal,RS)的EPR波谱模型,用波谱模型叠加计算方法拟合出实际辐照后牙釉质的EPR波谱,从复合谱中提取出RS成分并计算其相对强度,建立剂量响应曲线,估算样品剂量,并将剂量估算结果与传统的波谱强度测量方法进行比较。结果 拟合获得的BS信号为单峰高斯线形粉末谱,g=2.0035,线宽Hpp=0.650-1.100 mT; RS信号为轴对称多晶粉末谱线形,其g_⊥=2.0018,g_‖＝1.9965,线宽Hpp=0.335-0.400 mT;分离BS与RS后得到的RS相对强度与辐照剂量呈线性相关,剂量响应方程为:y=240.74x+76 724(R²=0.9947),剂量估算结果相对误差期望值为0.13。结论 EPR波谱拟合方法在一定程度上提高了牙釉质辐射剂量估计的准确性和可信度。     

ETS对牙釉质EPR谱去卷积程序拟合结果的影响

牙釉质EPR剂量测定方法是通过测量射线在恒牙的釉质中产生的CO2^-自由基浓度，来获取牙釉质累积剂量的。虽然在高剂量的剂量重建中，样品管及微波腔信号（the EPR spectrum of the empty sample tube and the microwave cavity，ETS）的影响常可忽略，但在剂量较低时，这些因素就应当加以考虑。为了明确在低剂量范围ETS对剂量测定的影响程度，笔者通过测量，应用以高斯函数一阶微商数学模型为基础的去卷积程序，对不同剂量水平的样品谱进行拟合，观察ETS对程序结果的影响，并介绍ETS处理方法；同时讨论了该程序存在的其他问题及解决方案。     

嚼烟习俗地区的牙釉质电子自旋共振剂量学的研究

目的 研究嚼烟习俗对牙釉质电子自旋共振(ESR)剂量学的影响。方法 用机械方法获得20个孟买地区的舌侧牙釉质样品与10个混合均匀的日本人舌侧牙釉质样品。用⁶⁰Co γ射线分别照射部分牙釉质样品,使用ESR波谱仪测量辐射前和不同辐射剂量后牙釉质样品的ESR信号。结果 9个孟买牙釉质样品,其ESR的本底信号强度明显高于日本人的平均水平,为日本人水平的1.5~3.3倍。ESR本底信号强度较高的样品,γ射线照射后,剂量学信号的辐射响应略低,说明高本底可能降低了辐射剂量的灵敏度。6个样品辐射响应的平均值为(0.42±0.03)mGy,与日本牙釉质混合样品很相近。结论 嚼烟地区的部分牙釉质的ESR本底水平明显高于一般平均水平,可能是嚼烟中大量的烟碱与牙釉质相互作用的结果。进一步研究特殊生活习俗对牙釉质ESR剂量学的影响,有助于提高不同地区剂量重建的精度,为正确地评价辐射事故剂量提供科学依据。     

牙釉质电子自旋共振剂量学的本底拟合扣除法研究

牙釉质ESR剂量学近年来得到了广泛的应用。然而，牙釉质中含有一定量的有机物，其ESR信号对射线不敏感，称之为本底信号。由于本底信号很宽，基本上覆盖了低剂量范围（约几百mGy）的剂量学信号，而一般情况下的事故剂量大多不超过1Gy，因此如何减少本底的影响，较准确地估算出受照射剂量，一直是ESR剂量学的一个重要课题。目前进行剂量重建的方法主要有附加照射法、部分刻度法和刻度曲线法。其中刻度曲线法由于大大节省了图谱处理时间且对样品没有破坏性而受到广泛关注。但是该方法是基于辐射灵敏度的个体差异很小的这样一个假设。     

荧光原位杂交微核技术在辐射生物剂量学的应用研究

目的探讨荧光原位杂交(FISH)微核作为生物剂量计及评价职业受照射人群辐射效应的可行性。方法用^137Cs7射线不同剂量(0．1～2．5Gy)照射离体人外周血细胞，用泛着丝粒探针的FISH技术进行微核分析，拟合剂量效应方程；检测医用X射线工作者的无着丝粒微核率并估算其生物剂量。结果离体照射条件下微核率随吸收剂量增加而增加，以无着丝粒微核增加为主，着丝粒微核仅有轻度增加。微核率与剂量之间的拟合曲线方程，CB微核法：Y=0．005 0．036D 0．01ID^2，R^2=0．99；FISH微核法：Y=0．001 0．035D 0．007D^2，R^2=0．99。结论FISH微核法优于CB微核法。用FISH微核法对医用X射线工作者的检测结果显示无着丝粒微核率可以用来估算生物剂量。     

