共查询到20条相似文献,搜索用时 31 毫秒
1.
Yuasa T. Akiba M. Takeda T. Kazama M. Hoshino A. Watanabe Y. Hyodo K. Dilmanian F.A. Akatsuka T. Itai Y. 《IEEE transactions on nuclear science》1997,44(1):54-62
We describe a new attenuation correction method for fluorescent X-ray computed tomography (FXCT) applied to image nonradioactive contrast materials in vivo. The principle of the FXCT imaging is that of computed tomography of the first generation. Using monochromatized synchrotron radiation from the BLNE-5A bending-magnet beam line of Tristan Accumulation Ring in KEK, Japan, we studied phantoms with the FXCT method, and we succeeded in delineating a 4-mm-diameter channel filled with a 500 μg I/ml iodine solution in a 20-mm-diameter acrylic cylindrical phantom. However, to detect smaller iodine concentrations, attenuation correction is needed. We present a correction method based on the equation representing the measurement process. The discretized equation system is solved by the least-squares method using the singular value decomposition. The attenuation correction method is applied to the projections by the Monte Carlo simulation and the experiment to confirm its effectiveness 相似文献
2.
A high energy X-ray computed tomography (CT) system with an electron linear accelerator was developed to image cross-sections of large-scale and high-density materials. An electron linear accelerator is used as the X-ray source. The maximum X-ray energy is 12 MeV, and the average energy is around 4 MeV. The intensity of the X-ray fan beam passing through the test object is measured by a 15-channel detector array. CWO (CdWO4) scintillators and photodiodes are used as the X-ray detectors. The crosstalk noise due to scattering of X-ray photons by adjacent detectors is reduced to less than 1.6% by installing tungsten shields between the scintillators. Extra channels are used to compensate for base line shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-rays transmitted in a 420-mm thick iron block. A spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter 相似文献
3.
Polychromatic L-shell X-ray fluorescence computed tomography is a promising imaging technique to explore the element distribution of the sample. However, the image quality of large samples would be decreased dramatically due to the present of the self-absorption. In this investigation, an attenuation correction algorithm based on theories related to X-ray fluorescence was proposed. With this method, the attenuation coefficients at the incident energies were expressed as a function of known X-ray energies and unknown platinum concentrations. Then the attenuation coefficients were calculated based on the theories and added in the contribution value of the pixel in Maximum Likelihood Expectation Maximization reconstruction method. The element distributions can be got through continuous iterations. Finally, the feasibility of this method was tested by Monte Carlo simulation. The results indicated that, for a 4-mm diameter phantom containing an object of 2 mm in diameter with 0.10 wt% platinum solutions, the CNR of reconstructed images increased from 53.5 to 203.8 after attenuation correction while the relative error decreases from 97% to 2%. 相似文献
4.
T. Mitsutake S. Morooka K. Suzuki S. Tsunoyama K. Yoshimura 《Nuclear Engineering and Design》1990,120(2-3):203-212
An interfacial shear stress equation in the dispersed-annular two-phase flow regime has been developed, which is based on a three-fluid model consisting of a liquid film on a rod, vapor and entrained liquid associated with a vapor flow. It is an extension of J.G.M. Andersen's procedure that provides a two-fluid interfacial shear stress equation using the drift flux parameters C0 and Vgj. This interfacial shear stress equation can take into account a phase and velocity distribution through an equivalence between the drift flux parameters and the interfacial shear stress.
Using the three-fluid subchannel analysis code TEMPO with the three-fluid interfacial shear stress model, the capability of a three-fluid calculation using the drift flux parameters C0 and Vgj that reproduce a measured void fraction is demonstrated. A comparison was made with advanced X-ray computed tomography (CT) void fraction data within a 4×4 rod bundle in diabatic 1 MPa pressure conditions. The three-fluid velocity field was estimated to be in good agreement with the experimental result of a void fraction. 相似文献
5.
A general beam-hardening correction technique is presented. Knowledge of the CT (computerized tomography) scanner X-ray spectrum is necessary. This postreconstruction method does not require the original projection data. Simulated projections through an uncorrected reconstructed image are used to correct for beam hardening. Errors in the mean linear attenuation coefficient are decreased from 30% to 5% with virtual elimination of the visual streaking artifact. The theoretical image improvement equals that of projection linearization postreconstruction methods using the original projection data. The correction is limited to cases where the material causing the beam hardening is contained within the reconstruction space 相似文献
6.
针对未知样品能量色散X射线荧光分析(energy dispersive X-ray fluorescence analysis, EDXRFA)方法开展无标样分析,通过测量Ti、Fe、Ni、Cu、Zn、Sr、Sn、Pb单元素标样,得到Rh靶材原级谱中Kα峰的相干与非相干散射峰强度比值R,并建立R与对应单元素标样有效原子序数的关系,得到Zeff-R的拟合曲线。求解未知样品基体时,测量未知样,得到其R,将R代入Zeff-R拟合曲线得到未知样有效原子序数,再通过基本参数法迭代计算其质量衰减系数。利用Ti、Fe、Ni、Cu、Zn、Sr、Sn、Pb单元素标样刻度仪器获取Gi参数,求解未知样品基体时用于相应元素的基本参数迭代。为验证算法可靠性,采用本算法分析15个国家土壤标准样品,结果表明,Ti、Fe、Ni、Cu、Zn元素的计算含量与标准含量接近,部分低含量元素受到散射本底等因素影响,含量误差较大。结果表明,该方法能够用于现场能量色散X射线荧光分析。 相似文献
7.
