The aim of this work is to study the imagereconstruction of capacitively coupled electrical impedance tomography (CCEIT) by using total impedance of a gas-liquid two-phase flow. The results of imagereconstruction th...
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The aim of this work is to study the imagereconstruction of capacitively coupled electrical impedance tomography (CCEIT) by using total impedance of a gas-liquid two-phase flow. The results of imagereconstruction that utilise the real part, the imaginary part, the amplitude of the impedance, and the imagereconstruction results by making use of different parts of the total impedance are investigated and discussed. By combining a linear back projection (LBP) algorithm and a K-means clustering algorithm, a new image reconstruction algorithm for CCEIT is proposed. The LBP is used to obtain the original reconstructed image. The K-means is adopted to automatically obtain the gray level threshold. The final reconstructed image is acquired with an established gray level threshold filter. With the new algorithm (LBP + K-means), the images reconstructed by using different parts of the impedance are obtained. To make full use of total impedance information, an image fusion method based on the weighted combination method is presented. With a developed 12-electrode CCEIT prototype, the imagereconstruction experiments are conducted. Experimental results show that all three parts of the impedance can reflect the phase distribution characteristics of the gas-liquid two-phase flow from different aspects. image fusion results indicate that making full use of the different parts of the total impedance of the gas-liquid two-phase flow can effectively improve the quality of the imagereconstruction. The experimental results also verify the feasibility and the effectiveness of the proposed new image reconstruction algorithm. Compared with conventional algorithms, the proposed imagereconstruction method can obtain comparable/better imagereconstruction results with less prior knowledge. The influence of manual intervention on the imagereconstruction results can be effectively avoided.
Currently, most of the electrical tomography measurement systems are developed on microcontroller units, digital signal processors, or field programmable gate arrays, whereas imagereconstruction and display functions...
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Currently, most of the electrical tomography measurement systems are developed on microcontroller units, digital signal processors, or field programmable gate arrays, whereas imagereconstruction and display functions are implemented in a separate host computer. Therefore, the complete hardware usually comprises a measurement system and an imagereconstruction computer. The current trend is to develop industrial standard electrical tomography systems, which can implement the imagereconstruction and measurement functions into an integrated processor/chip. However, most of the above mentioned processors do not provide the necessary computational resources as required by the computationally intensive imagereconstruction function. This paper describes a hardware scheme for implementing imagereconstruction functions on a heterogeneous hardware platform, wherein the processor system and programmable logics (PLs) are tightly coupled and can achieve better resource utilization and overall system performance. By adopting a high-level synthesis method, the image reconstruction algorithms can be realized jointly by the PLs and processor system. In this hardware scheme, the algorithms are properly optimized to achieve better data throughput and execution efficiency, that is, by utilizing parallel computation in PLs. Details of the hardware scheme and method of accelerating the imagereconstruction process are presented in this paper. Implementation results show that the proposed heterogeneous hardware scheme can achieve the imagereconstruction rates of 24 and 1700 frames per second while employing the iterative and non-iterative algorithms, respectively.
Photoacoustic imaging (PAI) has the potential to acquire 3-D optical images at high speed. Attempts at 3-D photoacoustic imaging have used a dense 2-D array of ultrasound detectors or have densely scanned a single det...
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Photoacoustic imaging (PAI) has the potential to acquire 3-D optical images at high speed. Attempts at 3-D photoacoustic imaging have used a dense 2-D array of ultrasound detectors or have densely scanned a single detector on a 2-D surface. The former approach is costly and complicated to realize, while the latter is inherently slow. We present a different approach based on a sparse 2-D array of detector elements and an iterative reconstructionalgorithm. This approach has the potential for fast image acquisition, since no mechanical scanning is required, and for simple and compact construction due to the smaller number of detector elements. We obtained spatial sensitivity maps of the sparse array and used them to optimize the image reconstruction algorithm. We then validated the method on phantoms containing 3-D distributions of optically absorbing point sources. reconstruction of the point sources from the time-domain signals resulted in images with good contrast and accurate localization (<= 1 mm error). image acquisition time was 1 s. The results suggest that 3-D PAI with a sparse array of detector elements is a viable approach. Furthermore, the rapid acquisition speed indicates the possibility of high frame rate 3-D PAI. (C) 2008 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.2992131]
Considering the influence of the limited measurement data on the effectiveness of the image reconstruction algorithms in industrial multiphase flow tomography, an iterative filtering reconstructionalgorithm is propos...
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Considering the influence of the limited measurement data on the effectiveness of the image reconstruction algorithms in industrial multiphase flow tomography, an iterative filtering reconstructionalgorithm is proposed by redefining inverse problem in this article. In order to improve the image quality in iterative reconstructionalgorithm, Wiener filter and soft-threshold algorithm are employed as constraints for the reconstructed image. The developed algorithm is applied to gamma-CT based two-phase flow measurements, both simulated and experimental. The results demonstrate that the proposed method cannot only realize the flow regime identification on horizontal pipe, but also improve the iterative reconstruction process, i.e., the reconstructed image quality is enhanced and the iteration number is reduced.
For online monitoring of complex temperature distributions, an acoustic tomography system based on sound travel-time measurement is developed. For coping with the reverberation phenomenon in actual measurement, an ant...
