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121.
针孔单光子发射计算机断层(SPECT)成像的空间分辨率通常是根据Anger经验公式来进行估算,与实际测量存在较大偏差.本文通过对针孔成像的物理过程进行分析,提出了一个近似度更高的计算公式.利用精确的蒙特卡罗方法模拟针孔SPECT成像,采用OSEM(ordered subsets expectation maximization)算法对投影数据进行图像重建,并与模具实验进行比较,验证了理论公式的适用性.同时还讨论了体素尺寸、几何映射获取投影矩阵以及探测器尺寸与成像物体尺寸比值对断层图像空间分辨率的影响.实验结果显示,该理论公式所估算的空间分辨率比实验值平均偏小约10%,而Anger经验公式所估算的空间分辨率比实验值平均偏大约60%.因此,该理论公式能更好地估算针孔SPECT成像的空间分辨率,可为针孔SPECT系统的设计和使用提供有价值的参考. 相似文献
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124.
OCT图像法测量折射率 总被引:2,自引:0,他引:2
基于光程匹配原理提出了一种用光学相干断层成像(OCT)系统获得的图像测量样品折射率的方法。通过分析光程匹配原理,给出用OCT图像法测量样品折射率的原理及过程。以玻璃载波片和黄瓜组织为样品进行实验。实验结果表明,用OCT图像法获得的载玻片和黄瓜组织的折射率测量值分别为1.499和1.353,与发表或已知的折射率结果相吻合,测试结果的随机误差可小于0.01。另外,使用OCT图像法通过短时间所采集的两幅图像可对横向扫描任意位置的折射率同时进行测量。该方法进一步简化了基于光程匹配原理的折射率测量法的过程,缩短了测量时间,是一种快速测量样品折射率的实用方法。 相似文献
125.
介绍了一种正电子发射断层成像术实时查找表电路。该电路接收符合电路输出的位置信号和能量信号,用查表的方法完成重心法中的除法运算,然后再第二次查表得到该γ光子所入射到的晶格的离散化坐标值和能量阈值,并完成能量甄别以剔除部分散射事件。此外,该电路还结合了呼吸门控和心电门控功能。查找表存储在flash器件中,由CPLD控制读写。本设计的特点是利用硬件电路来完成查找表功能,效率更高,每次事件的查表寻址的延迟时间小于100ns,并且可以在线更新查找表的内容,使用方便。另外,还说明了用CPLD来读写NORflash的方法,以及该电路与系统中其它模块间的数据通信方法。 相似文献
126.
<正>With the development of the compressive sensing theory,the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology.This paper develops an iterative algorithm for image reconstruction,which can fit most cases.This method gives an image reconstruction flow with the difference image vector,which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough.Then the l_2-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles.The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data.Moreover,all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed. 相似文献
127.
γ+jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies.Tagging events with a well identified high p T direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon in ALICE,allows us to determine,with a good approximation,both the jet fragmentation function and the back-to-back azimuthal alignment of the direct photon and the jet.Comparing these two observables measured in pp collisions with the ones measured in AA collisions will reveal the modifications of the jet structure induced by the medium formed in AA collisions and consequently will infer the medium properties. 相似文献
128.
In range-resolved reflective tomography laser radar imaging system, for accurate image reconstruction, all projections must be aligned to the center of target rotation. Due to the unknown location of the axis of rotation and random target translation, the center of target rotation in each projection cannot be measured accurately and images reconstructed based on range-resolved projections without registration would be dislocated. Here, we apply a feature tracking method to align projections data for tomographic reconstruction in laboratory-scale laser radar imaging. The target was placed on a spin table with an unknown and fixed axis, and the oscillatory motion of the target translation was simulated by a second order inertia filter to accord with the real satellites vibrations. The experimental simulation results demonstrate the effectiveness of this method to improve images reconstruction equality. The application of this method to actual radar imaging in remote distance was discussed and the differences were compared with the lab setups. 相似文献
129.
We propose a new system of an extremely narrow light pulse generation for optical microscopy applications using a nonlinear ring resonator system. The system consists of one nano and three micro-optical ring resonators, which can be used to generate the 50 fm (10−15 m) optical spectral width at the broad wavelength spectrum. By using a soliton pulse with a pulse width of 50 ps, peak power of 1 W, center wavelength at 550 nm, and after the soliton pulse is launched into the first ring device, the chaotic pulses are generated within the first ring. The chaotic filtering behaviors are performed by using the second and the third ring devices, whereas the extremely short pulse, i.e. narrow spectral width, can be generated by using the extended nano-ring device. The broad spectrum of the harmonic waves is generated and filtered, which is of use in optical tomography. Results obtained have shown that the generation of the broad spectrum of short pulse with width 100 fm and peak power 60 mW is achieved. The possibility of using such a system for nondestructive bio-cells microscopy, for visualizing bio-cells and for bio-cells tomography is also discussed in detail. 相似文献
130.
Elie Nasr 《计算数学(英文版)》2010,(3):401-417
We present a new iterative reconstruction algorithm to improve the algebraic reconstruction technique (ART) for the Single-Photon Emission Computed Tomography. Our method is a generalization of the Kaczmarz iterative algorithm for solving linear systems of equations and introduces exact and implicit attenuation correction derived from the attenuated Radon transform operator at each step of the algorithm. The performances of the presented algorithm have been tested upon various numerical experiments in presence of both strongly non-uniform attenuation and incomplete measurements data. We also tested the ability of our algorithm to handle moderate noisy data. Simulation studies demonstrate that the proposed method has a significant improvement in the quality of reconstructed images over ART. Moreover, convergence speed was improved and stability was established, facing noisy data, once we incorporate filtration procedure in our algorithm. 相似文献