Browsing by Author "Chen, Chi-Jen"

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Automated Segmentation and Quantification of White Matter Hyperintensities in Acute Ischemic Stroke Patients with Cerebral Infarction
(2014-08-15)
Tsai, Jang-Zern
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Peng, Syu-Jyun
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Chen, Yu-Wei
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Wang, Kuo-Wei
;
Li, Chen-Hua
White matter hyperintensities (WMHs) of presumed vascular origin are common in ageing population, especially in patients with acute cerebral infarction and the volume has been reported to be associated with mental impairment and the risk of hemorrhage from antithrombotic agents. WMHs delineation can be computerized to minimize human bias. However, the presence of cerebral infarcts greatly degrades the accuracy of WMHs detection and thus limits the application of computerized delineation to patients with acute cerebral infarction. We propose a computer-assisted segmentation method to depict WMHs in the presence of cerebral infarcts in combined T1-weighted, fluid attenuation inversion recovery, and diffusion-weighted magnetic resonance imaging (MRI). The proposed method detects WMHs by empirical threshold and atlas information, with subtraction of white matter voxels affected by acute infarction. The method was derived using MRI from 25 hemispheres with WMHs only and 13 hemispheres with both WMHs and cerebral infarcts. Similarity index (SI) and correlation were utilized to assess the agreement between the new automated method and a gold standard visually guided semi-automated method done by an expert rater. The proposed WMHs segmentation approach produced average SI, sensitivity and specificity of 83.142 +/- 11.742, 84.154 +/- 16.086 and 99.988 +/- 0.029% with WMHs only and of 68.826 +/- 14.036, 74.381 +/- 18.473 and 99.956 +/- 0.054% with both WMHs and cerebral infarcts in the derivation cohort. The performance of the proposed method with an external validation cohort was also highly consistent with that of the experienced rater.
Automatic Detection and Quantification of Acute Cerebral Infarct by Fuzzy Clustering and Histographic Characterization on Diffusion Weighted MR Imaging and Apparent Diffusion Coefficient Map
(2014)
Tsai, Jang-Zern
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Peng, Syu-Jyun
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Chen, Yu-Wei
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Wang, Kuo-Wei
;
Wu, Hsiao-Kuang
Determination of the volumes of acute cerebral infarct in the magnetic resonance imaging harbors prognostic values. However, semiautomatic method of segmentation is time-consuming and with high interrater variability. Using diffusion weighted imaging and apparent diffusion coefficient map from patients with acute infarction in 10 days, we aimed to develop a fully automatic algorithm to measure infarct volume. It includes an unsupervised classification with fuzzy C-means clustering determination of the histographic distribution, defining self-adjusted intensity thresholds. The proposed method attained high agreement with the semiautomatic method, with similarity index 89.9 +/- 6.5%, in detecting cerebral infarct lesions from 22 acute stroke patients. We demonstrated the accuracy of the proposed computer-assisted prompt segmentation method, which appeared promising to replace the laborious, time-consuming, and operator-dependent semiautomatic segmentation.
Development and Application of a Vibration Isolation System with Adaptive Stiffness Considering Potential Energy
(2015-01-01)
Chen, Chi-Jen
;
Lin, Tzu-Kang
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土木工程學系
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Department of Civil Engineering
In recent years, a study of a semi-active isolation system named the Leverage-type Stiffness Controllable Isolation System (LSCIS) was proposed. The main concept of the LSCIS is to adjust the stiffness in the isolator for the fundamental period of the superstructure by a simple leverage mechanism. Although great performance has been achieved with the support of the least input energy method (LIEM) in far-field earthquakes, some results still reveal that the proposed system is not suitable for application in near-fault strong ground motion. To overcome this problem, two algorithms that consider the potential energy effect in the semi-active structural control system are proposed in this study. The optimal weightings between the potential and kinetic energy are first determined through a series of near-fault earthquake simulations. The proposed algorithms are then developed with the combination of the potential energy (Ep) and the kinetic energy (Ep) as the control objective to reduce the structural displacement responses efficiently. In order to demonstrate the performance of the proposed algorithm, a two-degree-of-freedom structure is used as a benchmark in both numerical simulation and experimental verification. Numerical results have shown that the dynamic response of the structure can be effectively alleviated by the proposed algorithm under both far-field and near-fault earthquakes, while the structural responses by the LIEM may be worse than the pure passive control. The feasibility of implementing the proposed system has also been experimentally verified.
Semi-active leverage-type isolation system considering minimum structural energy
(2018-03-01)
Lin, Tzu-Kang
;
Lu, Lyan-Ywan
;
Chen, Chi-Jen
;
土木工程學系
;
Department of Civil Engineering
Semi-active isolation systems based on leverage-type stiffness control strategies have been widely studied. The main concept behind this type of system is to adjust the stiffness in the isolator to match the fundamental period of the isolated system by using a simple leverage mechanism. Although this system achieves high performance under far-field earthquakes, it is unsuitable for near-fault strong ground motion. To overcome this problem, this study considers the potential energy effect in the control law of the semi-active isolation system. The minimal energy weighting (MEW) between the potential energy and kinetic energy was first optimized through a series of numerical simulations. Two MEW algorithms, namely generic and near-fault MEW control, were then developed to efficiently reduce the structural displacement responses. To demonstrate the performance of the proposed method, a two-degree-of-freedom structure was employed as a benchmark. Numerical results indicate that the dynamic response of the structure can be effectively dampened by the proposed MEW control under both far-field and near-fault earthquakes, whereas the structural responses resulting from conventional control methods may be greater than those for the purely passive control method. Moreover, according to experimental verifications, both the generic and near-fault MEW control modes yielded promising results under impulse-like earthquakes. The practicability of the proposed control algorithm was verified.