The Application of Constrained Signal Reconstruction Methods in High Voltage Impulse Measurement

1988 ◽  
Vol 25 (2) ◽  
pp. 171-181
Author(s):  
D. M. Nagasaka ◽  
M. R. Raghuveer
Keyword(s):  
Least Squares ◽  
High Voltage ◽  
Iterative Reconstruction ◽  
Signal Reconstruction ◽  
Reconstruction Method ◽  
Inadequate Response ◽  
Constrained Least Squares ◽  
Measuring Systems ◽  
Reconstruction Methods ◽  
Impulse Measurement

Two methods of signal reconstruction — the constrained iterative reconstruction method (CIR) and the constrained least squares reconstruction method (CLSR) have been used to compensate for the inadequate response of two high voltage impulse measuring systems. Both methods have been shown to produce accurate estimates. However, the CIR method is favoured as it produces stable results under all of the presented conditions.

Signal Reconstruction in High Voltage Engineering

1988 ◽  
Vol 25 (1) ◽  
pp. 51-57 ◽  
Author(s):  
D. M. Nagasaka ◽  
M. R. Raghuveer
Keyword(s):  
Least Squares ◽  
Frequency Domain ◽  
High Voltage ◽  
Iterative Reconstruction ◽  
Signal Reconstruction ◽  
Constrained Least Squares ◽  
High Voltage Engineering

This paper points out the relevance of signal reconstruction in high voltage engineering and the advantage of considering constrained methods. The application of the constrained least squares and the constrained iterative reconstruction techniques, in the frequency domain, is discussed.

scholarly journals Undersampled Blade Tip-Timing Vibration Reconstruction under Rotating Speed Fluctuation: Uniform and Nonuniform Sensor Configurations

2019 ◽  
Vol 2019 ◽  
pp. 1-13
Author(s):  
Zhongsheng Chen ◽  
Jing He ◽  
Chi Zhan
Keyword(s):  
Signal Reconstruction ◽  
Reconstruction Error ◽  
Reconstruction Method ◽  
Reconstruction Algorithms ◽  
Rotating Speed ◽  
Rotating Blade ◽  
Reconstruction Methods ◽  
Speed Fluctuation ◽  
Blade Tip ◽  
Sensor Configuration

Blade tip-timing (BTT) is a promising method of online monitoring rotating blade vibrations. Since BTT-based vibration signals are typically undersampled, how to reconstruct characteristic vibrations from BTT signals is a big challenge. Existing reconstruction methods are mainly based on the assumption of constant rotation speeds. However, rotating speed fluctuation is inevitable in many engineering applications. In this case, the BTT sampling process should be nonuniform, which will cause existing reconstruction methods to be unavailable. In order to solve this problem, this paper proposes a new reconstruction method based on nonlinear time transformation (NTT). Firstly, the effects of rotating speed fluctuation on BTT vibration reconstruction are analyzed. Next, the NTT of BTT sampling times under rotating speed fluctuation is presented. Then, two NTT-based reconstruction algorithms are derived for uniform and nonuniform BTT sensor configurations, respectively. Also several evaluation metrics of BTT vibration reconstruction under rotating speed fluctuation are defined. Finally, numerical simulations are done to verify the proposed algorithms. The results testify that the proposed NTT-based reconstruction method can reduce effectively the influence of rotating speed fluctuation and decrease the reconstruction error. In addition, rotating speed fluctuation has more bad effects on the reconstruction method under nonuniform sensor configuration than under uniform sensor configuration. For nonuniform BTT signal reconstruction under rotating speed fluctuation, more attentions should be paid on selecting proper angles between BTT sensors. In summary, the proposed method will benefit for detecting early blade damages by reducing frequency aliasing.

Improvements to image quality using hybrid and model-based iterative reconstructions: a phantom study

2016 ◽  
Vol 58 (1) ◽  
pp. 53-61 ◽  
Author(s):  
Marie-Louise Aurumskjöld ◽  
Kristina Ydström ◽  
Anders Tingberg ◽  
Marcus Söderberg
Keyword(s):  
Image Quality ◽  
Radiation Dose ◽  
Iterative Reconstruction ◽  
Power Spectra ◽  
Reconstruction Method ◽  
Noise Power ◽  
Contrast Resolution ◽  
Low Contrast ◽  
Model Based ◽  
Reconstruction Methods

