Aps Ohio Sections Fall Meeting Abstracts, Oct 1, 2004
Magnetic Resonance Imaging (MRI) can be used to generate Current Density Images (CDI) that contai... more Magnetic Resonance Imaging (MRI) can be used to generate Current Density Images (CDI) that contain the current density vectors at all points in an imaged volume. CDI works because MRI images are complex and the phase of a given pixel is proportional to the magnetic field induced by the current being imaged. To find the three vector components of the induced magnetic field a subject must be imaged in three orthogonal orientations. The current density vectors can then be computed from the induced magnetic field using Maxwell's equation. CDI was performed on pigs hearts in-vivo using current applied by electrodes in a defibrillation arrangement. The current density streamlines were calculated and superimposed over the anatomical images of the pigs heart and they suggest known myocardial fiber orientations. Current density imaging is also being employed for an ongoing investigation into deep brain stimulating electrodes in order to investigate the electrodes therapeutic function.
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439), 2003
Current density imaging (CDI) using a magnetic resonance (MR) imager has been shown to accurately... more Current density imaging (CDI) using a magnetic resonance (MR) imager has been shown to accurately measure electrical current density in a conductive object. CDI measures the magnetic field generated by the current and converts it to current density (CD) by computing its curl. Therefore, CDI avoids both the inverse problem and invasiveness of other electrical measurement techniques such as electrical
Designers of gel-type surface electrodes, used in medical applications such as pain relief and ne... more Designers of gel-type surface electrodes, used in medical applications such as pain relief and neuromuscular stimulation, require a more thorough understanding of current pathways in tissue in order to design more effective electrical stimulation systems. To investigate these pathways, a finite element model (FEM) was used to compute current density distributions produced by an electrode placed on the surface of a homogeneous, tissue-mimicking gel slab. The gel slab phantom was constructed and the current densities were measured using a recently developed technique called current density imaging (CDI). CDI uses the phase data produced by magnetic resonance imaging (MRI) as a measure of the magnetic fields produced by the externally applied current. The results of the FEM simulation and CDI measurements compare well. CDI has several potential advantages over conventional FEM techniques including: no requirement for knowledge of local tissue conductivities, low and constant computatio...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004
Current density imaging (CDI) is an MRI technique used to measure electrical current density vect... more Current density imaging (CDI) is an MRI technique used to measure electrical current density vectors throughout a volume of tissue. Previous work used CDI to measure current pathways through the heart and chest of a post-mortem pig when current is applied using external flexible defibrillation electrodes with typical anterior-anterior positioning. In these post-mortem studies, current pathways were probably influenced by the anisotropic conductivity of the tissues. This work aims to compare post-mortem ( approximately 15 min. and approximately 1 hour after death) results with new in vivo CDI measurements. These measurements indicate that the macroscopic (i.e. across the whole body) current pathways remain similar before and after death, however, at a smaller scale (i.e. distances of a few cm) current pathways are different, particularly in the heart. This comparison demonstrates the influence on current pathways of rapidly changing electric properties of tissue following death.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2006
Radio frequency current density imaging (RF-CDI) is an imaging technique that measures current de... more Radio frequency current density imaging (RF-CDI) is an imaging technique that measures current density distribution at the Larmor frequency utilizing magnetic resonance imaging (MRI). The multi-slice RF-CDI sequence has extended the ability of RF-CDI to image multiple slices and thus has enhanced its capacity for biomedical applications. In this paper, the influence of MRI random noise on the sensitivity of multi-slice RF-CDI measurement is studied. The formula of current noise is derived, which is verified by both simulation and phantom experiments. A 3-D finite-difference time-domain (FDTD) model is employed to compute the electromagnetic fields in the simulation.
