In the adjoint-state method, the forward-propagated source wavefield and the backward-propagated receiver wavefield must be available simultaneously either for seismic imaging in migration or for gradient calculation ...In the adjoint-state method, the forward-propagated source wavefield and the backward-propagated receiver wavefield must be available simultaneously either for seismic imaging in migration or for gradient calculation in inversion. A feasible way to avoid the excessive storage demand is to reconstruct the source wavefield backward in time by storing the entire history of the wavefield in perfectly matched layers. In this paper, we make full use of the elementwise global property of the Laplace operator of the spectral element method (SEM) and propose an efficient source wavefield reconstruction method at the cost of storing the wavefield history only at single boundary layer nodes. Numerical experiments indicate that the accuracy of the proposed method is identical to that of the conventional method and is independent of the order of the Lagrange polynomials, the element type, and the temporal discretization method. In contrast, the memory-saving ratios of the conventional method versus our method is at least N when using either quadrilateral or hexahedron elements, respectively, where N is the order of the Lagrange polynomials used in the SEM. A higher memorysaving ratio is achieved with triangular elements versus quadrilaterals. The new method is applied to reverse time migration by considering the Marmousi model as a benchmark. Numerical results demonstrate that the method is able to provide the same result as the conventional method but with about 1/25 times lower storage demand. With the proposed wavefield reconstruction method, the storage demand is dramatically reduced;therefore, in-core memory storage is feasible even for large-scale three-dimensional adjoint inversion problems.展开更多
A two-stage source reconstruction algorithm for bioluminescence tomography (BLT) is developed using hybrid finite element method (FEM). The proposed algorithm takes full advantages of linear and quadratic FEMs, which ...A two-stage source reconstruction algorithm for bioluminescence tomography (BLT) is developed using hybrid finite element method (FEM). The proposed algorithm takes full advantages of linear and quadratic FEMs, which can be used to localize and quantify bioluminescent source accurately. In the first stage, a large permissible region is roughly determined and then iteratively evolved to reduce matrix dimension using efficient linear FEM. In the final stage, high-convergence quadratic FEM is applied to improve reconstruction result. Both numerical simulation and physical experiment are performed to evaluate the proposed algorithm. The relevant results demonstrate that quantitative reconstruction can be well achieved in terms of computation efficiency, source position, power density, and total power when compared with previous studies.展开更多
The accuracy of the background optical properties has a considerable effect on the quality of reconstructed images in near-infrared functional brain imaging based on continuous wave diffuse optical tomography（CW-DOT...The accuracy of the background optical properties has a considerable effect on the quality of reconstructed images in near-infrared functional brain imaging based on continuous wave diffuse optical tomography（CW-DOT）. We propose a region stepwise reconstruction method in CW-DOT scheme for reconstructing the background absorption and reduced scattering coefficients of the two-layered slab sample with the known geometric information. According to the relation between the thickness of the top layer and source– detector separation, the conventional measurement data are divided into two groups and are employed to reconstruct the top and bottom background optical properties, respectively. The numerical simulation results demonstrate that the proposed method can reconstruct the background optical properties of two-layered slab sample effectively. The region-of-interest reconstruction results are better than those of the conventional simultaneous reconstruction method.展开更多
目的探讨二代双源CT低管电压（100 k V）结合基于原始数据的迭代重建（SAFIRE）在冠状动脉支架成像中的临床应用价值。方法搜集冠状动脉支架术后行双源冠状动脉CTA检查者66例,对于支架植入段分别行常规滤波反投影法重建（FBP）及迭代重...目的探讨二代双源CT低管电压（100 k V）结合基于原始数据的迭代重建（SAFIRE）在冠状动脉支架成像中的临床应用价值。方法搜集冠状动脉支架术后行双源冠状动脉CTA检查者66例,对于支架植入段分别行常规滤波反投影法重建（FBP）及迭代重建（SAFIRE）,冠状动脉CTA检查后2周内均行冠状动脉DSA检查,将FBP结果与SAFIRE结果分别与DSA检查结果对照。结果 DSA复查证实：轻度内膜增生者16例,再狭窄8例,光滑42例。FBP重建示再狭窄17例,内膜增生9例,光滑40例;SAFIRE示内膜增生者16例,再狭窄者9例,光滑者41例。FBP诊断支架再狭窄准确性77.3%,敏感性62.5%,特异性79.3%,阳性预测值29.4%,阴性预测值93.9%;SAFIRE诊断支架再狭窄准确性98.5%,敏感性100%,特异性98.3%,阳性预测值88.9%,阴性预测值100%。ROC曲线示SAFIRE方式线下面积为0.991;FBP方式线下面积为0.709。结论二代双源CT低管电压结合SAFIRE重建冠状动脉CTA可有效消除支架所带来的伪影,判断支架有无内膜增生、有无再狭窄明显优于FBP重建,SAFIRE较FBP预测支架再狭窄与DSA具有更好的一致性。提示双源CT低管电压结合SAFIRE重建冠状动脉CTA检查可作为临床支架术后复查的有效手段。展开更多
