医用X射线摄影所致受检者体表剂量估算方法进展

目的:探讨医用X射线摄影所致受检者入射体表剂量的估算模式,为掌握受检者与患者的剂量水平提供技术支持,并为制定相应的防护措施提供理论依据。方法:对目前已有的普通X射线摄影和数字X射线摄影两大类医用X射线装置中涉及到受检者入射体表剂量估算的研究论文进行归纳和总结,并对相应方法的原理和应用进行探讨,比较各类方法的优点和缺点。结果:普通X射线摄影估算模式的数学模型简单,计算便捷,但相应的曝光参数获取不易,且由于模型相对简化,可能因机型、照射野、受检者及其他摄影条件的差异,导致估算时产生较大的偏差。数字X射线摄影估算模式则不需要进行多余的测量及记录,可根据每次摄影后系统给出的曝光指示值或者DAP值来推算出受检者的入射体表剂量,但在该类方法中,受检部位厚度的不确定性会致使结果存在较大差异。结论:目前现存的用于估算医用X射线摄影所致受检者入射体表剂量的模型仍存在较大差异和不足,其中数字X射线摄影估算方法有较大应用前景,仍有待进一步发展和探索。     

降低儿童X射线CT检查辐射剂量的研究进展

目的：归纳总结减少儿童X射线CT检查所致受检者辐射剂量的方法,为降低儿童接受X射线CT检查的辐射危害风险提供参考。方法：针对X射线CT检查所致儿童的辐射剂量,通过调研相关文献,基于各自研究的目的和原理,归纳总结降低儿童受照剂量的方法。结果：自动管电流调制技术能根据儿童受检者体型自行改变管电流,自动管电压选择技术能根据预先设定的影像质量水平并结合X射线在受检者的衰减自动选择管电压,这两种技术均能自动降低个体的受照剂量;先进的影像重建技术可减少低剂量扫描影像的噪声,间接起到降低个体和群体的受照剂量;非扫描区的合理屏蔽也能有效降低个体和群体的受照剂量;制定剂量参考水平有助于优化X射线CT检查扫描参数,起到降低群体受照剂量的作用。结论：可结合儿童受检者的体型、扫描部位以及X射线CT机的性能,综合运用自动管电流或管电压调制技术、影像重建技术以及屏蔽防护等多种方法,可最大限度地降低儿童X射线CT检查的受照剂量。     

数字摄影如何降低受检者辐射剂量

在计算机X射线摄影（computed radiography,CR）、数字化X射线摄影（digitalradiography,DR）技术广泛应用的今天,这些新技术给人们的健康作出贡献的同时,也给受检者带来辐射剂量的增加,这对受检者的潜在危害也越来越大。那么,探索如何尽量减少受检者辐射剂量,仍然是放射技术人员应当关注的问题。     

甲状腺-乳腺防护衣在乳腺X线摄影中降低辐射剂量的研究

目的:采用屏蔽防护法屏蔽和降低乳腺X射线摄影中散射辐射对受检者甲状腺及乳腺所致辐射剂量的方法,并对其采用防护措施的防护效果进行试验研究。方法:在数字化乳腺X射线摄影(DR)中,随机选取30例乳腺X射线受检者,采用本中心新研制的0.5 mm Pb铅橡胶甲状腺-乳腺防护衣对受检者进行屏蔽。采集数据方法:在防护衣内侧和外侧分别各放置一组LiF(Mg·Cu·P)热释光剂量探测器,在同一检测条件下进行照射后,分别测量甲状腺-乳腺防护衣内侧和外侧两组入射空气比释动能数值。结果:防护衣内外入射空气比释动能的差异具有统计学意义(P0.05)。防护衣对甲状腺的防护效率为(99.25±0.99)%,对侧乳腺的防护效率为(99.17±1.03)%。结论:甲状腺-乳腺防护衣可以降低甲状腺和乳腺在X射线摄影时的散射辐射,并且屏蔽防护效果显著。     