Background The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose. Purpose To investigate how image quality depends on reconstruction method and to discuss patient dose reduction resulting from the use of hybrid and model-based iterative reconstruction. Material and Methods An image quality phantom (Catphan® 600) and an anthropomorphic torso phantom were examined on a Philips Brilliance iCT. The image quality was evaluated in terms of CT numbers, noise, noise power spectra (NPS), contrast-to-noise ratio (CNR), low-contrast resolution, and spatial resolution for different scan parameters and dose levels. The images were reconstructed using filtered back projection (FBP) and different settings of hybrid (iDose4) and model-based (IMR) iterative reconstruction methods. Results iDose4 decreased the noise by 15–45% compared with FBP depending on the level of iDose4. The IMR reduced the noise even further, by 60–75% compared to FBP. The results are independent of dose. The NPS showed changes in the noise distribution for different reconstruction methods. The low-contrast resolution and CNR were improved with iDose4, and the improvement was even greater with IMR. Conclusion There is great potential to reduce noise and thereby improve image quality by using hybrid or, in particular, model-based iterative reconstruction methods, or to lower radiation dose and maintain image quality.

scholarly journals A Novel Reconstruction Method for Measurement Data Based on MTLS Algorithm

Sensors ◽  
2020 ◽  
Vol 20 (22) ◽  
pp. 6449
Author(s):  
Tianqi Gu ◽  
Chenjie Hu ◽  
Dawei Tang ◽  
Tianzhi Luo
Keyword(s):  
Least Squares ◽  
Measurement Data ◽  
Local Approximation ◽  
Reconstruction Method ◽  
Random Errors ◽  
Least Trimmed Squares ◽  
Approximation Accuracy ◽  
Robust Model ◽  
Reconstruction Methods ◽  
Measurement Experiment

Reconstruction methods for discrete data, such as the Moving Least Squares (MLS) and Moving Total Least Squares (MTLS), have made a great many achievements with the progress of modern industrial technology. Although the MLS and MTLS have good approximation accuracy, neither of these two approaches are robust model reconstruction methods and the outliers in the data cannot be processed effectively as the construction principle results in distorted local approximation. This paper proposes an improved method that is called the Moving Total Least Trimmed Squares (MTLTS) to achieve more accurate and robust estimations. By applying the Total Least Trimmed Squares (TLTS) method to the orthogonal construction way in the proposed MTLTS, the outliers as well as the random errors of all variables that exist in the measurement data can be effectively suppressed. The results of the numerical simulation and measurement experiment show that the proposed algorithm is superior to the MTLS and MLS method from the perspective of robustness and accuracy.

Image Reconstruction with the Fourier Coefficients for Magnetic Induction Tomography

2020 ◽  
Vol 16 (2) ◽  
pp. 156-163
Author(s):  
Jingwen Wang ◽  
Xu Wang ◽  
Dan Yang ◽  
Kaiyang Wang
Keyword(s):  
Inverse Problem ◽  
Image Reconstruction ◽  
Magnetic Induction ◽  
Fourier Coefficients ◽  
Signal Reconstruction ◽  
Reconstruction Algorithm ◽  
Reconstruction Method ◽  
Measurement Equation ◽  
Image Reconstruction Method ◽  
Magnetic Induction Tomography

Background: Image reconstruction of magnetic induction tomography (MIT) is a typical ill-posed inverse problem, which means that the measurements are always far from enough. Thus, MIT image reconstruction results using conventional algorithms such as linear back projection and Landweber often suffer from limitations such as low resolution and blurred edges. Methods: In this paper, based on the recent finite rate of innovation (FRI) framework, a novel image reconstruction method with MIT system is presented. Results: This is achieved through modeling and sampling the MIT signals in FRI framework, resulting in a few new measurements, namely, fourier coefficients. Because each new measurement contains all the pixel position and conductivity information of the dense phase medium, the illposed inverse problem can be improved, by rebuilding the MIT measurement equation with the measurement voltage and the new measurements. Finally, a sparsity-based signal reconstruction algorithm is presented to reconstruct the original MIT image signal, by solving this new measurement equation. Conclusion: Experiments show that the proposed method has better indicators such as image error and correlation coefficient. Therefore, it is a kind of MIT image reconstruction method with high accuracy.

scholarly journals Fractional Differential Equation-Based Instantaneous Frequency Estimation for Signal Reconstruction

2021 ◽  
Vol 5 (3) ◽  
pp. 83
Author(s):  
Bilgi Görkem Yazgaç ◽  
Mürvet Kırcı
Keyword(s):  
Differential Equation ◽  
Fractional Differential Equation ◽  
Frequency Estimation ◽  
Signal Reconstruction ◽  
Reconstruction Method ◽  
Reconstruction Algorithms ◽  
Instantaneous Frequency Estimation ◽  
Proposed Model ◽  
Fractional Differential ◽  
Instantaneous Frequencies

In this paper, we propose a fractional differential equation (FDE)-based approach for the estimation of instantaneous frequencies for windowed signals as a part of signal reconstruction. This approach is based on modeling bandpass filter results around the peaks of a windowed signal as fractional differential equations and linking differ-integrator parameters, thereby determining the long-range dependence on estimated instantaneous frequencies. We investigated the performance of the proposed approach with two evaluation measures and compared it to a benchmark noniterative signal reconstruction method (SPSI). The comparison was provided with different overlap parameters to investigate the performance of the proposed model concerning resolution. An additional comparison was provided by applying the proposed method and benchmark method outputs to iterative signal reconstruction algorithms. The proposed FDE method received better evaluation results in high resolution for the noniterative case and comparable results with SPSI with an increasing iteration number of iterative methods, regardless of the overlap parameter.

