共查询到19条相似文献,搜索用时 140 毫秒
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构建了内光源模型探讨散射介质中的光散射现象,利用蒙特卡罗方法研究了逃逸出组织的后向散射光子数随光子在组织内部发生的散射次数的分布关系,探讨了光源照明方式、辐射强度、接收方式、调制等参数的变化对后向散射的影响,结果表明后向散射光子的数量随散射次数的分布并非简单的单调递增或递减,而是一条先增大后减小出现峰值的曲线. 峰值位置、峰值大小及曲线形状与光源、探测方式、组织光学特性参数等有关.
关键词:
医用光学与生物技术
散射介质
后向散射
蒙特卡罗模拟 相似文献
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X射线在影象增强器中背向散射特性的研究 总被引:1,自引:0,他引:1
本文用蒙特卡罗方法模拟了轫致辐射X射线在影象增强器中的背向散射特性。针对X线源管电压为30-120kV的轨致辐射入射,给出了背向散射光子的角分布及能谱分布;同时,还给出了背向散射光子的平均能量和平均出射角与管电压的关系以及吸收光子数和直透光子数与管电压的关系。 相似文献
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纺织纤维的光散射特性在纺织材料微观结构、光学性质以及无损检测中至关重要。利用纺织纤维各向异性的结构特点改进现有的角谱展开法,得到纺织纤维对倾斜入射平面波的散射以及表征其光散射特性的Mueller矩阵。采用蒙特卡罗算法模拟了平行棉纤维束对倾斜入射偏振光的多次散射,并对其计算结果进行了实验验证。结果表明理论计算和实验测量的散射光斑在形状特征、光强分布上均一致,从而验证了蒙特卡洛方法模拟纺织纤维光散射的正确性。结果同时也表明蒙特卡罗方法在纺织材料光传播特性的理论研究中具有重要的指导意义。 相似文献
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设计了一系列实验对Concorde MicroPET Rodent R4小动物正电子断层成像系统(该系统是Concorde Microsystems公司开发的小动物专用PET扫描仪,该扫描仪具有32层探测器环,动物入口孔径为120mm,横向视野为100mm,轴向深度为78mm,标称的视野中央处的空间分辨率可达1.8mm以下)的空间分辨率、灵敏度、散射率等性能参数进行了测试,测试结果显示该扫描仪视野中心的横向空间分辨率为1.9mm, 轴向空间分辨率为1.88mm, 在能窗设定为250—750keV时系统的绝对灵敏度为39.88 cps/kBq, 同样能窗下二维重建散射分数为50.6%,三维重建散射分数为32.3%.
关键词:
正电子断层成像仪
性能测试 相似文献
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给出了一种结合射线追踪和蒙特卡罗方法计算含核粒子光散射的方法,内核粒子可以为稀疏分布也可为浓密分布.粒子外边界的反射和折射由射线追踪方法计算,而粒子内部的多次散射过程由蒙特卡罗方法模拟;当内核粒子为浓密随机分布时,其单次散射特性由基于静态结构因子(static structure factor)的浓密介质光散射理论计算.最后讨论了含核椭球粒子模型的单次散射特性.
关键词:
射线追踪技术
蒙特卡洛方法
光散射
椭球粒子 相似文献
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给出一种基于康普顿散射理论的Tl-201 SPECT影像的散射校正方法,此方法仅考虑一次散射和二次散射的影响.计算中将散射介质分成散射小元,然后积分求出每一小元内所有电子的散射光子数,一个电子的散射几率由Klein-Nishina公式确定,散射光子被分配至散射小元中心对应的探测器接收孔位置.辐射源的奇点问题也通过这种积分方法解决.误差主要来自于计算中有限的散射元体积和受限制的散射介质,但计算的线源响应函数和散射比与Monte Carlo计算结果相符,计算时间缩短40倍. 相似文献
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An effective scatter correction method based on single scatter simulation for a 3D whole-body PET scanner 下载免费PDF全文
Hamamatsu SHR74000 is a newly designed full three-dimensional (3D) whole body
positron emission tomography (PET)
scanner with small crystal size and large field of view (FOV). With
the improvement of sensitivity, the scatter events increase
significantly at the same time, especially for large objects.