一种基于压缩传感理论的CT剂量降低方法

目的X射线计算机断层成像技术（computed tomography,CT）辐射剂量高于其它X射线检测。因为剂量累积效应会导致较高的致癌风险,因此降低剂量成为当前CT技术发展过程中亟待解决的问题。方法降低剂量的手段主要有降低管电流和增加探测器排数,但受相关因素制约,进一步降低剂量面临较大困难。本文提出一种基于X射线衰减水平的自适应非均匀采样方式,通过减少在高管电流区域的投影次数来降低剂量,并引入基于压缩传感的POCS—TVM算法从欠采样数据中恢复CT图像。结果实验结果表明该方法能在保证图像质量的同时有效降低剂量。结论基于压缩传感理论的CT剂量降低方法可以在保证重建图像满足临床诊断需求的前提下,有效降低辐射剂量,有利于受检者。     

DAP电离室的研制及其特性研究

目的：研制适用于医学诊断X线摄影被检者照射量监测的电离室，并对其各种输出特性进行实验测量研究。材料与方法：整个电离室采用平行板电极，收集电极采用静电喷涂石墨电极，即不会在胶片上形成影像又不增加电离室对射线采吸收。结果与结论：所研制的电离室对有用X线束吸收少，其信号输出与输入线量强度及照射野面积呈良好线性，且线质响应均匀。     

医用质子加速器扩展束流与笔形束流的感生放射性辐射剂量

目的:通过比较医用质子加速器两种不同束流引出方式的X/γ射线感生放射性辐射剂量差异,从而采取相应措施降低治疗室的环境辐射水平,减少医用质子加速器工作人员的累积辐射剂量。方法:模拟患者治疗的肿瘤辐射野,分别在质子加速器扩展束流治疗室和笔形束流治疗室进行15 CGE的质子射线照射,射线停止60 s后,进入治疗室利用两台Neutron RAE II检测仪同时对射线输出窗口和治疗床等中心这两个位置进行X/γ射线感生放射性辐射剂量测量,并记录数据。按以上出束条件和测量步骤,重复测量3次,每次间隔30 min。结果:扩展束流射线输出窗的3次测量值依次为32.3、63.2、70.1μSv/h,在治疗床等中心的3次测量值依次为4.5、5.6、7.7μSv/h,两个测量点的感生放射性辐射剂量率均随着测量次序依次增加。笔形束流射线输出窗的3次测量值依次为3.2、2.3、2.1μSv/h,在治疗床等中心的3次测量值依次为0.21、0.18、0.18μSv/h,两个测量点的感生放射性辐射剂量率均与测量次序无关。在输出窗位置,扩展束流的测量平均值是笔形束流测量平均值的21.8倍;在治疗床等中心位置,扩展束流的测量平均值是笔形束流测量平均值的31.2倍。结论:在出束剂量和时间相同的情况下,笔形束流的感生辐射剂量较小,其机房环境辐射水平远远低于扩展束流机房,对工作人员有更好的保护作用。     

电离室矩阵用于加速器质量保证：X射线

目的：探讨利用二维电离室矩阵MatriXX进行医用直线加速器质量保证的方法及可靠性。方法：在点剂量的质量保证中。将MatriXX系统在特制水箱中测得的数据与O．6CC电离室在标准水箱中的剂量测量值作比较,从而定出Ma．triXX的校准系数．以此来校准射线的输出量和能量。在面剂量的质量保证中,用MatriXX测量医用加速器射线野的对称性、平坦度以及辐射野的大小及中心轴偏离．将测量结果与RFA300三维水箱扫描结果及控制台显示数值进行比较分析。结果：用MatriXX加有机玻璃板可准确快捷地完成对射线输出量和能量的校准。用MatriXX所测射野的对称性和平坦度及射线野大小与RFA300水箱的测量数据一致。结论：MatriXX系统进行加速器的质量保证简便可靠。     

