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Ohin Kwon - One of the best experts on this subject based on the ideXlab platform.

  • magnetic resonance Electrical Impedance Tomography at 3 tesla field strength
    Magnetic Resonance in Medicine, 2004
    Co-Authors: Byung Il Lee, Eung Je Woo, Jin Keun Seo, Tae S Park, Soo Yeol Lee, Min H Cho, Ohin Kwon
    Abstract:

    Magnetic resonance Electrical Impedance Tomography (MREIT) is a recently developed imaging technique that combines MRI and Electrical Impedance Tomography (EIT). In MREIT, cross-sectional Electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an Electrically conducting object when an Electrical current is injected into the object. In this work we present the results of Electrical conductivity imaging experiments, and performance evaluations of MREIT in terms of noise characteristics and spatial resolution. The MREIT experiment was performed with a 3.0 Tesla MRI system on a phantom with an inhomogeneous conductivity distribution. We reconstructed the conductivity images in a 128 × 128 matrix format by applying the harmonic Bz algorithm to the z-component of the internal magnetic field density data. Since the harmonic Bz algorithm uses only a single component of the internal magnetic field data, it was not necessary to rotate the object in the MRI scan. The root mean squared (RMS) errors of the reconstructed images were between 11% and 35% when the injection current was 24 mA. Magn Reson Med 51:1292–1296, 2004. © 2004 Wiley-Liss, Inc.

  • magnetic resonance Electrical Impedance Tomography mreit simulation study of j substitution algorithm
    IEEE Transactions on Biomedical Engineering, 2002
    Co-Authors: Ohin Kwon, Jeongrock Yoon
    Abstract:

    We developed a new image reconstruction algorithm for magnetic resonance Electrical Impedance Tomography (MREIT). MREIT is a new EIT imaging technique integrated into magnetic resonance imaging (MRI) system. Based on the assumption that internal current density distribution is obtained using magnetic resonance imaging (MRI) technique, the new image reconstruction algorithm called J-substitution algorithm produces cross-sectional static images of resistivity (or conductivity) distributions. Computer simulations show that the spatial resolution of resistivity image is comparable to that of MRI. MREIT provides accurate high-resolution cross-sectional resistivity images making resistivity values of various human tissues available for many biomedical applications.

  • equipotential line method for magnetic resonance Electrical Impedance Tomography
    Inverse Problems, 2002
    Co-Authors: Ohin Kwon, Jeongrock Yoon
    Abstract:

    We consider magnetic resonance Electrical Impedance Tomography, which aims to reconstruct the conductivity distribution using the internal current density furnished by magnetic resonance imaging. We show the uniqueness of the conductivity reconstruction with one measurement imposing the Dirichlet boundary condition. We also propose a fast non-iterative numerical algorithm for the conductivity reconstruction using the internal current vector information. The algorithm is mainly based on efficient numerical construction of equipotential lines. The resulting numerical method is stable in the sense that the error of the computed conductivity is linearly proportional to the input noise level and the introduction of internal current data makes the Impedance Tomography problem well-posed. We present various numerical examples to show the feasibility of using our method.

Eung Je Woo - One of the best experts on this subject based on the ideXlab platform.

  • magnetic resonance Electrical Impedance Tomography mreit
    Siam Review, 2011
    Co-Authors: Jin Keun Seo, Eung Je Woo
    Abstract:

    Magnetic resonance Electrical Impedance Tomography (MREIT) is a recently developed medical imaging modality visualizing conductivity images of an Electrically conducting object. MREIT was motivated by the well-known ill-posedness of the image reconstruction problem of Electrical Impedance Tomography (EIT). Numerous experiences have shown that practically measurable data sets in an EIT system are insufficient for a robust reconstruction of a high-resolution static conductivity image due to its ill-posed nature and the influences of errors in forward modeling. To overcome the inherent ill-posed characteristics of EIT, the MREIT system was proposed in the early 1990s to use the internal data of magnetic flux density ${\bf B}=(B_x,B_y,B_z)$, which is induced by an externally injected current. MREIT uses an MRI scanner as a tool to measure the $z$-component $B_z$ of the magnetic flux density, where $z$ is the axial magnetization direction of the MRI scanner. In 2001, a constructive $B_z$-based MREIT algorithm called the harmonic $B_z$ algorithm was developed and its numerical simulations showed that high-resolution conductivity image reconstructions are possible. This novel algorithm is based on the key observation that the Laplacian $\Delta B_z$ probes changes in the log of the conductivity distribution along any equipotential curve having its tangent to the vector field ${\bf J}\times (0,0,1)$, where ${\bf J}=(J_x,J_y,J_z)$ is the induced current density vector. Since then, imaging techniques in MREIT have advanced rapidly and have now reached the stage of in vivo animal and human experiments. This paper reviews MREIT from its mathematical framework to the most recent human experiment outcomes.

