牙釉质电子顺磁共振剂量重建研究的若干进展

介绍了牙釉质电子顺磁共振回顾性剂量学的目前研究概况,着重阐述了低剂量区去除背景信号的新方法,同时也对其在体测量及紫外线影响等方面进行了讨论。     

牙釉质电子顺磁共振剂量重建研究的若干进展

介绍了牙釉质电子顺磁共振回顾性剂量学的目前研究概况，着重阐述了低剂量区去除背景信号的新方法，同时也对其在体测量及紫外线影响等方面进行了讨论。     

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。     

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。本文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进行了讨论。     

电子顺磁共振在体测量指甲剂量方法的可行性研究

目的 针对核应急医学救援剂量评估的需求,为解决指甲电子顺磁共振（EPR）剂量评估方法中机械诱发信号难以分离的问题,探讨指甲EPR在体测量的可行性。方法 利用自研的指甲在体EPR测量装置,对未剪碎指甲进行整体测量,在无机械诱发信号干扰的条件下研究指甲的本底信号及辐射诱发信号特性,探索通过水处理恢复本底信号的方法;开展指甲实际在体EPR测量实验,评价在体测量条件对EPR波谱的影响。结果 未剪碎指甲的本底信号分布服从正态分布,不同性别志愿者的指甲本底信号差异无统计学意义（P>0.05）;在2~10 Gy范围内建立了剂量响应关系,指甲辐射诱发信号半衰期约为5 d;建立了变温结合水处理的本底信号恢复方法,处理后指甲EPR信号与本底信号差异无统计学意义（P>0.05）;获得了实际在体测量条件下的指甲EPR波谱。结论 利用本方法可以获得不含有机械诱发信号的EPR波谱,初步验证了指甲在体EPR测量用于剂量评估的可行性。     

牙釉质EPR谱去卷积程序在剂量重建中的应用

目的探讨牙釉质电子顺磁共振(EPR)谱去卷积程序在小剂量区域剂量重建的应用。方法用编写的EPR谱拟合程序拟合一系列用不同小剂量照射过的牙釉质样品EPR谱，得到相应的剂量信号(RIS)强度，线性回归得到剂量响应曲线，并分析拟合精度。结果剂量响应曲线IRIS=14．04 0．768D(mGy)，r=0．997，SD=19．8mGy。结论这项技术将牙釉质EPR剂量重建的下限降低到约200mGy。     

民航飞行人员宇宙辐射受照剂量的估算

目的计算被检测飞行人员个人宇宙辐射年均受照有效剂量。方法根据飞行指令数据使用美国联邦航空署开发的软件CARI 6,计算飞行航线的宇宙辐射有效剂量和乌鲁木齐地区地面的宇宙辐射有效剂量率 ,由运行软件输出数据计算个人年均受照有效剂量。结果乌鲁木齐地区地面个人年均受照有效剂量为 0 .42 0mSv ,新疆航空公司全部航线 1 997～ 1 999年平均宇宙辐射有效剂量率为 2 .381 μSv·h- 1 ( 0 .33～ 3.64μSv·h- 1 )。被检测飞行人员年均受照有效剂量为 2 .1 93mSv·a- 1 ( 0 .887～ 4.41 9mSv·a- 1 )。结论估算的 2 34个受检飞行人员的年均受照有效剂量均小于国际放射防护委员会 (ICRP)建议的限值 2 0mSv·a- 1 。     

两种剂量估算方法在成人胸部CT辐射剂量评估中的应用价值

目的 探讨容积CT剂量指数（CTDI_vol）与体型特异性剂量估算（SSDE）两种辐射剂量估算方法在评估成人胸部CT扫描辐射剂量中的应用价值。方法 回顾性分析2017年3月至4月浙江中医药大学附属第一医院128例进行胸部CT平扫且所有图像均能满足诊断要求的受检者的CTDI_vol与SSDE。将受检者按照不同体质量指数（BMI）分为3组：A组,16 ≤ BMI<21.1 kg/m²,38例;B组,21.1 ≤ BMI<23.9 kg/m²,53例;C组,23.9 ≤ BMI<34.1 kg/m²,37例。在两乳头层面测量每例受检者的前后径（AP）、左右径（LAT）,记录每例受检者的CTDI_vol值,计算每例受检者的有效直径（ED）、转换因子（f_size）和SSDE。同时,比较不同体质量指数组CTDI_vol与SSDE之间的差异。结果 3组受检者的SSDE均高于CTDI_vol,A、B、C组分别增加了50.13%、42.83%、33.68%。CTDI_vol和SSDE估算方法3组辐射剂量比较差异均有统计学意义（t=-48.873、-57.001、-32.651,P<0.05）。3组受检者间的ED、f_size、CTDI_vol和SSDE差异均有统计学意义（F=51.456、47.749、113.916、106.449,P<0.05）。结论 SSDE能够评估不同体型的受检者在胸部CT扫描中所受到的辐射剂量,而CTDI_vol过低地估计了受检者受到的辐射剂量,且BMI越小的受检者被低估的剂量值越大,实际受到的辐射剂量越多。     