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For online monitoring of complex temperature distributions, an acoustic tomography system based on sound travel-time measurement is developed. For coping with the reverberation phenomenon in actual measurement, an anti-reflection interference measurement method for sound travel-time is proposed based on cross-correlation and peak recognition. In view of the fact the pixel number provided by commonly used reconstructionalgorithms, such as least-squares methods, is very limited, radial basis function approximation and regularisation technique are used, which leads to the pixel number of the reconstructionimage increasing dramatically. Mixed programming with LabVIEW and MATLAB is used. Queue structure is adopted to make data acquiring program and data processing program parallel. Test results show that the system can run normally as designed. The measurement values of sound travel-time acquired by the proposed method are stable even in strong reflection interference. Test results show that the system can run normally as designed. The measurement values of sound travel-time acquired by the proposed method are stable even in strong reflection interference. The temperature fields reconstructed are coincided with actual fields, and correctly reflect the temperature changes in the measured area with the heater number, heater location and heating time.
The real-time capability becomes more and more important for the millimeter-wave imaging systems in variety of applications. To achieve this purpose, the imaging scheme with multiple-input-multiple-output (MIMO) is on...
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The real-time capability becomes more and more important for the millimeter-wave imaging systems in variety of applications. To achieve this purpose, the imaging scheme with multiple-input-multiple-output (MIMO) is one of the potential ways, while still limited by the high computational complexity of the conventional MIMO image reconstruction algorithm, which is commonly based on the back-projection theorem. In this letter, an efficient phase shift migration (PSM) image reconstruction algorithm was proposed to improve the computation efficiency for MIMO systems 2-D imaging. By decomposing and approximating the PSM operator reasonably, only complex multiplication and Fourier transform (FT) operations are employed which can be easily carried out to reduce computation cost. An MIMO side-looking prototype system was designed for proof experiments in the 100-GHz band. Although the proposed algorithm introduces a negligible phase error, the experimental results show that the error can be ignored and the algorithm can achieve high-precision real-time imaging.
A millimeter-wave (MMW) inline holographic imaging method based on step-frequency continuous-wave (SFCW) scheme is presented in this letter. By analyzing and decomposing the received SFCW power in range domain, it is ...
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A millimeter-wave (MMW) inline holographic imaging method based on step-frequency continuous-wave (SFCW) scheme is presented in this letter. By analyzing and decomposing the received SFCW power in range domain, it is found that the background and twin-image interferences can be well separated from the image-related term, and therefore can be removed with appropriate range windows. Moreover, a corresponding mathematical algorithm is developed to reconstruct the image from the inline hologram. To validate the effectiveness of the presented approach, a 200-GHz prototype system is designed and fabricated. Experimental results demonstrate the good performance of the imaging system and its potential application in high-resolution target detection.
This study presents a method to increase the signal-to-noise ratio (SNR) and image stability in magnetic inductance tomography (MIT) data acquisition by exploiting transient response analysis. In front-end circuits fo...
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This study presents a method to increase the signal-to-noise ratio (SNR) and image stability in magnetic inductance tomography (MIT) data acquisition by exploiting transient response analysis. In front-end circuits for inductance measurements in MIT, a critical step is the phase sensitive demodulation, which includes a low pass filter. When the excitation source is switched from one coil to the next, a transient response occurs as the received voltage level changes. Normally, data acquisition takes place after the transient response finishes and the voltage level becomes nearly constant. In this study, a method is proposed to increase the SNR by exploiting the information embedded in the transient response. Simulation and experimental tests have confirmed the validity of the method;standard deviations of the measured inductance decrease more than 50%. The impact of improvement in SNR in raw inductance measurement on image stability is considered with different image reconstruction algorithms. The error propagation in the imagereconstruction process is discussed.
On the basis that a gas/liquid two-phase flow was considered as a strongly inhomogeneous medium due to the high contrast in acoustic impedance distribution, the authors analysed the inherent dependency of the incomple...
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On the basis that a gas/liquid two-phase flow was considered as a strongly inhomogeneous medium due to the high contrast in acoustic impedance distribution, the authors analysed the inherent dependency of the incomplete tomographic projections on the distribution of bubbles in liquid when using transmission-mode (TM) ultrasound computerized tomography (UCT). A mathematical model describing the acoustic characteristics of this flow was established. A transmission-mode ultrasonic system for tomographic imaging of gas/liquid flow was designed based upon a fast binary back-projection image reconstruction algorithm. Emphasis was made on the evaluation of its performance and its application to flow regime identification. Several flow pattern models were made and the corresponding monitoring results were given. Finally, limitations and possible future implementations of the system are discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.
Endoscopic diffuse optical tomography (DOT) is a new medical imaging modality with the potential applications in functional imaging of the internal organs. To cut down the measurement time and the computation burden o...
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Endoscopic diffuse optical tomography (DOT) is a new medical imaging modality with the potential applications in functional imaging of the internal organs. To cut down the measurement time and the computation burden of imagereconstruction, in this paper, we developed the image reconstruction algorithm with the partial measurement in the effective detection range (EDR) of a tubular tissue and the corresponding endoscopic imaging system with a novel endoscopic probe for flexibly selecting the detection sites. For a typical inner size and optical properties of the cervix, it is found that EDR is less than half of the inner circumference. Comparing to the traditional method, the adoption of EDR results in a reduction of more than a factor of two in the time cost for a measurement cycle and for the total iteration reconstruction. images reconstructed from the simulation data demonstrate that the proposed method achieves equivalent image quality to that obtained from the complete data set. The images reconstructed from the EDR measurements on cervix-like solid phantoms show that both the location and size of the targets are reconstructed correctly. The proposed method will be useful to the development of endoscopic DOT technologies for cancer detection in tubular organs including cervix.
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