2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2001
The origin of electrical burns under gel-type surface electrodes is a controversial topic that is... more The origin of electrical burns under gel-type surface electrodes is a controversial topic that is not well understood. To investigate the phenomenon, we have developed an excised porcine skin+gel model. In the present paper, we describe methods to detect these burns in the skin+gel model in an effort to understand the genesis of these burns. Burns were induced by severe electrical stimulation and changes in the impedance spectra and current density measured. We found that the changes in impedance spectrum were characterized by significant drop in the low frequency (<1 kHz) impedance magnitude and the formation of welts in the skin. Low frequency current density imaging (LFCDI) revealed regions of high current density beneath the electrode before burns were induced suggesting the possibility of predicting the locations where welts from burns will form and the importance of current density and local tissue impedance in the formation of these burns.
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
Current density imaging (CDI) is a technique that uses magnetic resonance imaging (MRI) to measur... more Current density imaging (CDI) is a technique that uses magnetic resonance imaging (MRI) to measure the distribution of externally applied electric current inside tissues. However, GDI processing is rendered inaccurate by the distortion caused by the nonlinearity of MRI gradient fields. The distortion interferes with the proper registration and the curl operation required for correct computation of current density vectors. To address this problem, a calibration phantom was imaged to determine the distortion and to generate calibration maps to correct the distorted current density images. A validation experiment involving a cylindrical phantom was performed to verify this method. Comparison of the distorted and corrected images reveals that both the registration and the curl operation are successfully corrected by this method.
2007 Joint Meeting of the 6th International Symposium on Noninvasive Functional Source Imaging of the Brain and Heart and the International Conference on Functional Biomedical Imaging, 2007
is an imaging technique that measures current density distribution at the Larmor frequency utiliz... more is an imaging technique that measures current density distribution at the Larmor frequency utilizing magnetic resonance imaging (MRI). The previous implemented RF current reconstruction method is based on the single orientation condition that usually requires the applied current flowing mainly in the direction of the static magnetic field of the MR imager. However, this condition can be violated in biomedical applications. This paper proposes a new reconstruction method for RF-CDI, which does not rely on the single orientation assumption. Instead, the sample is rotated 180 degrees to collect MR data from two opposite orientations. Simulations and experiment are analyzed for the feasibility of the approach.
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
Current density imaging (CDI) is an MRI technique used to quantitatively measure current density ... more Current density imaging (CDI) is an MRI technique used to quantitatively measure current density vectors in biological tissue. A fast CDI sequence was developed that can image the whole body of a 4 kg pig in about 15 minutes. A state of ventricular fibrillation (VF) can be sustained for nearly 30 minutes allowing two complete CDI scans of the same subject. A single parameter, i.e. electrode position, is adjusted between the two scans for comparative analysis. This study compares the current density vector directions and current density magnitudes measured for two typical electrode positions, i.e. apex anterior (AA) and apex posterior (AP). The comparative experiment is repeated on the same subjects for states of immediate post-mortem and one hour post-mortem. Further, the acquired vector datasets are used to compute conductivity images of the heart.
2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2008
Current density imaging (CDI) is an MRI technique used to quantitatively measure current density ... more Current density imaging (CDI) is an MRI technique used to quantitatively measure current density vectors in biological tissue. A CDI sequence and corresponding experimental method were developed for the study of human electro-muscular incapacitation (HEMI) devices using an animal model. Measurements of current density vectors were performed in piglets weighing 4 to 5 kg. Pathways of current density vectors in the region of the chest and heart were investigated using vector plotting and streamline integration methods. Measurement of current density vectors were also used to analyze the relationship between applied current amplitude and measured current density magnitude in the range of 10 mA to 45 mA of applied current.
2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009
Current density and electrical conductivity imaging research at the University of Toronto is revi... more Current density and electrical conductivity imaging research at the University of Toronto is reviewed. Methods for imaging live animals at low frequency are described and contrasted with EIT and other MRI based techniques. New work on imaging at radio frequencies is presented and future work directions are discussed. It is concluded that low frequency methods are mature and ready for application in small animals and that radio frequency methods will soon have application in small animals.