碱性单细胞凝胶电泳技术用于淋巴细胞辐射生物剂量估算初探

目的 初步探索碱性单细胞凝胶电泳（SCGE）方法用于电离辐射生物剂量估算的可行性.方法 不同剂量水平（0～5 Gy）的60Co γ射线照射正常人外周血,用碱性SCGE分析淋巴细胞“彗星”尾长和尾矩,建立各自的剂量-效应曲线.收集某基地放射工作从业人员的外周血进行碱性SCGE分析,并估算受照剂量,与监测物理剂量相比较.结果 淋巴细胞“彗星”尾长和尾矩均随着照射剂量的增加而增加,其剂量-效应曲线均为线性平方模式.以“彗星”尾长为指标的剂量-效应曲线方程为Y=13.59＋20.87X-2.27X^2,以尾矩为指标的曲线方程为Y=8.50＋15.04X-1.43X^2.参照上述方程,以尾矩为指标估算放射工作从业人员的剂量更接近实际受照剂量.结论 用碱性SCGE分析淋巴细胞“彗星”尾矩有希望成为电离辐射生物剂量计.     

CT检查所致病人剂量的简便估算方法

ＣＴ检查给予病人很高的辐射剂量。通常人们采用器官剂量和有效剂量来评价病人所受剂量 ,并将有效剂量做为评价辐射随机效应危险度指数。为了得到ＣＴ检查病人的器官剂量和有效剂量 ,人们通常采用两种方法。一种是使用人体等效体模和热释光剂量计直接测量出组织或器官的器官剂量 ;另一种是基于测量的ＣＴ剂量学指数 (ＣＴＤＩ)并利用归一器官剂量转换因子计算出组织或器官的器官剂量。第 1种方法比较烦琐 ;第 2种方法由于某些ＣＴ装置归一器官剂量转换因子的缺乏难于计算。针对这一情形 ,人们提出了权重ＣＴ剂量学指数 (ＣＴＤＩＷ )和剂量…     

电离辐射诱导小鼠骨电子顺磁共振信号检测的影响因素

目的 研究影响小鼠骨辐射诱导电子顺磁共振（EPR）信号检测的因素。 方法 将小鼠股骨去除软组织和骨髓,干燥,制成股骨段,经60Co γ射线照射,照射剂量率为5 Gy/min,照射剂量为10 Gy和50 Gy。检测不同干燥程度、检测方向、微波功率和叠加次数等条件下骨EPR的信号强度。 结果 降低骨样品含水量、设置合适的微波功率、增加叠加次数均可以增加样品信号强度,且不同检测方向下同一份样品的信号强度有一定差异。 结论 适当的样品预处理和检测参数设定可以提高骨EPR检测的灵敏度,样品多方向检测并取平均值可减弱骨样品不均一产生的影响。     

Estimation of X-ray beam quality by electron paramagnetic resonance (EPR) spectroscopy

A novel dosimetry-based technique using EPR spectroscopy to determine X-ray beam quality is proposed. The radiation-sensitive material is made of a mixture of two polycrystalline substances with different X-ray absorption properties.

The composite samples, consisting of polycrystalline lithium formate monohydrate and calcium formate, were prepared as pellets, X-irradiated, and analyzed with EPR spectroscopy. The ratio of the EPR signal amplitudes of the two constituents can serve as a measure of the X-ray beam quality given by the equivalent photon energy. The calculation of the signal amplitude ratio involves a reconstruction of the composite EPR spectrum. The logarithm of the signal amplitude ratio appears to be linearly correlated with the logarithm of the equivalent photon energy. The linear relationship can be used as a calibration for estimating the equivalent photon energy from the composite EPR spectrum.

The composite material was used to investigate the changes in the equivalent photon energy in a Perspex phantom with increasing depth. When a 220 kV X-ray beam with an equivalent photon energy of about 100 keV was used, changes in the EPR signal amplitude ratio revealed a buildup of scattered photons with increasing depth in the phantom. This change could be related to the equivalent photon energy using the logarithmic calibration curve. It was found that the equivalent photon energy at the depth of 13 cm in the phantom was 25% lower than on its surface.