X射线CT中,X射束硬化导致重建图像中出现伪影,严重影响了图像质量。论文深入分析了射束硬化对原始投影数据的影响,并提出了一种基于基图像TV模型的射束硬化校正方法。该方法首先依据射束硬化的物理特征建立了带有可调参数的初步校正模型;其次,在不同的可调参数条件下,原始投影数据经该模型预处理变换得到多组预处理投影序列;再次,分别对预处理投影序列进行重建得到一系列校正基图像;最后,将基图像的线性组合作为最终重建图像。其中,加权系数的最优解是以最终重建图像的全变分(Total Variation,TV)函数作为目标函数,通过迭代法求得。为验证该算法,对真实的铝柱体模和工业检测件进行了实验,结果表明,该算法对射束硬化引起的杯状和条状伪影均有显著的抑制效果。 相似文献
8.
Y. K. Ng I. Orlic S. C. Liew K. K. Loh S. M. Tang T. Osipowicz F. Watt 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1997,130(1-4):109-112
A new approach for PIXE tomography has recently been introduced by our group. The reconstruction program is based on the maximum likelihood expectation maximization (MLEM) algorithm. Since the algorithm is built upon the actual stochastic model of X-ray production and propagation, attenuation correction as well as ion energy loss are readily incorporated into the reconstruction. The resultant procedures have been previously tested by using simulated X-ray yields and the results were given in an earlier paper. In this work, we present the results of the tomographic reconstruction of a realistic sample done in order to study the effectiveness of the algorithm. 相似文献
9.
Naruse Y. Kobayashi T. Jimbo M. Tanoue T. Suzuki T. 《IEEE transactions on nuclear science》1981,28(1):47-49
Prototype 200 channel semiconductor detectors for third generation X-ray computed tomography have been developed using surface-barrier diodes fabricated from high-purity n-type silicon. The image reconstruction test was successful, and the relationship between the image quality and the detector characteristics has been studied. 相似文献
10.
Yoshihiro Maruyama Takumi Hamaguchi Tien-Hsiu Tsai 《Journal of Nuclear Science and Technology》2018,55(2):199-208
A new ‘transXend’ detector system has been developed for energy-resolved computed tomography (CT). It consists of several segmented detectors that measure X-rays as electric currents. Response functions of segmented detectors are estimated using component materials of a body under inspection to unfold X-ray spectra. To avoid material-dependent measurements, response functions inherent to segmented detectors are evaluated by Monte Carlo calculations. CT was performed for a phantom consisting of five resins and was analyzed by the estimated response functions. The linear attenuation coefficients for the five resins have excellent agreement with database values. 相似文献
11.
《核技术(英文版)》2016,(3):9-19
A precise knowledge of geometry is always pivotal to a 3-D X-ray imaging system,such as computed tomography(CT),digital X-ray tomosynthesis,and computed laminography.To get an accurate and reliable reconstruction image,exact knowledge of geometry is indispensable.Nowadays,geometric calibration has become a necessary step after completing CT system installation.Various geometric calibration methods have been reported with the fast development of 3-D X-ray imaging techniques.In these methods,different measuring methods,calibration phantoms or markers,and calculation algorithms were involved with their respective advantages and disadvantages.This paper reviews the history and current state of geometric calibration methods for different3-D X-ray imaging systems.Various calibration algorithms are presented and summarized,followed by our discussion and outlook. 相似文献
12.
Determination of L3 subshell X-ray production cross-sections and fluorescence yields of Pb, Th and U
nder
im
ek 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2000,170(3-4):293-298
A study of L3 subshell X-ray production cross-sections and fluorescence yields by using characteristic K X-rays as the exciting radiation is described. Only the L3 subshells of Pb, Th and U were excited by the characteristic K X-rays of the elements used as secondary sources. The cross-sections for the production of Ll, L and Lβ groups of L3 subshell X-rays of Pb, Th and U have been measured using photoionization by Rb, Nb and Mo K X-rays. The measured L3 X-ray production cross-section values for Pb, Th and U are in good agreement with the theoretical ones evaluated using L3 subshell fluorescence yield ω3, fractions of the radiative width F3i and L3 subshell photoionization cross-section σ3. The L3 subshell fluorescence yields (ω3) have also been computed using the presently measured cross-section values and the theoretical L3 subshell photoionization cross-section values. These results are compared with the theoretically predicted values. 相似文献
13.