Aps Ohio Sections Fall Meeting Abstracts, Oct 1, 2004
Magnetic Resonance Imaging (MRI) can be used to generate Current Density Images (CDI) that contai... more Magnetic Resonance Imaging (MRI) can be used to generate Current Density Images (CDI) that contain the current density vectors at all points in an imaged volume. CDI works because MRI images are complex and the phase of a given pixel is proportional to the magnetic field induced by the current being imaged. To find the three vector components of the induced magnetic field a subject must be imaged in three orthogonal orientations. The current density vectors can then be computed from the induced magnetic field using Maxwell's equation. CDI was performed on pigs hearts in-vivo using current applied by electrodes in a defibrillation arrangement. The current density streamlines were calculated and superimposed over the anatomical images of the pigs heart and they suggest known myocardial fiber orientations. Current density imaging is also being employed for an ongoing investigation into deep brain stimulating electrodes in order to investigate the electrodes therapeutic function.
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439), 2003
Current density imaging (CDI) using a magnetic resonance (MR) imager has been shown to accurately... more Current density imaging (CDI) using a magnetic resonance (MR) imager has been shown to accurately measure electrical current density in a conductive object. CDI measures the magnetic field generated by the current and converts it to current density (CD) by computing its curl. Therefore, CDI avoids both the inverse problem and invasiveness of other electrical measurement techniques such as electrical
Designers of gel-type surface electrodes, used in medical applications such as pain relief and ne... more Designers of gel-type surface electrodes, used in medical applications such as pain relief and neuromuscular stimulation, require a more thorough understanding of current pathways in tissue in order to design more effective electrical stimulation systems. To investigate these pathways, a finite element model (FEM) was used to compute current density distributions produced by an electrode placed on the surface of a homogeneous, tissue-mimicking gel slab. The gel slab phantom was constructed and the current densities were measured using a recently developed technique called current density imaging (CDI). CDI uses the phase data produced by magnetic resonance imaging (MRI) as a measure of the magnetic fields produced by the externally applied current. The results of the FEM simulation and CDI measurements compare well. CDI has several potential advantages over conventional FEM techniques including: no requirement for knowledge of local tissue conductivities, low and constant computatio...
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2004
Current density imaging (CDI) is an MRI technique used to measure electrical current density vect... more Current density imaging (CDI) is an MRI technique used to measure electrical current density vectors throughout a volume of tissue. Previous work used CDI to measure current pathways through the heart and chest of a post-mortem pig when current is applied using external flexible defibrillation electrodes with typical anterior-anterior positioning. In these post-mortem studies, current pathways were probably influenced by the anisotropic conductivity of the tissues. This work aims to compare post-mortem ( approximately 15 min. and approximately 1 hour after death) results with new in vivo CDI measurements. These measurements indicate that the macroscopic (i.e. across the whole body) current pathways remain similar before and after death, however, at a smaller scale (i.e. distances of a few cm) current pathways are different, particularly in the heart. This comparison demonstrates the influence on current pathways of rapidly changing electric properties of tissue following death.
Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2006
Radio frequency current density imaging (RF-CDI) is an imaging technique that measures current de... more Radio frequency current density imaging (RF-CDI) is an imaging technique that measures current density distribution at the Larmor frequency utilizing magnetic resonance imaging (MRI). The multi-slice RF-CDI sequence has extended the ability of RF-CDI to image multiple slices and thus has enhanced its capacity for biomedical applications. In this paper, the influence of MRI random noise on the sensitivity of multi-slice RF-CDI measurement is studied. The formula of current noise is derived, which is verified by both simulation and phantom experiments. A 3-D finite-difference time-domain (FDTD) model is employed to compute the electromagnetic fields in the simulation.
