精细乳房模型及其在乳腺X射线摄影剂量评估中的应用

乳腺是对辐射致癌最敏感的组织之一,而辐射致癌风险与受照剂量密切相关。为更准确地评估电离辐射所致乳腺受照剂量,本文建立了一个具有皮肤、皮下脂肪、乳房后侧脂肪、悬吊韧带、纤维腺体区脂肪、输乳管、小叶、输乳窦和乳头等精细结构的乳房数学模型,并将其体素化为体素模型。考虑到在乳腺X射线摄影中的应用,对乳房体素模型进行头尾位（CC位）压迫,建立压迫乳房模型,并与中国成年女性参考人体素体模（CRAF）相拼接。采用Geant4对乳腺X射线摄影进行蒙特卡罗模拟,计算了一系列平均腺体剂量转换因子。根据计算结果,采用精细乳房模型计算的平均腺体剂量转换因子低于我国现行国家标准的取值,但与美国放射学会（ACR）标准的取值差别不大。     

数字乳腺X射线摄影成像参数优化研究

为使女性受检者接受尽量低的剂量同时获得尽量好的图像质量,本文针对Hologic Lorad Selenia数字乳腺X射线机型进行了数字乳腺X射线摄影成像参数优化研究。采用不同靶/滤过组合、管电压,对不同厚度和腺体百分含量的乳腺模体成像,获得不同成像参数下图像的对比度噪声比,用于表征图像质量。采用适用于中国女性的平均腺体剂量转换因子,计算数字乳腺X射线摄影中受检者的受照剂量,进而探究图像质量一致的情况下,受检者的受照剂量随不同成像参数的变化规律,最终对适用于中国女性的数字乳腺X射线摄影成像参数给出建议。本文结果为中国女性数字乳腺X射线摄影成像参数的优化提供参考。     

蒸压加气混凝土砌块辐射防护屏蔽性能试验研究

本文利用相同管电流(25 mA)不同管电压(70 kV~120 kV)下产生的X射线,对国内4种常用蒸压加气混凝土砌块样品进行照射,并测量射线穿过每种样品后固定点位处的空气吸收剂量率。研究得出:(1)在70 kV～120 kV条件下,蒸压加气混凝土砌块的等效铅当量厚度随着管电压的增加出现先增加后减小的变化趋势,在90 kV时达到最大;(2)4种蒸压加气混凝土砌块的等效铅当量厚度均大于1.0 mm,部分射线装置机房可选用蒸压加气混凝土作为辐射防护材料;(3)蒸压加气混凝土砌块的等效铅当量厚度与材料的干密度、厚度有关,与抗压强度无关,材料的干密度越大、材料厚度越大,等效铅当量厚度越高。     

医用乳腺X射线参考辐射场的建立

本文主要介绍医用乳腺X射线标准装置的设计及参考辐射场的测量。装置设计方面包括:使用了常用于乳腺诊断的两种靶型,配置了不同大小限束光阑,装备了光学平台和移动导轨装置。实验测量方面包括:辐射束准直性测量、辐射野均匀性测量和半值层测量。结果:辐射束满足准直性要求、辐射野满足均匀性要求,半值层测量结果显示辐射质达到既定要求;该标准装置能够满足用于乳腺X射线计量仪表的检定和校准。     

湖南省数字X射线摄影设备(DR)主要检查类型所致受检者剂量水平调查

为了解湖南省X射线摄影设备(DR)6种主要检查部位不同的投照方位所致受检者的剂量水平,采用典型抽样法,在省内选取967例受检者作为调查样本,对常用的几种投照类型所致受检者的剂量进行调查。结果表明,湖南省内X射线摄影设备(DR),在腰椎前后位投照(AP)、腰椎侧位投照(LAT)、骨盆前后位投照(AP)、髋关节前后位投照(AP)、胸部后前位投照(PA)、胸部侧位投照(LAT)、胸椎前后位投照(AP)、胸椎侧位投照(LAT)、头颅后前位投照(PA)、头颅侧位投照(LAT)等部位投照时,所致受检者剂量的典型值分别为3.9、5.7、2.5、3.8、0.3、0.7、1.3、3.0、 0.7和0.7 mGy。无自动曝光控制(AEC)时,DR在胸部PA、胸部LAT摄影时所致受检者的剂量的平均值分别为0.77 mGy和1.44 mGy,有AEC时,DR在胸部PA、胸部LAT摄影时所致受检者的剂量的平均值分别为0.27 mGy和0.56 mGy。湖南省X射线摄影设备(DR)6种主要检查部位不同的投照方位所致受检者的剂量低于GB 18871—2002《电离辐射防护与辐射源安全基本标准》给出的典型成年受检者X射线摄影的剂量指导水平。在一定程度上, AEC能优化受检者在X射线摄影检查中受到的辐射剂量。     