CR静脉肾盂造影图像质量与X射线剂量的探讨

目的探讨计算机X射线摄影（CR）在静脉肾盂造影应用中以满足图像诊断质量和X射线曝光参数（kVp、mAs）的优化组合,使X射线剂量控制在最低,降低被检者的有害X射线辐射量。方法对3组不同体型厚度（18cm、22cm、26cm）的被检者,对每组分别以常规摄影条件,增加kVp、降低mAs进行摄影。以kVp与mAs组合图像质量完全满足诊断要求,剂量最低的参数作为最优参考曝光参数。用体模替代3种被检者体型厚度,用同样摄影曝光参数,分别测量体表、体后及有关被检者器官组织的吸收X射线剂量。结果与常规摄影相比,被检者的X射线吸收剂量平均降低了31.97%,面积乘积剂量平均降低了34.57%,有效剂量降低了33.98%。结论在静脉肾盂造影中用CR成像技术与投照参数优化组合,对降低被检者的X射线吸收剂量是行之有效的,为其他投照部位用CR或数字X射线摄影（DR）数字成像参数优化组合研究提供了指导性的方法,有一定的临床应用价值。     

DR组织均衡技术在低剂量鼻骨侧位X射线摄影中的应用

目的探寻在鼻骨侧位X射线摄影中利用数字化X射线摄影(DR)组织均衡技术获取满足诊断需要的图像并降低患者辐射剂量的研究。方法利用人体模型进行常规的鼻骨侧位摄影,然后固定千伏值,在原有的mAs值上分别降低0.4、0.8、1.2 mAs进行摄片,再将降低剂量的图像采用DR组织均衡技术进行处理,比较不同图像对于满足诊断的需要和患者所接受的辐射剂量。结果常规摄影技术得到的图像需反复调节不同的窗宽、窗位才能显示密度、厚度不同的鼻骨与软组织;降低0.4、0.8 mAs,虽然图像的空间分辨率降低,但是采用DR组织均衡技术可在同一幅图像上清晰显示鼻骨与邻近软组织结构,同时降低患者的辐射剂量;降低1.2 mAs,不但图像的空间分辨率降低,而且无法采用DR组织均衡技术使图像达到满足诊断需要。结论采用DR组织均衡技术不仅能将密度、厚度不同的鼻骨及邻近软组织在同一副图像上清晰显示,而且能够有效降低患者的辐射剂量。     

Bootstrap resampling: a powerful method of assessing confidence intervals for doses from experimental data

Bootstrap resampling provides a versatile and reliable statistical method for estimating the accuracy of quantities which are calculated from experimental data. It is an empirically based method, in which large numbers of simulated datasets are generated by computer from existing measurements, so that approximate confidence intervals of the derived quantities may be obtained by direct numerical evaluation. A simple introduction to the method is given via a detailed example of estimating 95% confidence intervals for cumulated activity in the thyroid following injection of 99mTc-sodium pertechnetate using activity-time data from 23 subjects. The application of the approach to estimating confidence limits for the self-dose to the kidney following injection of 99mTc-DTPA organ imaging agent based on uptake data from 19 subjects is also illustrated. Results are then given for estimates of doses to the foetus following administration of 99mTc-sodium pertechnetate for clinical reasons during pregnancy, averaged over 25 subjects. The bootstrap method is well suited for applications in radiation dosimetry including uncertainty, reliability and sensitivity analysis of dose coefficients in biokinetic models, but it can also be applied in a wide range of other biomedical situations.     

Normalized conceptus doses for abdominal radiographic examinations calculated using a Monte Carlo technique

The aim of the present study was to develop a reliable method for estimating conceptus radiation doses resulting from abdominal radiographic examinations for all trimesters of pregnancy. The method is based on normalized conceptus doses estimated using Monte Carlo modeling. The Monte Carlo N-Particle (MCNP) radiation transport code was employed in the current study. The validity of the MCNP computational approach was verified by comparison with dose data obtained in anthropomorphic phantoms simulating pregnancy at the three trimesters of gestation using thermoluminescence dosimetry (TLD). The results consist of radiation doses normalized to air kerma so that conceptus dose from any technique and x-ray unit used for abdominal radiography can be easily calculated. Normalized conceptus doses are presented for the first, second, and third trimesters of gestation for various kVp and total beam filtration values. Data apply to radiographic systems equipped with high frequency or 3 phase 12 pulse generators. A very good agreement was observed between the normalized conceptus doses estimated by TLD measurements and the MCNP simulation for all periods of gestation (maximum difference 8.1%). The results of MCNP procedures were compared to published data obtained by TLD measurements. Normalized conceptus dose values agree well, with most differences being lower than 10%. The normalized doses obtained in the current study are dependent on field size. However, for small changes in the size of the x-ray field, the change in normalized doses is not considerable. Accurate estimation of conceptus doses due to abdominal conventional x-ray examinations can be made using the dose data provided in the current study.     

