目的基于线性模型的双能CT(Dual-Energy CT,DECT)测量相对电子密度(Relative Electron Density,RED)被证明在方法学上是可行的。体模在其中的作用是确定模型的系数。本研究的目的是提出一种专用于DECT模拟的体模原型。方法采用碘为光电...目的基于线性模型的双能CT(Dual-Energy CT,DECT)测量相对电子密度(Relative Electron Density,RED)被证明在方法学上是可行的。体模在其中的作用是确定模型的系数。本研究的目的是提出一种专用于DECT模拟的体模原型。方法采用碘为光电吸收基质,水和乙醇为康普顿散射基质,分别配制浓度不同的溶液,封装并置于CIRS 062体模的插孔中,在Siemens SOMATOM CT扫描仪上,采用上腹部常用协议进行双能扫描,管电压为80 k Vp/Sn和140 k Vp/Sn。分析高低能量图像减权算子与RED的关系。结果自制体模和CIRS 062体模实验所确定的拟合直线的可决系数均大于0.99,电子密度测量误差分别为1.75%和1.31%。把其中一组实验确定的线性模型用于另一组实验,RED测量误差无显著差别。结论 DECT测量电子密度的体模无需模拟特定组织,自制体模可代替组织等效体模确定Saito线性模型的系数。展开更多
背景与目的:肿瘤部位的精准放疗取决于治疗靶区精准的剂量分布,探究使用不同计算机体层成像值-相对电子密度(computed tomography value to the relative electron density,CT-RED)校准曲线对计算各部位肿瘤剂量分布的影响,同时探索拟...背景与目的:肿瘤部位的精准放疗取决于治疗靶区精准的剂量分布,探究使用不同计算机体层成像值-相对电子密度(computed tomography value to the relative electron density,CT-RED)校准曲线对计算各部位肿瘤剂量分布的影响,同时探索拟合一条CT-RED校准曲线的方法。方法:使用复旦大学附属肿瘤医院的两台CT定位机分别对CIRS-062型电子密度模体扫描,获得两组不同部位(头、胸、腹)临床扫描协议的CT-RED校准曲线,并综合各曲线优化出一条改良CT-RED曲线。使用原始及改良CT-RED曲线在治疗计划系统(treatment planning system,TPS)中分别计算各病例计划靶区(planning target volume,PTV)(鼻咽癌、肺癌和宫颈癌各16例)和危及器官(organ at risk,OAR)的剂量分布。最后在各肿瘤中选取5例来验证改良CT-RED曲线的可行性。结果:采用不同校准曲线计算出的剂量在腹部和头颈部中差异较小(<1.00%和<1.13%),但在肺部低密度区域有较大差异(2.50%);使用改良CT-RED曲线与标准CT-RED曲线分别计算头、胸和腹部肿瘤获得的剂量分布无显著差异(<1.00%)。结论:计算不同部位肿瘤的剂量分布应选取对应的CT-RED校准曲线。在具有多台CT定位机的中心也可选择改良CT-RED校准曲线方案以降低选错校准曲线的潜在风险。展开更多
Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond we...Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond were successfully prepared by spark plasma sintering（SPS） method. The sintering temperatures and volume fractions（50%, 60% and 70%） of diamond were changed to investigate their effects on the relative density, homogeneity of the microstructure and thermal conductivity of the composites. The results show that the relative density, homogeneity of the microstructure and thermal conductivity of the composites increase with decreasing the diamond volume fraction; the relative density and thermal conductivity of the composites increase with increasing the sintering temperature. The thermal conductivity of the composites is a result of the combined effect of the volume fraction of diamond, the homogeneity and relative density of the composites.展开更多
We have quantitatively investigated the radiation belt's dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)...We have quantitatively investigated the radiation belt's dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)-driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the Radiation Belt Content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions, radial diffusion, and adiabatic transport. Due to the limitation of numerical schemes, formal radiation belt models do not include the cross diffusion term of local wave-particle interactions. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders (depending on the pitch angle) if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field; the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model, which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere; the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell (the outer magnetosphere); in smaller L shell regions (the inner magnetosphere), the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.展开更多
文摘目的基于线性模型的双能CT(Dual-Energy CT,DECT)测量相对电子密度(Relative Electron Density,RED)被证明在方法学上是可行的。体模在其中的作用是确定模型的系数。本研究的目的是提出一种专用于DECT模拟的体模原型。方法采用碘为光电吸收基质,水和乙醇为康普顿散射基质,分别配制浓度不同的溶液,封装并置于CIRS 062体模的插孔中,在Siemens SOMATOM CT扫描仪上,采用上腹部常用协议进行双能扫描,管电压为80 k Vp/Sn和140 k Vp/Sn。分析高低能量图像减权算子与RED的关系。结果自制体模和CIRS 062体模实验所确定的拟合直线的可决系数均大于0.99,电子密度测量误差分别为1.75%和1.31%。把其中一组实验确定的线性模型用于另一组实验,RED测量误差无显著差别。结论 DECT测量电子密度的体模无需模拟特定组织,自制体模可代替组织等效体模确定Saito线性模型的系数。
文摘背景与目的:肿瘤部位的精准放疗取决于治疗靶区精准的剂量分布,探究使用不同计算机体层成像值-相对电子密度(computed tomography value to the relative electron density,CT-RED)校准曲线对计算各部位肿瘤剂量分布的影响,同时探索拟合一条CT-RED校准曲线的方法。方法:使用复旦大学附属肿瘤医院的两台CT定位机分别对CIRS-062型电子密度模体扫描,获得两组不同部位(头、胸、腹)临床扫描协议的CT-RED校准曲线,并综合各曲线优化出一条改良CT-RED曲线。使用原始及改良CT-RED曲线在治疗计划系统(treatment planning system,TPS)中分别计算各病例计划靶区(planning target volume,PTV)(鼻咽癌、肺癌和宫颈癌各16例)和危及器官(organ at risk,OAR)的剂量分布。最后在各肿瘤中选取5例来验证改良CT-RED曲线的可行性。结果:采用不同校准曲线计算出的剂量在腹部和头颈部中差异较小(<1.00%和<1.13%),但在肺部低密度区域有较大差异(2.50%);使用改良CT-RED曲线与标准CT-RED曲线分别计算头、胸和腹部肿瘤获得的剂量分布无显著差异(<1.00%)。结论:计算不同部位肿瘤的剂量分布应选取对应的CT-RED校准曲线。在具有多台CT定位机的中心也可选择改良CT-RED校准曲线方案以降低选错校准曲线的潜在风险。