  • magnetic resonance Electrical Impedance Tomography at 3 tesla field strength
    Magnetic Resonance in Medicine, 2004
    Co-Authors: Byung Il Lee, Eung Je Woo, Jin Keun Seo, Tae S Park, Soo Yeol Lee, Min H Cho, Ohin Kwon
    Abstract:

    Magnetic resonance Electrical Impedance Tomography (MREIT) is a recently developed imaging technique that combines MRI and Electrical Impedance Tomography (EIT). In MREIT, cross-sectional Electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an Electrically conducting object when an Electrical current is injected into the object. In this work we present the results of Electrical conductivity imaging experiments, and performance evaluations of MREIT in terms of noise characteristics and spatial resolution. The MREIT experiment was performed with a 3.0 Tesla MRI system on a phantom with an inhomogeneous conductivity distribution. We reconstructed the conductivity images in a 128 × 128 matrix format by applying the harmonic Bz algorithm to the z-component of the internal magnetic field density data. Since the harmonic Bz algorithm uses only a single component of the internal magnetic field data, it was not necessary to rotate the object in the MRI scan. The root mean squared (RMS) errors of the reconstructed images were between 11% and 35% when the injection current was 24 mA. Magn Reson Med 51:1292–1296, 2004. © 2004 Wiley-Liss, Inc.

  • finite element modeling of electrode skin contact Impedance in Electrical Impedance Tomography
    IEEE Transactions on Biomedical Engineering, 1993
    Co-Authors: P Hua, Eung Je Woo, John G Webster, W J Tompkins
    Abstract:

    In Electrical Impedance Tomography (EIT), the measured voltages are sensitive to electrode-skin contact Impedance because the contact Impedance and the current density through it are both high. Large electrodes were used to provide a more uniform current distribution and reduce the contact Impedance. A large electrode differs from a point electrode in that it has shunting and edge effects that cannot be modeled by a single resistor. The finite-element method (FEM) was used to study the electric field distributions underneath an electrode, and three models were developed: a FEM model, a simplified FEM model, and a weighted load model. The FEM models considered both shunting and edge effects and closely matched the experimental measurements. It is concluded that FEM models of electrodes can be used to improve the performance of an Electrical Impedance Tomography reconstruction algorithm. >

Jin Keun Seo - One of the best experts on this subject based on the ideXlab platform.

  • mathematical framework for abdominal Electrical Impedance Tomography to assess fatness
    Siam Journal on Imaging Sciences, 2017
    Co-Authors: Habib Ammari, Hyeuknam Kwon, Seungri Lee, Jin Keun Seo
    Abstract:

    This paper presents a static Electrical Impedance Tomography (EIT) technique that evaluates abdominal obesity by estimating the thickness of subcutaneous fat. EIT has a fundamental drawback for absolute admittivity imaging because of its lack of reference data for handling the forward modeling errors. To reduce the effect of boundary geometry errors in imaging abdominal fat, we develop a depth-based reconstruction method that uses a specially chosen current pattern to construct reference-like data, which are then used to identify the border between subcutaneous fat and muscle. The performance of the proposed method is demonstrated by numerical simulations using 32-channel EIT system and a humanlike domain.

  • monotonicity based Electrical Impedance Tomography for lung imaging
    arXiv: Quantitative Methods, 2017
    Co-Authors: Liangdong Zhou, Bastian Harrach, Jin Keun Seo
    Abstract:

    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 this monotonicity constraints to improve the quality of lung EIT imaging. We tested the proposed methods in numerical simulations, phantom experiments and human experiments.

