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Harrach, Bastian,Jin Keun Seo,Eung Je Woo IEEE 2010 IEEE transactions on medical imaging Vol.29 No.11
<P>Time-difference electrical impedance tomography (tdEIT) requires two data sets measured at two different times. The difference between them is utilized to produce images of time-dependent changes in a complex conductivity distribution inside the human body. Frequency-difference EIT (fdEIT) was proposed to image frequency-dependent changes of a complex conductivity distribution. It has potential applications in tumor and stroke imaging since it can visualize an anomaly without requiring any time-reference data obtained in the absence of an anomaly. In this paper, we provide a rigorous analysis for the detectability of an anomaly based on a constructive and quantitative physical correlation between a measured fdEIT data set and an anomaly. From this, we propose a new noniterative frequency-difference anomaly detection method called the factorization method (FM) and elaborate its physical justification. To demonstrate its practical applicability, we performed fdEIT phantom imaging experiments using a multifrequency EIT system. Applying the FM to measured frequency-difference boundary voltage data sets, we could quantitatively evaluate indicator functions inside the imaging domain, of which values at each position reveal presence or absence of an anomaly. We found that the FM successfully localizes anomalies inside an imaging domain with a frequency-dependent complex conductivity distribution. We propose the new FM as an anomaly detection algorithm in fdEIT for potential applications in tumor and stroke imaging.</P>
Monotonicity-based electrical impedance tomography for lung imaging
Zhou, Liangdong,Harrach, Bastian,Seo, Jin Keun IOP 2018 Inverse problems Vol.34 No.4
<P>This paper presents a monotonicity-based spatiotemporal conductivity imaging method for continuous regional lung monitoring using electrical impedance tomography (EIT). The EIT data (i.e. the boundary current–voltage data) can be decomposed into pulmonary, cardiac and other parts using their different periodic natures. The time-differential current–voltage operator corresponding to the lung ventilation can be viewed as either semi-positive or semi-negative definite owing to monotonic conductivity changes within the lung regions. We used these monotonicity constraints to improve the quality of lung EIT imaging. We tested the proposed methods in numerical simulations, phantom experiments and human experiments.</P>
A new hybrid reconstruction method in EIT
Moon Kyung Choi,Bastian Harrach,Jin Keun Seo 한국산업응용수학회 2011 한국산업응용수학회 학술대회 논문집 Vol.6 No.1
We develop a new hybrid reconstruction method(HM) which is based on a careful analysis of the correlation between the dataset δV and the standard sensitivity matrix S. The proposed method combines the conventional linearized reconstruction method(LM) with a different method called sensitivity matrix based factorization method(S-FM). We found that the two methods are complementary to each other in the same sensitivity matrix-based system; the LM finds a best linear combination of S that produces the dataset δV, while the S-FM provides a pixel-wise index (in the imaging domain) indicating the possibility of the presence of anomaly at each pixel by estimating correlation between the dataset δV and the column vector of S corresponding to the pixel. The S-FM as a supplementary operator to LM plays two important roles; regularization and localization. We perform various numerical simulations to show that the HM effectively deal with some reconstruction artifacts in LM.
Theoretical investigation of ozone production in negative corona discharge
B. Mennad,Z. Harrache,D. Amir Aid,A. Belasri 한국물리학회 2010 Current Applied Physics Vol.10 No.6
The purpose of this work is to highlight the chemical kinetics in plasma of pure oxygen. A comprehensive model of ozone generation in wire-to-cylinder negative corona discharge is presented. The model combines the physical processes in the discharge with the chemistry of ozone formation. It is based on an extensive reaction scheme including the major electronic and ionic processes. The importance of excited atomic and molecular states is demonstrated. The obtained results show clearly that the surface material affect quite well the ozone decomposition.
Numerical investigation of gas heating effect in dielectric barrier discharge for Ne-Xe excilamp
Amar Benmoussa,Ahmed Belasri,Zahir Harrache 한국물리학회 2017 Current Applied Physics Vol.17 No.4
The purpose of this paper is to study the gas heating phenomenon in dielectric barrier discharge (DBD) due to the Joule heating effect for Ne-Xe gas mixtures. In this work, the simulationwas performed using a one-dimensional fluid model. The gas temperature profile was calculated by heat conduction equation resolution along gap distance of discharge. The increasing of gas temperature close to the vicinity of cathode is due to the high values in the power deposited in this region. The results show that the gas temperature in DBD excited with rectangular applied voltage waveform is more important than the discharge created by a sinusoidal excitation. For high values of secondary electron emission coefficient (g) the gas temperature will be increasing. The effect of varying gas mixture composition on gas temperature has been also examined.
Moon Kyung Choi,Jin Keun Seo,Bastian Harrach 한국산업응용수학회 2010 한국산업응용수학회 학술대회 논문집 Vol.5 No.1
This paper elaborates on characterization of shape and position errors in one step linear Gauss-Newton reconstruction method for electrical impedance tomography in the special case when the imaging subject has a homogeneous background with some conductivity anomalies. Although the reconstruction method using the linearized sensitivity matrix has been used widely last three decades, there is not any rigorous result about how close the reconstructed image is to the true change. Recently, two of the authors showed rigorously that the linear method in EIT does not produce position and shape errors in reconstructed images regardless the conductivity contrast across the anomaly. The theoretical result requires a continuous sampling on the boundary. In EIT system having a limited number of electrodes, there always exist shape errors; the shape errors depend mainly on the configuration of electrodes and the linearization is minor cause of the shape and position errors.
PROJECTIVE ELECTRICAL IMPEDANCE RECONSTRUCTION WITH TWO MEASUREMENTS
Munkh-Erdene Ts,Eunjung Lee,Jin Keun Seo,Bastian Harrach,Sungwhan Kim 한국산업응용수학회 2012 한국산업응용수학회 학술대회 논문집 Vol.7 No.1
This method presents a projective reconstruction method of electrical impedance distribution using two boundary measurements of current-voltage data. The proposed method has a major advantage over existing EIT systems: relatively high resolution impedance image in a nearsurface region underneath the voltage-sensing probe that is placed on a skin surface. We attach two pair of electrodes on the border of the probe in such a way that each pair of electrodes generates electrical current flowing underneath the voltage-sensing probe and two currents flow across each other. A careful analysis of the measured data with respect to local perturbation of admittivity leads to the projective reconstruction method and its rationale. Numerical simulations show that the proposed method successfully reconstructs high resolution conductivity images in a near-surface region underneath the probe.
Bioimpedance spectroscopy tensor probe for anisotropic measurements
Kwon, H.,Wi, H.,Karki, B.,Lee, E. J.,McEwan, A.,Woo, E. J.,Harrach, B.,Seo, J. K.,Oh, T. I. IET 2012 Electronics letters Vol.48 No.20
<P>The tetrapolar electrode configuration used in bioimpedance suffers from negative sensitivity and is confounded by anisotropic tissue such as blood vessels or muscle and nerve fibres. Proposed is a circular array of electrodes to focus current directly underneath the probe and provide anisotropy information. It is shown that an implementation using 16 miniature electrodes is able to outperform the tetrapolar method in sensitivity and impedance estimation. The proposed method can also recover anisotropic conductivity tensors from experiments for the first time.</P>