V. Rusanov Sv. Stankov V. Angelov V. Schünemann 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2000,170(3-4):443-453
The Mössbauer line broadening method for the determination of Lamb–Mössbauer factors fLM cannot be applied directly in the determination of the probability of the resonant absorption fLM for single-crystalline absorbers with quadrupole splitted Mössbauer spectra. The line width Γexp for single crystals with quadrupole splitted Mössbauer spectra has been computed for various absorber thicknesses. The polarization effects are important and have been taken into account. The linear dependence has been adapted for Lamb–Mössbauer factor measurements by introducing a polarization-dependent coefficient. This method has been tested on measurements of guanidinium nitroprusside (GNP) (CN3H6)2[Fe(CN)5NO] single crystals. 相似文献
14.
《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1999,150(1-4):18-26
L1,2, Lβ1,3,4, Lβ2,15, Lγ1(5) and Lγ2,3(4,4′) X-ray production cross-sections have been measured on selected medium-Z elements using 16O ions with energies from 0.19 to 0.75 MeV u−1. Calculated L-subshell ionization cross-sections were compared with the predictions of the direct ionization theories: the ECPSSR theory, the semiclassical approximation (SCA) in the united atom limit (SCA-UA) and SCA coupled-channel calculations (SCA-CC) involving a few lowest lying states. For the ECPSSR theory, large discrepancies were found for all three subshells. Better overall agreement between the experiment and theory was found for the SCA-UA theory. SCA-CC calculations improved the agreement between experiment and theory for the L2-subshell in the very adiabatic region. By measuring the L X-ray production cross-sections on W targets of different thickness, possible contribution of electron capture (EC) to the X-ray production cross-section was estimated to be less than 20%. The degree of multiple ionization of outer shells caused by heavy ion bombardment was estimated from the X-ray line energy shifts and by comparing the X-ray intensity ratios for heavy ions and protons. 相似文献
15.
E. Kemner I. M. de Schepper A. J. M. Schmets H. Grimm 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2000,160(4):544-549
In quasielastic neutron scattering (QENS) the dynamic structure factor S(Q, ω) consists of an elastic central line with area given by the elastic incoherent structure factor (EISF) and a continuous quasielastic broadening. Using only the resolution function of the spectrometer we discuss a method to derive the EISF directly from the raw experimental data points S(Q, ω) without any smoothing or any modelling of the quasielastic broadening. We compare this model to the Fourier transform method, show how it works on actual neutron scattering data and discuss its accuracy for several cases. 相似文献
16.
P. Sellakumar E. James Jebaseelan Samuel 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,264(2):395-399
X-ray computed tomography is one of the potential tool used to evaluate the polymer gel dosimeters in three dimensions. The purpose of this study is to investigate the factors which affect the image noise for X-ray CT polymer gel dosimetry. A cylindrical water filled phantom was imaged with single slice Siemens Somatom Emotion CT scanner. The imaging parameters like tube voltage, tube current, slice scan time, slice thickness and reconstruction algorithm were varied independently to study the dependence of noise on each other. Reductions of noise with number of images to be averaged and spatial uniformity of the image were also investigated. Normoxic polymer gel PAGAT was manufactured and irradiated using Siemens Primus linear accelerator. The radiation induced change in CT number was evaluated using X-ray CT scanner. From this study it is clear that image noise is reduced with increase in tube voltage, tube current, slice scan time, slice thickness and also reduced with increasing the number of images averaged. However to reduce the tube load and total scan time, it was concluded that tube voltage of 130 kV, tube current of 200 mA, scan time of 1.5 s, slice thickness of 3 mm for high dose gradient and 5 mm for low dose gradient were optimal scanning protocols for this scanner. Optimum number of images to be averaged was concluded to be 25 for X-ray CT polymer gel dosimetry. Choice of reconstruction algorithm was also critical. From the study it is also clear that CT number increase with imaging tube voltage and shows the energy dependency of polymer gel dosimeter. Hence for evaluation of polymer gel dosimeters with X-ray CT scanner needs the optimization of scanning protocols to reduce the image noise. 相似文献
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K. Schörner M. GoldammerJ. Stephan 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2011,269(3):292-299
In industrial X-ray cone-beam computed tomography, the inspection of large-scale samples is important because of increasing demands on their quality and long-term mechanical resilience. Large-scale samples, for example made of aluminum or iron, are strongly scattering X-rays. Scattered radiation leads to artifacts such as cupping, streaks, and a reduction in contrast in the reconstructed CT-volume. We propose a scatter correction method based on sampling primary signals by employing a beam-hole array (BHA). In this indirect method, a scatter estimate is calculated by subtraction of the sampled primary signal from the total signal, the latter taken from an image where the BHA is absent. This technique is considered complementary to the better known beam-stop array (BSA) method. The two scatter estimation methods are compared here with respect to geometric effects, scatter-to-total ratio and practicability. Scatter estimation with the BHA method yields more accurate scatter estimates in off-centered regions, and a lower scatter-to-total ratio in critical image regions where the primary signal is very low. Scatter correction with the proposed BHA method is then applied to a ceramic specimen from power generation technologies. In the reconstructed CT volume, cupping almost completely vanishes and contrast is enhanced significantly. 相似文献