数字X射线摄影机床边胸部摄影时周围散射线量测量

目的测量移动式数字X射线摄影（DR）机床边胸部摄影时照射野外的散射线辐射剂量。方法采用移动式DR机,用80kV、240mA、10ms和110cm焦-片距,垂直照射胸部体模,将测量仪分别放在360°均等分的8个角度、距照射野外1m和2m处,共测16个点。结果在0°和180°2m远距离处,测量仪上散射线量指示值最大,均为0.014μSv。在90°和270°2m远距离处最小,分别为0.011μSv和0.010μSv。结论一次移动式DR床边机胸部摄影,如患者和工作人员距照射野外2m远,其散射线辐射剂量低于人体7min所接受的自然本底照射剂量,不会产生危害后果。     

电子顺磁共振技术在生物样品辐射剂量重建中的应用研究进展

电子顺磁共振技术可用于检测样品中的顺磁分子,可在较短时间内完成辐射剂量的重建,对于大范围辐射事故人群的剂量重建、分类诊治和医用X线人员辐射流行病学研究具有重要的现实意义。该文首先介绍了电子顺磁共振技术的基本原理和应用现状,该技术可直接检测物质中的顺磁分子,可在较短时间内提供吸收剂量的评估结果;然后分别从牙齿、指甲和其他生物样品的电子顺磁共振辐射剂量重建的应用现状与进展展开了综述,上述样品在剂量重建中均有优劣势,但在剂量重建的灵敏度和准确性方面需进一步研究,该综述以期为电子顺磁共振技术在生物样品剂量重建的相关研究提供新思路,为电子顺磁共振技术的进一步推广应用奠定基础。 【关键词】电子顺磁共振技术;生物样品;剂量重建;综述     

Reconstructive dosimetry for cutaneous radiation syndrome

According to the International Atomic Energy Agency (IAEA), a relatively significant number of radiological accidents have occurred in recent years mainly because of the practices referred to as potentially high-risk activities, such as radiotherapy, large irradiators and industrial radiography, especially in gammagraphy assays. In some instances, severe injuries have occurred in exposed persons due to high radiation doses. In industrial radiography, 80 cases involving a total of 120 radiation workers, 110 members of the public including 12 deaths have been recorded up to 2014. Radiological accidents in industrial practices in Brazil have mainly resulted in development of cutaneous radiation syndrome (CRS) in hands and fingers. Brazilian data include 5 serious cases related to industrial gammagraphy, affecting 7 radiation workers and 19 members of the public; however, none of them were fatal. Some methods of reconstructive dosimetry have been used to estimate the radiation dose to assist in prescribing medical treatment. The type and development of cutaneous manifestations in the exposed areas of a person is the first achievable gross dose estimation. This review article presents the state-of-the-art reconstructive dosimetry methods enabling estimation of local radiation doses and provides guidelines for medical handling of the exposed individuals. The review also presents the Chilean and Brazilian radiological accident cases to highlight the importance of reconstructive dosimetry.     

工频X线机和中频X线机在胸部计算机X线摄影中应用分析

目的分析工频X线机和中频X线机在胸部计算机X线摄影(CR)中的图像质量,监测相应辐射剂量,比较两种X线机在CR摄影中的适用性。方法使用工频X线机和中频X线机摄取2～3岁小儿胸片共28例,分析图像质量,监测辐射剂量;并对两种X线机高压输出及IP对X线吸收特点进行分析。结果同工频X线机相比,中频X线机更易获得优质图像,且降低了辐射剂量。结论在CR应用中,中频X线机比工频X线机有明显优势。     