乳腺肿瘤组织中的微量元素分析

用同步辐射X射线荧光(SR-XRF)技术分析了正常乳腺组织、良性乳腺肿瘤组织和乳腺癌组织中微量元素的种类、相对含量等.根据SR-XRF的结果,在这三种组织中微量元素的种类是相同的,但相对含量是不相同的,特别是正常组织和肿瘤组织中的Ca、Fe和Zn的差异相当明显.肿瘤组织中S、Cr、Mn、Ni、Cu和Se的相对含量与正常组织中含量具有正相关性,即肿瘤组织的含量相对于正常组织是增加的,而K和Ca则是负相关性.P在正常乳腺组织和良性乳腺肿瘤组织中的含量基本不变,但在癌变组织中略有下降.恶性肿瘤中的Fe和Zn是正相关性,而在良性肿瘤中则是负相关性.可见:正常、良性和癌变的乳腺组织中微量元素的相对含量是不同的,可以为乳腺癌的诊断提供有用信息.     

上海市“十一五”期间X射线诊断的应用频率及其分布研究

全面调查研究上海市开展X射线诊断的基本现状,并分别统计各种X射线诊断按照主要检查类型、受检者性别与年龄组分布的人次数,得出X射线诊断的医疗照射应用频率及其各类分布。截至2010年底,上海市拥有医疗卫生机构3 270家,其中开展X射线诊断业务的占39.11%。全市每千人口拥有执业(含助理)医师已达2.2人。"十一五"期间,数字摄影设备(DR)、计算机摄影设备(CR)、乳腺X射线摄影机、数字减影血管造影设备(DSA)分别以年均21.3%、13.5%、11.2%、10%的速度增长,普通X射线机却以年均8.1%的速度减少。2007年和2009年两年按人口加权的X射线诊断医疗照射应用年频率为763.23人次/千人口。以胸部检查、X-CT扫描检查、四肢及关节摄影等类型检查居多;头颅摄影、钡灌肠、骨盆及髋部摄影频率显著降低;而脊柱摄影、胆囊造影、躯干X-CT扫描检查和牙科全景摄影频率显著增加。0~15岁年龄组以胸部摄影居多,占56.66%;16~40岁年龄组胸部摄影和胸部透视分别各占22.54%和26.43%;大于40岁年龄组以胸部摄影和X-CT检查为主,分别各占32.19%和17.09%。显然,上海市"十一五"期间的X射线诊断应用频率已经达到历史新高,切实采取有力措施加强医疗照射防护是当前十分突出的重要公共卫生问题。     

微型X射线管金刚石光学窗口性能的模拟研究

以侧窗式微型X射线管为例,采用蒙特卡罗(Monte Carlo)方法,对金刚石光学窗口的最优厚度进行了模拟研究.以管压为50 kV、管电流为1.0 mA的X射线管工况为例的模拟结果表明:增加金刚石窗口厚度,可使银靶的Kα特征X射线有效透射比和峰总比不断提高;在最优厚度为2.0 mm的条件下,高能X射线有效透射比为154...     

数字化胸部X射线摄影中铜滤过对受检者辐射剂量的影响

采用西门子公司生产的数字化X射线透视摄影系统,在不同的附加铜滤过(0、0.1、0.2、0.3 mm)下,对不同厚度的聚甲基丙烯酸甲酯(PMMA)模体进行胸部摄影。利用对比度噪声比评估不同附加铜滤过对图像质量的影响,同时使用辐射剂量仪记录不同铜滤过下的体表入射剂量,以探讨数字化胸部X射线摄影中,附加铜滤过对受检者体表入射...     