牙釉质EPR剂量测定方法的主要影响因素分析

EPR(电子顺磁共振)剂量测定方法是回顾性测定个人辐射剂量的主要方法，它能够准确估算出很久以前发生的辐射照射事件的吸收剂量值，其理论基础是：在牙釉质中，辐射所致自由基水平随着辐射剂量的增加而增加。目前，将EPR方法用于低剂量测定还存在一些困难，为了降低测量阈值，减小误差，优化方法，需要进一步研究该方法的影响因素。本重点分析了影响牙釉质EPR剂量方法测量阈值和测量结果不确定度的主要因素，并对解决这些问题的修正方法讲行了讨论。     

不同制备方法对牙釉质样品ESR信号的影响

目的研究不同制备方法对牙釉质样品ESR信号的影响，有效地提高牙釉质样品ESR剂量学的灵敏度。方法对无放射线照射史成年人臼齿分别用化学、机械以及机械加化学方法进行处理，制备牙釉质样品。利用电子自旋共振仪测定不同制备方法处理的样品在^60Coγ射线照射不同剂量后的ESR信号。比较分析其灵敏度，从而寻求一种对牙釉质样品ESR信号影响较小的样品制备及处理方法。结果不同方法处理的牙釉质样品的ESR信号，对^60Coγ射线的响应有较明显的差异。结论利用牙釉质ESR剂量学重建受照人员剂量时，尤其是使用附加照射法进行较低剂量重建时，选择合适的样品制备方法是十分重要的。     

辐射剂量和机型对瞬时kVp切换单源双能CT物质分离技术肝脏铁与脂肪定量评估的影响

【摘要】目的：探讨辐射剂量、机型对瞬时kVp切换单源双能CT肝脏铁和脂肪沉积定量评估的影响。方法：制作肝脏铁沉积体模（铁浓度分别为50.000、25.000、12.500、6.250、3.125、0mg/mL大鼠肝脏匀浆液）、脂肪沉积体模（脂肪体积百分比分别为100%、60%、30%、10%、0%大鼠肝脏匀浆液）：①应用256-MDCT分别以管电流200、320、485mA扫描体模，管电压80、140kVp瞬时切换，相应CTDIvol分别为4.88，8.21，12.64mGy；②应用64-MDCT扫描体模，管电流为375mA、CTDIvol为12.92mGy。以标准算法分别重建铁（水）、脂肪（水）基物质图像，将图像传至ADW4.6工作站，利用GSI分析软件（GSI Viewer）分析，于体模内每个试管横断面中心放置3个直径为6mm、面积为28.26mm2圆形感兴趣区（ROI），然后记录其平均值为各ROI虚拟铁浓度值（VIC）、虚拟脂肪浓度值（VFC），先对256-MDCT 3组辐射剂量下的VIC、VFC分别进行单因素方差（ANOVA）分析；再分析256-MDCT辐射剂量为12.64mGy下、64-MDCT辐射剂量为12.92mGy下，VIC与肝脏铁浓度（LIC）相关性，VFC与肝实际脂肪浓度(LFC)的相关性。结果：①ANOVA分析显示3组CTDIvol下肝铁沉积模型VIC组间差异P=0.993（F=0.007），组间差异无统计学意义；三组CTDIvol下肝脂肪沉积模型VFC组间差异P=0.976（F=0.024），组间差异无统计学意义；即不同辐射剂量下测得的3组VIC、VFC组间差异均无统计学差异。②256-MDCT组CTDIvol为12.64mGy下与64-MDCT组CTDIvol为12.92mGy下，两组铁沉积模型VIC与LIC均呈高度正相关，相关系数r=0.998（P=0.000），256-MDCT组12.64mGy下拟合铁的线性方程为y=2.179x-2.923(y为LIC，x为VIC，R2=0.996)，64-MDCT组12.92mGy下拟合铁的线性方程为y=2.714x+16.971 (R2=0.996)；两组脂肪沉积模型VFC与LFC均呈高度正相关，相关系数r=1.000（P=0.000）；256-MDCT组12.64mGy下Fat线性方程：y=0.064x+23.44 (y为LFC，x为VFC，R2=0.868); 64-MDCT组375mA下Fat线性方程：y=0.09x-60.442 (R2=0.994)。结论：辐射剂量对双能量CT物质分离技术定量评估肝脏铁、脂肪沉积无影响；256-MDCT及64-MDCT所测的VIC与LIC、VFC与LFC均呈高度正相关，两个机型在铁定量评估VIC与LIC的相关性、脂肪定量评估VFC与LFC的相关性无差异；本研究为今后临床低辐射剂量CT扫描下定量评估肝脏铁、脂肪沉积奠定基础。     