Global Inhomogeneity Index Evaluation of a DCT-based EIT Lung Imaging

2020 ◽  
Vol 6 (3) ◽  
pp. 36-39
Author(s):  
Rongqing Chen ◽  
Knut Möller
Keyword(s):  
Classical Method ◽  
Lung Imaging ◽  
Imaging Method ◽  
Reconstruction Method ◽  
Essential Information ◽  
Preliminary Results ◽  
Reconstruction Methods ◽  
Comparison Results ◽  
Index Evaluation ◽  
Inhomogeneity Index

AbstractPurpose: To evaluate a novel structural-functional DCT-based EIT lung imaging method against the classical EIT reconstruction. Method: Taken retrospectively from a former study, EIT data was evaluated using both reconstruction methods. For different phases of ventilation, EIT images are analyzed with respect to the global inhomogeneity (GI) index for comparison. Results: A significant less variant GI index was observed in the DCTbased method, compared to the index from classical method. Conclusion: The DCT-based method generates more accurate lung contour yet decreasing the essential information in the image which affects the GI index. These preliminary results must be consolidated with more patient data in different breathing states.

scholarly journals Efficacy and safety of fremanezumab in patients with migraine and inadequate response to prior preventive treatment: subgroup analyses by country of a randomized, placebo-controlled trial

2021 ◽  
Vol 22 (1) ◽  
Author(s):  
Egilius L. H. Spierings ◽  
Mikko Kärppä ◽  
Xiaoping Ning ◽  
Joshua M. Cohen ◽  
Verena Ramirez Campos ◽  
...  
Keyword(s):  
United States ◽  
Czech Republic ◽  
Adverse Events ◽  
Least Squares ◽  
The United States ◽  
Inadequate Response ◽  
Double Blind ◽  
Monthly Average ◽  
Preventive Medication ◽  
Subgroup Analyses

Abstract Background The FOCUS study evaluated the efficacy of migraine preventive medications across different countries within the same patient population, particularly for patients with difficult-to-treat migraine. These prespecified subgroup analyses evaluated efficacy by country in the FOCUS study of fremanezumab in adults with episodic migraine or chronic migraine and documented inadequate response to 2 to 4 migraine preventive medication classes. Methods Overall, 838 participants were enrolled in the FOCUS study, a randomized, double-blind, placebo-controlled, parallel-group, phase 3b study performed at 104 sites. For 12 weeks of double-blind treatment, patients were randomized (1:1:1) to quarterly fremanezumab, monthly fremanezumab, or matched placebo. The primary efficacy endpoint was the mean change from baseline in monthly average migraine days over 12 weeks of double-blind treatment, evaluated by country in these subgroup analyses. Results Of 14 countries contributing data, the Czech Republic (n = 188/838; 22%), the United States (n = 120/838; 14%), and Finland (n = 85/838; 10%) enrolled the most patients. Changes from baseline in monthly average migraine days over 12 weeks were significantly greater with fremanezumab versus placebo for patients in these countries: Czech Republic (least-squares mean difference versus placebo [95% confidence interval]: quarterly fremanezumab, − 1.9 [− 3.25, − 0.47]; P = 0.009; monthly fremanezumab, − 3.0 [− 4.39, − 1.59]; P < 0.001), the United States (quarterly fremanezumab, − 3.7 [− 5.77, − 1.58]; P < 0.001; monthly fremanezumab, − 4.2 [− 6.23, − 2.13]; P < 0.001), and Finland (quarterly fremanezumab, − 3.0 [− 5.32, − 0.63]; P = 0.014; monthly fremanezumab, − 3.9 [− 6.27, − 1.44]; P = 0.002). Results were comparable for the remaining 9 countries, with the least-squares mean difference versus placebo ranging from – 5.6 to – 2.4 with quarterly fremanezumab and from − 5.3 to − 1.5 with monthly fremanezumab. Incidences of serious adverse events and adverse events leading to discontinuation were low and comparable across countries and treatment groups. Conclusions Monthly and quarterly fremanezumab significantly reduced the monthly average number of migraine days versus placebo regardless of country and continent (North America versus Europe) in migraine patients with documented inadequate response to 2 to 4 migraine preventive medication classes. Trial registration ClinicalTrials.gov Identifier: NCT03308968.

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