碘化汞探测器的稳定性

低能光子与探测器物质的相互作用主要是光电效应。其光电吸收系数μ_(PE)是: μ_(PE)∝E_r~(-7/2)ρZ~5式中,E_4是入射射线能量(eV);ρ和z分别为探测器材料密度和原子序数。对低能X、γ射线探测,就必须考虑选择原子序数高、密度大的探测器材料。碘化汞作为低能光子探测器,基本满足上述要求。它的特点是:(1)原子序数高,对X射线有很好的阻止本领和相当高的灵敏度;(2)禁带宽度大,可在40℃以下温度范围内工作和保存;(3)体积小、重量轻、牢固可靠、可构成小型的便携式谱仪;(4)适用于低能(<100keV)X射线的探测,有很好的能量分辨率和能量线性,在核医学、X荧光分析、野外探测等方面有着广阔的应用前景。     

Complement of 99mTc-octreotide scintimammography to mammography in evaluating breast cancers

In this paper,the 99mTc-octreotide scintimammography as a useful complementary technique of mammography was evaluated in diagnosing breast cancers.The 45 breast lesions were consecutively detected by mammography,and 99mTc-octreotide scintimammography,and both combination technique on the basis of self-examination,physical examination.Clinical diagnosis was confirmed by histopathologic analysis.Radioactivity uptake ratios for tumor vs normal breast tissues (T/NT) were calculated using regions of interest.In the breast cancer groups and the benign lesion groups,the average uptake ratios of the 99mTc-octreotide were 1.63±0.19 and 1.09±0.13,respectively,and t was 9.638 (P0.001).Based on sensitivity,specificity,accuracy,positive predicting value,and negative predicting value,99mTc-octreotide scintimammography was 87%,79%,84%,90%,and 73%,the mammography was 65%,64%,64%,80%,and 45%,and both combination was 95%,100%,97%,100% and 92%,respectively.This showed that the 99mTc-octreotide scintimammography was more useful than mammography in the evaluating suspected breast cancers,and the combination technique can accurately discriminate lesions.     

Mammography and 99mTc-MIBI scintimammography in breast cancer diagnosis

The aim of this work has been to evaluate whether a diagnostic protocol based on the joint use of mammography and ^99mTc-MIBI scintimammography can help to distinguish the lesions and to reduce the number of biopsies required in patients with suspected breast cancer,A total of 58 women were evaluated by palpation ,mammography,scintimammography,Twenty-four patints were scintimammographed with ^99mTc-MIBI at 10 min after injection.Thirty-four patients were taken doublepase scintimammography with ^99mTc-MIBI 10min and 60-90 min fater injection. Based on mammography,the supicion degrees of malignancy were rated,and 30 results of malignancy were confirmed by histopatology,Based on mammography,18 lesion were considered to be most probably benign (of which 3 were histopathologically breast cancer),19 as indeterminate(of which 9 were histopatologically breast cancer),and 21 as malignant (of which 18 were histopathologically breast cancer),The results of early and delayed phases ^99mTc-MIBI scintimammography were the same.The sensitivity,specificity and accuracy of scintimammography were 74.29%,86.96% and 79.31%,respectively,Scintimammography gave 16 correct diagnosis in 19 mammogram indeterminate (84.2%) and demonstrated 5 out of 8 cases axillary lymph nodes metastasis (72.5%),These studies show that ^99mTc-MIBI scintimammography used as a complementary testing technique to mammography is useful in the examination of patients with suspected breast cancer,The adoption of a joint mammography-scintimammography diagnostic protocol could considerably reduce the number of biopsies performed in patients with lesion of indeterminate mammographic suspicion of malignancy.     

Multi-recycling in the ENHS and the equilibrium core

This work investigates the effect of initial fuel composition, power density and number of recycles on the pitch-to-diameter (P/D) ratio and TRans-Uranium isotopes (TRU) loading required for attaining one of the most important design goals of the Encapsulated Nuclear Heat Source (ENHS) – nearly zero burnup reactivity swing over the 20 years of core life. It is found that the required P/D ratio is sensitive to, primarily, the initial concentration of the short-lived isotope ²⁴¹Pu in the fuel loaded into the first core and to the core power density. The longer is the cooling time of the TRU from LWR spent fuel the smaller becomes the relative ²⁴¹Pu concentration and the smaller becomes the fraction of ²⁴¹Pu lost via radioactive decay and, hence, the smaller needs be the conversion ratio required for nearly zero burnup reactivity swing and the larger can be the P/D ratio. Likewise, the higher is the ENHS power density, the smaller becomes the fraction of ²⁴¹Pu lost via radioactive decay and the larger becomes the P/D required for the first core. The optimal P/D ratio tends to increase with the number of times the fuel is recycled from one ENHS core to the next one. The optimal P/D ratio for the equilibrium composition core is in between 1.53 and 1.59. For a given discharge burnup it tends to somewhat increase with the equilibrium core power density. However, if structural materials will be developed to enable a 20 years core life at elevated power densities, the higher the power density the smaller is the required equilibrium P/D ratio.     