  • magnetic resonance Electrical Impedance Tomography mreit
    Siam Review, 2011
    Co-Authors: Jin Keun Seo, Eung Je Woo
    Abstract:

    Magnetic resonance Electrical Impedance Tomography (MREIT) is a recently developed medical imaging modality visualizing conductivity images of an Electrically conducting object. MREIT was motivated by the well-known ill-posedness of the image reconstruction problem of Electrical Impedance Tomography (EIT). Numerous experiences have shown that practically measurable data sets in an EIT system are insufficient for a robust reconstruction of a high-resolution static conductivity image due to its ill-posed nature and the influences of errors in forward modeling. To overcome the inherent ill-posed characteristics of EIT, the MREIT system was proposed in the early 1990s to use the internal data of magnetic flux density ${\bf B}=(B_x,B_y,B_z)$, which is induced by an externally injected current. MREIT uses an MRI scanner as a tool to measure the $z$-component $B_z$ of the magnetic flux density, where $z$ is the axial magnetization direction of the MRI scanner. In 2001, a constructive $B_z$-based MREIT algorithm called the harmonic $B_z$ algorithm was developed and its numerical simulations showed that high-resolution conductivity image reconstructions are possible. This novel algorithm is based on the key observation that the Laplacian $\Delta B_z$ probes changes in the log of the conductivity distribution along any equipotential curve having its tangent to the vector field ${\bf J}\times (0,0,1)$, where ${\bf J}=(J_x,J_y,J_z)$ is the induced current density vector. Since then, imaging techniques in MREIT have advanced rapidly and have now reached the stage of in vivo animal and human experiments. This paper reviews MREIT from its mathematical framework to the most recent human experiment outcomes.

  • magnetic resonance Electrical Impedance Tomography at 3 tesla field strength
    Magnetic Resonance in Medicine, 2004
    Co-Authors: Byung Il Lee, Eung Je Woo, Jin Keun Seo, Tae S Park, Soo Yeol Lee, Min H Cho, Ohin Kwon
    Abstract:

    Magnetic resonance Electrical Impedance Tomography (MREIT) is a recently developed imaging technique that combines MRI and Electrical Impedance Tomography (EIT). In MREIT, cross-sectional Electrical conductivity images are reconstructed from the internal magnetic field density data produced inside an Electrically conducting object when an Electrical current is injected into the object. In this work we present the results of Electrical conductivity imaging experiments, and performance evaluations of MREIT in terms of noise characteristics and spatial resolution. The MREIT experiment was performed with a 3.0 Tesla MRI system on a phantom with an inhomogeneous conductivity distribution. We reconstructed the conductivity images in a 128 × 128 matrix format by applying the harmonic Bz algorithm to the z-component of the internal magnetic field density data. Since the harmonic Bz algorithm uses only a single component of the internal magnetic field data, it was not necessary to rotate the object in the MRI scan. The root mean squared (RMS) errors of the reconstructed images were between 11% and 35% when the injection current was 24 mA. Magn Reson Med 51:1292–1296, 2004. © 2004 Wiley-Liss, Inc.

Jeongrock Yoon - One of the best experts on this subject based on the ideXlab platform.

  • magnetic resonance Electrical Impedance Tomography mreit simulation study of j substitution algorithm
    IEEE Transactions on Biomedical Engineering, 2002
    Co-Authors: Ohin Kwon, Jeongrock Yoon
    Abstract:

    We developed a new image reconstruction algorithm for magnetic resonance Electrical Impedance Tomography (MREIT). MREIT is a new EIT imaging technique integrated into magnetic resonance imaging (MRI) system. Based on the assumption that internal current density distribution is obtained using magnetic resonance imaging (MRI) technique, the new image reconstruction algorithm called J-substitution algorithm produces cross-sectional static images of resistivity (or conductivity) distributions. Computer simulations show that the spatial resolution of resistivity image is comparable to that of MRI. MREIT provides accurate high-resolution cross-sectional resistivity images making resistivity values of various human tissues available for many biomedical applications.

  • equipotential line method for magnetic resonance Electrical Impedance Tomography
    Inverse Problems, 2002
    Co-Authors: Ohin Kwon, Jeongrock Yoon
    Abstract:

    We consider magnetic resonance Electrical Impedance Tomography, which aims to reconstruct the conductivity distribution using the internal current density furnished by magnetic resonance imaging. We show the uniqueness of the conductivity reconstruction with one measurement imposing the Dirichlet boundary condition. We also propose a fast non-iterative numerical algorithm for the conductivity reconstruction using the internal current vector information. The algorithm is mainly based on efficient numerical construction of equipotential lines. The resulting numerical method is stable in the sense that the error of the computed conductivity is linearly proportional to the input noise level and the introduction of internal current data makes the Impedance Tomography problem well-posed. We present various numerical examples to show the feasibility of using our method.