文摘Cu/diamond composites have been considered as the next generation of thermal management material for electronic packages and heat sinks applications. Cu/diamond composites with different volume fractions of diamond were successfully prepared by spark plasma sintering（SPS） method. The sintering temperatures and volume fractions（50%, 60% and 70%） of diamond were changed to investigate their effects on the relative density, homogeneity of the microstructure and thermal conductivity of the composites. The results show that the relative density, homogeneity of the microstructure and thermal conductivity of the composites increase with decreasing the diamond volume fraction; the relative density and thermal conductivity of the composites increase with increasing the sintering temperature. The thermal conductivity of the composites is a result of the combined effect of the volume fraction of diamond, the homogeneity and relative density of the composites.
文摘目的探讨CT设备的扫描电压对常规放疗计划系统在靶区剂量计算影响的研究.方法用已知的电子密度CIRS062模体,在64排CT上扫描两组CT图像电压分别为120KV及140KV,建立两组CT-相对电子密度曲线(computed tomography number-relative electron density,CT-RED)并进行分析.选择临床病例24例,乳腺癌、宫颈癌及骨转移各8例.每个临床病例分别用上述两种CT-RED曲线进行两次计划设计,计划设计的处方剂量及函数等参数保持一致,比较计划剂量计算的结果差异.结果CT-RED曲线的CT值均随着材料电子密度的增大而增大;电子密度在0~1.117之间CT值差异非常小,电子密度在1.117及以上的区间,两条曲线CT值差异越来越大.在计划中乳腺癌、骨转移及宫颈癌患者PTV的Dmean及机器跳数均有不同程度的差异,其中在电子密度较大的骨转移靶区剂量差异较大,但统计学并无显著差异(P>0.05).结论在常用的CT扫描电压下对人体范围之内的电子密度常规计划靶区剂量并无显著影响的.
基金supported by the National Basic Research Program of China (Grant No. 2012CB825603)the Specialized Research Fund for State Key Laboratories
文摘We have quantitatively investigated the radiation belt's dynamic variations of 1.5-6.0 MeV electrons during 54 CME (coronal mass ejection)-driven storms from 1993 to 2003 and 26 CIR (corotating interaction region)-driven recurrent storms in 1995 by utilizing case and statistical studies based on the data from the SAMPEX satellite. It is found that the boundaries determined by fitting an exponential to the flux as a function of L shell obtained in this study agree with the observed outer and inner boundaries of the outer radiation belt. Furthermore, we have constructed the Radiation Belt Content (RBC) index by integrating the number density of electrons between those inner and outer boundaries. According to the ratio of the maximum RBC index during the recovery phase to the pre-storm average RBC index, we conclude that CME-driven storms produce more relativistic electrons than CIR-driven storms in the entire outer radiation belt, although the relativistic electron fluxes during CIR-related storms are much higher than those during CME-related storms at geosynchronous orbit. The physical radiation belt model STEERB is based on the three-dimensional Fokker-Planck equation and includes the physical processes of local wave-particle interactions, radial diffusion, and adiabatic transport. Due to the limitation of numerical schemes, formal radiation belt models do not include the cross diffusion term of local wave-particle interactions. The numerical experiments of STEERB have shown that the energetic electron fluxes can be overestimated by a factor of 5 or even several orders (depending on the pitch angle) if the cross diffusion term is ignored. This implies that the cross diffusion term is indispensable for the evaluation of radiation belt electron fluxes. Formal radiation belt models often adopt dipole magnetic field; the time varying Hilmer-Voigt geomagnetic field was adopted by the STEERB model, which self-consistently included the adiabatic transport process. The test simulations clearly indicate that the adiabatic process can significantly affect the evolution of radiation belt electrons. The interactions between interplanetary shocks and magnetosphere can excite ULF waves in the inner magnetosphere; the excited polodial mode ULF wave can cause the fast acceleration of "killer electrons". The acceleration mechanism of energetic electrons by poloidal and toroidal mode ULF wave is different at different L shells. The acceleration of energetic electrons by the toroidal mode ULF waves becomes important in the region with a larger L shell (the outer magnetosphere); in smaller L shell regions (the inner magnetosphere), the poloidal mode ULF becomes responsible for the acceleration of energetic electrons.