The proposed method can be used for estimating equivalent photon energy in both standardized and non-standardized situations, the latter corresponding to beam setups where use of filters and ionization chambers is difficult or impossible. Also, the system can provide a means for measuring photon energy in X-irradiated phantoms.     

电子顺磁共振在生物医学研究中的应用

电子顺磁共振技术从被发现到现在已有半个多世纪,由于它可以直接对自由基进行检测,现已应用到各种研究领域,推动着生物医学事业的发展。该文主要概述了现阶段电子顺磁共振所研究的生物组织内的各种自由基,以及自旋标记、电子顺磁共振成像技术在生物医学研究中的应用。     

Feasibility and assessment of non-invasive in vivo redox status using electron paramagnetic resonance imaging

Purpose:
To test the feasibility of electron paramagnetic resonance imaging (EPRI) to provide non-invasive images of tissue redox status using redox-sensitive paramagnetic contrast agents. Material and Methods:
Nitroxide free radicals were used as paramagnetic agents and a custom-built 300 MHz EPR spectrometer/imager was used for all studies. A phantom was constructed consisting of four tubes containing equal concentrations of a nitroxide. Varying concentrations of hypoxanthine/xanthine oxidase were added to each tube and reduction of the nitroxide was monitored by EPR as a function of time. Tumor-bearing mice were intravenously infused with a nitroxide and the corresponding reduction rate was monitored on a pixel-by-pixel basis using 2D EPR of the tumor-bearing leg and normal leg serving as control. For animal studies, nitroxides were injected intravenously (1.25 mmol/kg) and EPR projections were collected every 3 min after injection using a magnetic field gradient of 2.5 G/cm. The reduction rates of signal intensity on a pixel-by-pixel basis were calculated and plotted as a redox map. Redox maps were also collected from the mice treated with diethylmaleate (DEM), which depletes tissue thiols and alters the global redox status. Results:
Redox maps obtained from the phantoms were in agreement with the intensity change in each of the tubes where the signals were decreasing as a function of the enzymatic activity, validating the ability of EPRI to accurately access changes in nitroxide reduction. Redox imaging capability of EPR was next evaluated in vivo. EPR images of the nitroxide distribution and reduction rates in tumor-bearing leg of mice exhibited more heterogeneity than in the normal tissue. Reduction rates were found to be significantly decreased in tumors of mice treated with DEM, consistent with the depletion of thiols and the consequent alteration of the redox status. Conclusion:
Using redox-sensitive paramagnetic contrast agents, EPRI can non-invasively discriminate redox status differences between normal tissue and tumors.     

Uncertainties in alanine dosimetry in the therapeutic dose range

A method for evaluating the overall uncertainty of alanine EPR transfer dosimetry in the therapeutic dose range is described. The method uses experimental data on EPR signal reproducibility from replicate dosimeters irradiated to low doses (1–5 Gy), estimates of Type B uncertainties, and Monte Carlo simulations of heteroscedastic orthogonal linear regression. A Bruker ECS106 spectrometer and Bruker alanine dosimeters have been used for this evaluation. The results demonstrate that alanine dosimetry can be used for transfer dosimetry in that range with the overall uncertainty 1.5–4% (1σ) depending on the dose, the number of replicate dosimeters, and the duration of the calibration session (the session should not exceed one working day).     

Electron paramagnetic resonance monitoring of ischemia-induced myocardial oxygen depletion and acidosis in isolated rat hearts using soluble paramagnetic probes

A new low-field electron paramagnetic resonance approach for noninvasive measurements of myocardial oxygen tension and tissue acidity was developed. The approach was applied to monitor myocardial pO(2) and pH in a model of global no-flow ischemia (30 min) and reperfusion in isolated perfused rat hearts. The myocardial oxygen measurements were performed using deuterated Finland trityl radical probe. A rapid decrease in myocardial pO(2) from 160 mmHg to about 2 ± 1 mmHg was observed within the first minute of ischemia followed by incomplete restoration of pO(2) to 50 mmHg during 30 min of reperfusion. The lower oxygen concentration after ischemia was attributed to the 50% reduction in coronary flow after ischemia as a consequence of myocardial ischemia and reperfusion damage. Myocardial pH measurements using a specially designed imidazoline pH-sensitive nitroxide showed severe myocardial acidification to pH 6.25 during 30 min of ischemia. Preconditioning of the hearts with two 5-min periods of ischemia significantly reduced the acidification of myocardial tissue during sustained ischemia. Noninvasive electron paramagnetic resonance monitoring of myocardial oxygenation and pH may provide important insights into the mechanisms of ischemia and reperfusion injury and a background for development of new therapeutic approaches.