用EPR对俄罗斯核工人剂量重建

目的:用牙齿珐琅质电子顺磁共振(EPR)对俄罗斯马亚克工厂工人的辐射剂量进行估算,评价用EPR作剂量重建的准确性,比较不同EPR方法在剂量重建的应用经验。方法:用24颗因医学原因拔掉的马亚克工人的牙齿,由(德国)国家环境与健康研究中心(GSF),(俄罗斯)生物物理所(IBP),(俄罗斯)金属物理所(IMP)和(日本)放射线影响研究所(RERF)等4个研究组作EPR测量。每颗牙齿分成两半,分给4个研究组中的2个组测量同一牙齿,每个研究组测量了16个标本。在RERF又将每半个牙齿分成靠近舌和口的内外两个部分进行测量比较。每个实验室按自己的方法进行标…     

The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis.

The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.     

Comparison of sample preparation and signal evaluation methods for EPR analysis of tooth enamel.

In dose reconstruction by EPR dosimetry with teeth various methods are applied to prepare tooth enamel samples and to evaluate the dosimetric signal. A comparison of seven frequently used methods in EPR dosimetry with tooth enamel was performed. The participating Institutes have applied their own procedure to prepare tooth enamel samples and to evaluate the dosimetric signal. The precision of the EPR measurement and the dependence of the estimated dosimetric signal with irradiation up to 1000 mGy were compared. The obtained results are consistent among the different methods. The reproducibility of the dosimetric signal and its estimated relation with the absorbed dose was found to be very close for the applied methods with one possible exception.     

Parameters affecting EPR dose reconstruction in teeth.

The aim of this paper is to analyze the lower limit of detection (LLD), linearity of dose response, variation of radiation sensitivity between different tooth enamel samples, and time/temperature stability of EPR biodosimetry in tooth enamel. The theoretical LLD is shown to be 0.46 mGy, which is far lower than the measured value of about 30 mGy. The main issues to lowering LLD are the differentiation of the radiation-induced component against the total EPR spectrum and the complex nature of the dose dependence of the EPR signal. The following questions are also discussed in detail: need for exfoliated or extracted teeth from persons of interest, accounting for background radiation contribution; conversion of tooth enamel absorbed dose to effective dose; accounting for internal exposure specifically from bone-seeking radionuclides. Conclusions on future development of EPR retrospective biodosimetry are made.     

用牙釉电子自旋共振方法估算慢性辐射损伤人员的受照剂量

目的 用于牙釉电子自旋共振对慢性辐射损伤人员的受照剂量进行估算的方法。方法 用电子自旋共振仪测定慢性辐射损伤人员牙釉电子自旋共振信号强度，用剂量－效应曲线法和附加剂量法来重建辐射损伤人员的受照剂量，探讨牙釉电子自旋共振法估算受照剂量的可行性；并比较了不同能量的射线（1.25MeV的γ射线和6MeV的X射线）对牙釉电子自旋共振信号强度的影响。结果 用两种方法估算的辐射损伤人员受照剂量基本一致；对能量1.25MeV的γ射线和6MeV的X射线进行比较，无论从剂量－效应曲线的直线系数，还是用混合照射后的剂量估算，两者差别不大。结论 慢性辐射损伤人员的受照剂量可以用于牙釉电子自旋共振方法进行估算，射线能量在1.25MeV-6MeV范围内对牙釉电子自旋共振信号强度影响不大。     

EPR spectrum deconvolution and dose assessment of fossil tooth enamel using maximum likelihood common factor analysis.