Inez Frerichs - One of the best experts on this subject based on the ideXlab platform.

  • cross sectional changes in lung volume measured by Electrical Impedance Tomography are representative for the whole lung in ventilated preterm infants
    Critical Care Medicine, 2014
    Co-Authors: Pauline S Van Der Burg, Inez Frerichs, Martijn Miedema, Franciscus H C De Jongh, A H Van Kaam
    Abstract:

    Objective: Electrical Impedance Tomography measures lung volume in a cross-sectional slice of the lung. Whether these cross-sectional volume changes are representative of the whole lung has only been investigated in adults, showing conflicting results. This study aimed to compare cross-sectional and whole lung volume changes using Electrical Impedance Tomography and respiratory inductive plethysmography. Design: A prospective, single-center, observational, nonrandomized study. Setting: The study was conducted in a neonatal ICU in the Netherlands. Patients: High-frequency ventilated preterm infants with respiratory distress syndrome. Interventions: Cross-sectional and whole lung volume changes were continuously and simultaneously measured by, respectively, Electrical Impedance Tomography and respiratory inductive plethysmography during a stepwise recruitment procedure. End-expiratory lung volume changes were assessed by mapping the inflation and deflation limbs using both the pressure/Impedance and pressure/inductance pairs and characterized by calculating the inflection points. In addition, oscillatory tidal volume changes were assessed at each pressure step. Measurements and Main Results: Twenty-three infants were included in the study. Of these, eight infants had to be excluded because the quality of the registration was insufficient for analysis (two Electrical Impedance Tomography and six respiratory inductive plethysmography). In the remaining 15 infants (gestational age 28.0 ± 2.6 wk; birth weight 1,027 ± 514 g), end-expiratory lung volume changes measured by Electrical Impedance Tomography were significantly correlated to respiratory inductive plethysmography measurements in 12 patients (mean r = 0.93 ± 0.05). This was also true for the upper inflection point on the inflation (r = 0.91, p < 0.01) and deflation limb (r = 0.83, p < 0.01). In 13 patients, Impedance and inductance data also correlated significantly on oscillatory tidal volume/pressure relationships (mean r = 0.81 ± 0.18). Conclusions: This study shows that cross-sectional lung volume changes measured by Electrical Impedance Tomography are representative for the whole lung and that this concept also applies to newborn infants.

  • spatial and temporal heterogeneity of regional lung ventilation determined by Electrical Impedance Tomography during pulmonary function testing
    Journal of Applied Physiology, 2012
    Co-Authors: Barbara Vogt, Gunnar Elke, Norbert Weiler, Sven Pulletz, Zhanqi Zhao, P Zabel, Inez Frerichs
    Abstract:

    Electrical Impedance Tomography (EIT) is a functional imaging modality capable of tracing continuously regional pulmonary gas volume changes. The aim of our study was to determine if EIT was able t...

  • peep titration guided by ventilation homogeneity a feasibility study using Electrical Impedance Tomography
    Critical Care, 2010
    Co-Authors: Inez Frerichs, Zhanqi Zhao, Daniel Steinmann, J Guttmann, Knut Moller
    Abstract:

    Introduction Lung protective ventilation requires low tidal volume and suitable positive end-expiratory pressure (PEEP). To date, few methods have been accepted for clinical use to set the appropriate PEEP. The aim of this study was to test the feasibility of PEEP titration guided by ventilation homogeneity using the global inhomogeneity (GI) index based on Electrical Impedance Tomography (EIT) images.

  • evaluation of an Electrical Impedance Tomography based global inhomogeneity index for pulmonary ventilation distribution
    Intensive Care Medicine, 2009
    Co-Authors: Inez Frerichs, Zhanqi Zhao, Knut Moller, Daniel Steinmann, J Guttmann
    Abstract:

    Purpose To evaluate the plausibility, stability, and interindividual comparability of the global inhomogeneity index (GI) based on Electrical Impedance Tomography (EIT).

  • assessment of changes in distribution of lung perfusion by Electrical Impedance Tomography
    Respiration, 2009
    Co-Authors: Inez Frerichs, Gunnar Elke, Sven Pulletz, Florian Reifferscheid, Dirk Schadler, Jens Scholz, Norbert Weiler
    Abstract:

    Background: Electrical Impedance Tomography (EIT) is able to detect variations in regional lung Electrical Impedance associated with changes in both air and blood content and potent