Evaluation of some ratio effects in ^99mTc－MIBI imaging of breast tumors

The effectiveness of using some ratios in 99mTc-MIBI imaging fbr the diagnosis of breast tumors was evaluated. After 100 patients with the breast tumor underwent 99mTc-MIBI imaging, the ratios of tunor to contralateral uptake (T/N). tumor to heart uptake (T/H), and tumor to sternum uptake (T/S) were obtained and then analysed about their reproducibility and values in differentiating benign breast lesion the from malignant tumor. To detect breast cancers, the sensitivity, specificit y and accuracy of T/N were 92%, 90% and 91%, respectively. However, those of T/S were 70% (p ＜0.01), 74% (p ＜0.05), 72% (p ＜0.01), and those of T/H were 74%(p ＜0.05). 76% (p ＞0.05). 75% (p ＜0.01). The average coefticients of variation(CV) of T/N, T/S and T/H were 9.439±9.712. 4.856+4.420 (p ＞0.05), and 3.736±3.489 (p ＜0.05). It was found that T/N had the best sensitivity, specificity and accuracy todetect the breast cancer, but its reproducibility is poor. On the other hand, T/H has better reproducibility.     

Simulator performance upgrade and evaluation of loss of RHR during midloop operation for Maanshan PWR plant

Because a greater risk than expected is introduced during midloop operation for typical PWRs, the performance of training simulator of Taiwan’s Maanshan 3-loop PWR plant was verified and upgraded for midloop operation (MLO) simulation. Besides, plant specific midloop abnormal operation procedure (AOP) also was quantitatively evaluated. Instead of modifying existing RCS module, a thermal-hydraulic code, namely ROSE (Reactor Outage Simulation and Evaluation) has been developed and transplanted into the training simulator of Maanshan PWR plant. A two-region approach with a modified two-fluid model was adopted as the theoretical basis of the ROSE code. The success of the simulator performance upgrade for the MLO was demonstrated by comparisons to W-GOTHIC MLO calculation as well as the original simulator performance. Moreover, regarding the evaluation of the associated AOP for MLO after loss of RHR, the most risky plant configuration as well as associated crucial timing before core uncovery was also identified by the upgraded training simulator.     

Towards Quantification of Functional Breast Images Using Dedicated SPECT With Non-Traditional Acquisition Trajectories

Quantification of radiotracer uptake in breast lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g., scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect measurement of absolute tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800 mL breast with two lesion phantoms containing aqueous (99m)Tc pertechnetate were imaged using the SPECT sub-system of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30° tilted, and complex sinusoidal trajectories. Different energy windows around the photopeak were quantitatively compared, along with appropriate scatter energy windows, to determine the best quantification accuracy after attenuation and dual-window scatter correction. Measured activity concentrations in the reconstructed images for syringes with greater than 10 μCi /mL corresponded to within 10% of the actual dose calibrator measured activity concentration for ±4% and ±8% photopeak energy windows. The same energy windows yielded lesion quantification results within 10% in the breast phantom as well. Results for the more complete complex sinsusoidal trajectory are similar to the simple vertical axis acquisition, and additionally allows both anterior chest wall sampling, no image distortion, and reasonably accurate quantification.     

A note on the optimization of parameters for the design of a poison-tube tank

Computational analysis is carried out to arrive at the optimal parameters for the safe and economic design of a poison-tube tank for the storage of fissile solution. The parameters studied are tube diameter, gap between tubes, packed density of the neutron poison (Boron carbide) and wall thickness of the tubes. The aim is to maximize the fissile solution volume satisfying the safety criteria for criticality. Finding the precise values of optimal parameters is a very difficult task. Here a practical way of finding the optimal parameters subject to the design constraints is indicated.