In order to determine the components which give rise to the EPR spectrum around g = 2 we have applied Maximum Likelihood Common Factor Analysis (MLCFA) on the EPR spectra of enamel sample 1126 which has previously been analysed by continuous wave and pulsed EPR as well as EPR microscopy. MLCFA yielded agreeing results on three sets of X-band spectra and the following components were identified: an orthorhombic component attributed to CO2-, an axial component (CO3(3-)), as well as four isotropic components, three of which could be attributed to SO2-, a tumbling CO2- and a central line of a dimethyl radical. The X-band results were confirmed by analysis of Q-band spectra where three additional isotropic lines were found, however, these three components could not be attributed to known radicals. The orthorhombic component was used to establish dose response curves for the assessment of the past radiation dose, D(E). The results appear to be more reliable than those based on conventional peak-to-peak EPR intensity measurements or simple Gaussian deconvolution methods.     

Tooth enamel EPR dosimetry: sources of errors and their correction.

Some of the most important sources of systematic errors in dose determination using tooth enamel EPR spectroscopy and ways of reducing those errors are discussed. Enamel from the outside of the front teeth should not be used for dose determination because of induction of paramagnetic centers by solar light. The accuracy of the method in the low dose range is limited by variation in the shape of the EPR signal of unirradiated enamel, which can be described by an initial intrinsic signal and which varies for different samples with standard deviation of 20-30 mGy. The energy dependence of enamel sensitivity should be taken into account in the form of a correction factor. The value of this factor is estimated at 1.1-1.3 for real radiation fields in radiation contaminated territories. Variation in enamel sensitivity for different samples is shown to be within limits of 10-15% of the average value.     

Estimation of dose to the unborn child at diagnostic X-ray examinations based on data registered in RIS/PACS

The aim of this work was to determine mean absorbed doses to the unborn child in common conventional X-ray and computed tomography (CT) examinations and to find an approach for estimating foetal dose based on data registered in the Radiological Information System/Picture Archive and Communication System (RIS/PACS). The kerma-area product (KAP) and CT dose index (CTDI_vol) in common examinations were registered using a human-shaped female dosimetry phantom. Foetal doses, D_f, were measured using thermoluminescent dosimeters placed inside the phantom and compared with calculated values. Measured foetal doses were given in relation to the KAP and the CTDI_vol values, respectively. Conversion factor D_f/KAP varies between 0.01 and 3.8 mGy/Gycm², depending on primary beam position, foetus age and beam quality (tube voltage and filtration). Conversion factors D_f/CTDI_vol are in the range 0.02 – 1.2 mGy/mGy, in which the foetus is outside or within the primary beam. We conclude that dose conversion factors based on KAP or CTDI_vol values automatically generated by the RIS/PACS system can be used for rapid estimations of foetal dose for common examination techniques. Ethical Committee: No patients were involved in this study.     

New computer procedure for routine EPR-dosimetry on tooth enamel: description and verification.

A software code was developed for fitting the EPR tooth enamel spectrum using linear combinations of Gaussian functions. The software is fastening EPR dose reconstruction for routine applications. The verification of the software was done comparing with the selective saturation method as an independent procedure of signal evaluation. Both methods were applied for the dose reconstruction of 13 teeth mostly from the Techa riverside. The evaluated doses by the two methods demonstrate an excellent agreement.     

Biophysical dose measurement using electron paramagnetic resonance in rodent teeth.

Electron paramagnetic resonance (EPR) dosimetry of human tooth enamel has been widely used in measuring radiation doses in various scenarios. However, there are situations that do not involve a human victim (e.g. tests for suspected environmental overexposures, measurements of doses to experimental animals in radiation biology research, or chronology of archaeological deposits). For such cases we have developed an EPR dosimetry technique making use of enamel of teeth extracted from mice. Tooth enamel from both previously irradiated and unirradiated mice was extracted and cleaned by processing in supersaturated KOH aqueous solution. Teeth from mice with no previous irradiation history exhibited a linear EPR response to the dose in the range from 0.8 to 5.5 Gy. The EPR dose reconstruction for a preliminarily irradiated batch resulted in the radiation dose of (1.4+/-0.2) Gy, which was in a good agreement with the estimated exposure of the teeth. The sensitivity of the EPR response of mouse enamel to gamma radiation was found to be half of that of human tooth enamel. The dosimetric EPR signal of mouse enamel is stable up at least to 42 days after exposure to radiation. Dose reconstruction was only possible with the enamel extracted from molars and premolars and could not be performed with incisors. Electron micrographs showed structural variations in the incisor enamel, possibly explaining the large interfering signal in the non-molar teeth.