Monte Carlo simulations help us to understand the scatter phenomena and
provide good references for scatter correction. In this paper, we
introduce an effective scatter correction method based on single
scatter simulation for the new PET scanner, which accounts for the
full 3D scatter correction. With the results from Monte Carlo
simulations, we implement a new scale method with special
concentration on scatter events from outside the axial FOV and
multiple scatter events. The effects of scatter correction are
investigated and evaluated by phantom experiments; the results
show good improvements in quantitative accuracy and
contrast of the images, even for large objects. 相似文献
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为了快速模拟高能质子照相过程,利用蒙特卡罗(MC)技术和技巧编写了程序QMCPrad,并开展了QMCPrad与MCNPX的对比计算以及实验E955的模拟验证工作。在模型选取中,修改核反应过程权重的隐式俘获模式和一次抽样模拟穿透客体的多次库仑散射的浓缩历史方式都节约了大量的计算时间。与MCNPX相比,QMCPrad具备模拟质子在磁透镜中输运过程的能力。QMCPrad与MCNPX、实验E955的对比及验证结果表明,QMCPrad能够准确定量地模拟高能质子照相,为质子照相实验设计提供工具。 相似文献
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SHR22000是日本滨松光子学株式会社开发的人体全身用正电子发射断层扫描仪. 扫描仪具有32层探测器环, 二维采集可形成63个切片, 病人孔径为60cm, 单个体位数据采集时间为3—5min.扫描仪的轴向视野为22.5cm, 经5个体位可以完成全身扫描, 视野中轴10mm处平均横向分辨率可达到3.2mm. 本文依照国际标准IEC 61675-1(亦即GB/T18988.1-2003)规定的各项指标对该扫描仪的空间分辨率、灵敏度、散射和计数率特性以及复原系数进行了测试, 并给出结果数据. 相似文献
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The authors propose a combined scatter reduction and correction method to improve image quality in cone beam computed tomography (CBCT). The scatter kernel superposition (SKS) method has been used occasionally in previous studies. However, this method differs in that a scatter detecting blocker (SDB) was used between the X-ray source and the tested object to model the self-adaptive scatter kernel. This study first evaluates the scatter kernel parameters using the SDB, and then isolates the scatter distribution based on the SKS. The quality of image can be improved by removing the scatter distribution. The results show that the method can effectively reduce the scatter artifacts, and increase the image quality. Our approach increases the image contrast and reduces the magnitude of cupping. The accuracy of the SKS technique can be significantly improved in our method by using a self-adaptive scatter kernel. This method is computationally efficient, easy to implement, and provides scatter correction using a single scan acquisition. 相似文献
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《中国物理C(英文版)》2017,(4)
This work investigates the positional single photon incidence response(P-SPIR) to provide an accurate point spread function(PSF)-contained system matrix and its incorporation within the image reconstruction framework.Based on the Geant4 Application for Emission Tomography(GATE) simulation,P-SPIR theory takes both incidence angle and incidence position of the gamma photon into account during crystal subdivision,instead of only taking the former into account,as in single photon incidence response(SPIR).The response distribution obtained in this fashion was validated using Monte Carlo simulations.In addition,two-block penetration and normalization of the response probability are introduced to improve the accuracy of the PSF.With the incorporation of the PSF,the homogenization model is then analyzed to calculate the spread distribution of each line-of-response(LOR).A primate PET scanner,Eplus-260,developed by the Institute of High Energy Physics,Chinese Academy of Sciences(IHEP),was employed to evaluate the proposed method.The reconstructed images indicate that the P-SPIR method can effectively mitigate the depth-of-interaction(DOI) effect,especially at the peripheral area of field-of-view(FOV).Furthermore,the method can be applied to PET scanners with any other structures and list-mode data format with high flexibility and efficiency. 相似文献
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遗传算法在散射介质光输运逆问题研究中的应用 总被引:2,自引:0,他引:2
建立了一个散射介质模型,在用蒙特卡罗方法成功模拟介质中光输运过程的基础上,用遗传算法有效地解决了因蒙特卡罗方法模拟结果的离散性和统计性使其在利用传统化方法进行逆问题研究时存在的困难,从而较好地实现了对散射介质模型的单个光学特性参数的重构和多参数的联合重构,同时还深入地讨论了遗传算法在过程中的作用机理。 相似文献
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In biological suspensions, the forward light scattering is done mainly by the contribution of the suspended cells. The multiple scattering is almost always unavoidable, its contribution being described by Monte Carlo simulations or by approximate analytical formula. The Monte Carlo approach we propose moves one photon at a time and checks all scattering centers to find, at each simulation step, which one will scatter the photon. The validation of the simulation results is performed by comparing the obtained angular distribution with the predictions of the effective phase function theory reported recently in the literature and with the angle resolved experimental measurements performed on human red blood cells (RBCs) in suspensions at different hematocrits. The results show a good agreement in the small concentration range. 相似文献
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In this paper, we investigate the performance of a cylindrical positron emission mammography (PEM) by simulation, in order to estimate its feasibility before implementation. A well-developed simulation package, Geant4 Application for Tomographic Emission (GATE), is used to simulate the scanner geometry and physical processes. The simulated PEM scanner is composed of 64 blocks axially arranged in 4 rings with an axial field-of-view (AFOV) of 12.8 cm and 16.6 cm in diameter. For each block, there is a 16×16 array of 2 mm×2 mm×15 mm lutetium yttrium oxyorthosilicate (LYSO) crystals. In the simulated measurements, the spatial resolution is at the center of the FOV of 1.73±0.07 mm (radial) and 1.81±0.08 mm (tangential), but of 4.83±0.09 mm (radial) and 4.37±0.07 mm (tangential) while 5 cm off the center. The central point source sensitivity (ACS) is 4.04% (1.50 Mcps/mCi) at an energy window of 350-650 keV. Moreover, the capillary and cylindrical sources are simulated coupled to breast phantoms for the scatter fraction (SF) and Noise Equivalent Count Rate (NECR) test. For a breast phantom with a 350-650 keV energy window, SF may reach the highest 32.95%, while NECR is degraded down to the lowest 255.71 kcps/mCi. Finally, we model a breast phantom embedded with two spheres of different activities. The reconstructed image gives good results despite a bit of difference in image contrast. Further, the image quality will be improved by scatter and random correction. All these test results indicate the feasibility of this PEM system for breast cancer detection. 相似文献