Calculation of effective dose

The concept of "effective dose" was introduced in 1975 to provide a mechanism for assessing the radiation detriment from partial body irradiations in terms of data derived from whole body irradiations. The effective dose is the mean absorbed dose from a uniform whole-body irradiation that results in the same total radiation detriment as from the nonuniform, partial-body irradiation in question. The effective dose is calculated as the weighted average of the mean absorbed dose to the various body organs and tissues, where the weighting factor is the radiation detriment for a given organ (from a whole-body irradiation) as a fraction of the total radiation detriment. In this review, effective dose equivalent and effective dose, as established by the International Commission on Radiological Protection in 1977 and 1990, respectively, are defined and various methods of calculating these quantities are presented for radionuclides, radiography, fluoroscopy, computed tomography and mammography. In order to calculate either quantity, it is first necessary to estimate the radiation dose to individual organs. One common method of determining organ doses is through Monte Carlo simulations of photon interactions within a simplified mathematical model of the human body. Several groups have performed these calculations and published their results in the form of data tables of organ dose per unit activity or exposure. These data tables are specified according to particular examination parameters, such as radiopharmaceutical, x-ray projection, x-ray beam energy spectra or patient size. Sources of these organ dose conversion coefficients are presented and differences between them are examined. The estimates of effective dose equivalent or effective dose calculated using these data, although not intended to describe the dose to an individual, can be used as a relative measure of stochastic radiation detriment. The calculated values, in units of sievert (or rem), indicate the amount of whole-body irradiation that would yield the equivalent radiation detriment as the exam in question. In this manner, the detriment associated with partial or organ-specific irradiations, as are common in diagnostic radiology, can be assessed.     

Calculation of organ doses in x-ray examinations of premature babies

Lung disease represents one of the most life-threatening conditions in prematurely born children. In the evaluation of the neonatal chest, the primary and most important diagnostic study is the chest radiograph. Since prematurely born children are very sensitive to radiation, those radiographs may lead to a significant radiation detriment. Knowledge of the radiation dose is therefore necessary to justify the exposures. To calculate doses in the entire body and in specific organs, computational models of the human anatomy are needed. Using medical imaging techniques, voxel phantoms have been developed to achieve a representation as close as possible to the anatomical properties. In this study two voxel phantoms, representing prematurely born babies, were created from computed tomography- and magnetic resonance images: Phantom 1 (1910 g) and Phantom 2 (590 g). The two voxel phantoms were used in Monte Carlo calculations (MCNPX) to assess organ doses. The results were compared with the commercially available software package PCXMC in which the available mathematical phantoms can be downsized toward the prematurely born baby. The simple phantom-scaling method used in PCXMC seems to be sufficient to calculate doses for organs within the radiation field. However, one should be careful in specifying the irradiation geometry. Doses in organs that are wholly or partially outside the primary radiation field depend critically on the irradiation conditions and the phantom model.     

An Automated DICOM Database Capable of Arbitrary Data Mining (Including Radiation Dose Indicators) for Quality Monitoring

The U.S. National Press has brought to full public discussion concerns regarding the use of medical radiation, specifically x-ray computed tomography (CT), in diagnosis. A need exists for developing methods whereby assurance is given that all diagnostic medical radiation use is properly prescribed, and all patients’ radiation exposure is monitored. The “DICOM Index Tracker©” (DIT) transparently captures desired digital imaging and communications in medicine (DICOM) tags from CT, nuclear imaging equipment, and other DICOM devices across an enterprise. Its initial use is recording, monitoring, and providing automatic alerts to medical professionals of excursions beyond internally determined trigger action levels of radiation. A flexible knowledge base, aware of equipment in use, enables automatic alerts to system administrators of newly identified equipment models or software versions so that DIT can be adapted to the new equipment or software. A dosimetry module accepts mammography breast organ dose, skin air kerma values from XA modalities, exposure indices from computed radiography, etc. upon receipt. The American Association of Physicists in Medicine recommended a methodology for effective dose calculations which are performed with CT units having DICOM structured dose reports. Web interface reporting is provided for accessing the database in real-time. DIT is DICOM-compliant and, thus, is standardized for international comparisons. Automatic alerts currently in use include: email, cell phone text message, and internal pager text messaging. This system extends the utility of DICOM for standardizing the capturing and computing of radiation dose as well as other quality measures.Key words: Data extraction, medical informatics applications, radiation dose, database management systems, knowledge base