基金financial support for this work contributed by the National Key Research and Development Program of China (grant numbers 2016YFC0600101 and 2016YFC 0600201)the National Natural Science Foundation of China (grant numbers 41874065, 41604076, 41674102, 41674095, 41522401, 41574082, and 41774097)
文摘In the adjoint-state method, the forward-propagated source wavefield and the backward-propagated receiver wavefield must be available simultaneously either for seismic imaging in migration or for gradient calculation in inversion. A feasible way to avoid the excessive storage demand is to reconstruct the source wavefield backward in time by storing the entire history of the wavefield in perfectly matched layers. In this paper, we make full use of the elementwise global property of the Laplace operator of the spectral element method (SEM) and propose an efficient source wavefield reconstruction method at the cost of storing the wavefield history only at single boundary layer nodes. Numerical experiments indicate that the accuracy of the proposed method is identical to that of the conventional method and is independent of the order of the Lagrange polynomials, the element type, and the temporal discretization method. In contrast, the memory-saving ratios of the conventional method versus our method is at least N when using either quadrilateral or hexahedron elements, respectively, where N is the order of the Lagrange polynomials used in the SEM. A higher memorysaving ratio is achieved with triangular elements versus quadrilaterals. The new method is applied to reverse time migration by considering the Marmousi model as a benchmark. Numerical results demonstrate that the method is able to provide the same result as the conventional method but with about 1/25 times lower storage demand. With the proposed wavefield reconstruction method, the storage demand is dramatically reduced;therefore, in-core memory storage is feasible even for large-scale three-dimensional adjoint inversion problems.
基金supported by National Basic Research Program of China (973 Program) (No. 2011CB707702)National Natural Science Foundation of China (Nos. 81090272, 81000632, and 30900334)+1 种基金the Shaanxi Provincial Natural Science Foundation (No. 2009JQ8018)the Fundamental Research Funds for the Central Universities
文摘A two-stage source reconstruction algorithm for bioluminescence tomography (BLT) is developed using hybrid finite element method (FEM). The proposed algorithm takes full advantages of linear and quadratic FEMs, which can be used to localize and quantify bioluminescent source accurately. In the first stage, a large permissible region is roughly determined and then iteratively evolved to reduce matrix dimension using efficient linear FEM. In the final stage, high-convergence quadratic FEM is applied to improve reconstruction result. Both numerical simulation and physical experiment are performed to evaluate the proposed algorithm. The relevant results demonstrate that quantitative reconstruction can be well achieved in terms of computation efficiency, source position, power density, and total power when compared with previous studies.
基金supported by the National Natural Science Foundation of China(Nos.81271618 and 81371602)the Tianjin Municipal Government of China(Nos.12JCQNJC09400 and 13JCZDJC28000)the Research Fund for the Doctoral Program of Higher Education of China(No.20120032110056)
文摘The accuracy of the background optical properties has a considerable effect on the quality of reconstructed images in near-infrared functional brain imaging based on continuous wave diffuse optical tomography（CW-DOT）. We propose a region stepwise reconstruction method in CW-DOT scheme for reconstructing the background absorption and reduced scattering coefficients of the two-layered slab sample with the known geometric information. According to the relation between the thickness of the top layer and source– detector separation, the conventional measurement data are divided into two groups and are employed to reconstruct the top and bottom background optical properties, respectively. The numerical simulation results demonstrate that the proposed method can reconstruct the background optical properties of two-layered slab sample effectively. The region-of-interest reconstruction results are better than those of the conventional simultaneous reconstruction method.
文摘目的探讨二代双源CT低管电压（100 k V）结合基于原始数据的迭代重建（SAFIRE）在冠状动脉支架成像中的临床应用价值。方法搜集冠状动脉支架术后行双源冠状动脉CTA检查者66例,对于支架植入段分别行常规滤波反投影法重建（FBP）及迭代重建（SAFIRE）,冠状动脉CTA检查后2周内均行冠状动脉DSA检查,将FBP结果与SAFIRE结果分别与DSA检查结果对照。结果 DSA复查证实：轻度内膜增生者16例,再狭窄8例,光滑42例。FBP重建示再狭窄17例,内膜增生9例,光滑40例;SAFIRE示内膜增生者16例,再狭窄者9例,光滑者41例。FBP诊断支架再狭窄准确性77.3%,敏感性62.5%,特异性79.3%,阳性预测值29.4%,阴性预测值93.9%;SAFIRE诊断支架再狭窄准确性98.5%,敏感性100%,特异性98.3%,阳性预测值88.9%,阴性预测值100%。ROC曲线示SAFIRE方式线下面积为0.991;FBP方式线下面积为0.709。结论二代双源CT低管电压结合SAFIRE重建冠状动脉CTA可有效消除支架所带来的伪影,判断支架有无内膜增生、有无再狭窄明显优于FBP重建,SAFIRE较FBP预测支架再狭窄与DSA具有更好的一致性。提示双源CT低管电压结合SAFIRE重建冠状动脉CTA检查可作为临床支架术后复查的有效手段。