2001 Conference Proceedings of the 23rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2001
The origin of electrical burns under gel-type surface electrodes is a controversial topic that is... more The origin of electrical burns under gel-type surface electrodes is a controversial topic that is not well understood. To investigate the phenomenon, we have developed an excised porcine skin+gel model. In the present paper, we describe methods to detect these burns in the skin+gel model in an effort to understand the genesis of these burns. Burns were induced by severe electrical stimulation and changes in the impedance spectra and current density measured. We found that the changes in impedance spectrum were characterized by significant drop in the low frequency (<1 kHz) impedance magnitude and the formation of welts in the skin. Low frequency current density imaging (LFCDI) revealed regions of high current density beneath the electrode before burns were induced suggesting the possibility of predicting the locations where welts from burns will form and the importance of current density and local tissue impedance in the formation of these burns.
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
Current density imaging (CDI) is a technique that uses magnetic resonance imaging (MRI) to measur... more Current density imaging (CDI) is a technique that uses magnetic resonance imaging (MRI) to measure the distribution of externally applied electric current inside tissues. However, GDI processing is rendered inaccurate by the distortion caused by the nonlinearity of MRI gradient fields. The distortion interferes with the proper registration and the curl operation required for correct computation of current density vectors. To address this problem, a calibration phantom was imaged to determine the distortion and to generate calibration maps to correct the distorted current density images. A validation experiment involving a cylindrical phantom was performed to verify this method. Comparison of the distorted and corrected images reveals that both the registration and the curl operation are successfully corrected by this method.
2007 Joint Meeting of the 6th International Symposium on Noninvasive Functional Source Imaging of the Brain and Heart and the International Conference on Functional Biomedical Imaging, 2007
is an imaging technique that measures current density distribution at the Larmor frequency utiliz... more is an imaging technique that measures current density distribution at the Larmor frequency utilizing magnetic resonance imaging (MRI). The previous implemented RF current reconstruction method is based on the single orientation condition that usually requires the applied current flowing mainly in the direction of the static magnetic field of the MR imager. However, this condition can be violated in biomedical applications. This paper proposes a new reconstruction method for RF-CDI, which does not rely on the single orientation assumption. Instead, the sample is rotated 180 degrees to collect MR data from two opposite orientations. Simulations and experiment are analyzed for the feasibility of the approach.
2006 International Conference of the IEEE Engineering in Medicine and Biology Society, 2006
Current density imaging (CDI) is an MRI technique used to quantitatively measure current density ... more Current density imaging (CDI) is an MRI technique used to quantitatively measure current density vectors in biological tissue. A fast CDI sequence was developed that can image the whole body of a 4 kg pig in about 15 minutes. A state of ventricular fibrillation (VF) can be sustained for nearly 30 minutes allowing two complete CDI scans of the same subject. A single parameter, i.e. electrode position, is adjusted between the two scans for comparative analysis. This study compares the current density vector directions and current density magnitudes measured for two typical electrode positions, i.e. apex anterior (AA) and apex posterior (AP). The comparative experiment is repeated on the same subjects for states of immediate post-mortem and one hour post-mortem. Further, the acquired vector datasets are used to compute conductivity images of the heart.
2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2008
Current density imaging (CDI) is an MRI technique used to quantitatively measure current density ... more Current density imaging (CDI) is an MRI technique used to quantitatively measure current density vectors in biological tissue. A CDI sequence and corresponding experimental method were developed for the study of human electro-muscular incapacitation (HEMI) devices using an animal model. Measurements of current density vectors were performed in piglets weighing 4 to 5 kg. Pathways of current density vectors in the region of the chest and heart were investigated using vector plotting and streamline integration methods. Measurement of current density vectors were also used to analyze the relationship between applied current amplitude and measured current density magnitude in the range of 10 mA to 45 mA of applied current.
2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009
Current density and electrical conductivity imaging research at the University of Toronto is revi... more Current density and electrical conductivity imaging research at the University of Toronto is reviewed. Methods for imaging live animals at low frequency are described and contrasted with EIT and other MRI based techniques. New work on imaging at radio frequencies is presented and future work directions are discussed. It is concluded that low frequency methods are mature and ready for application in small animals and that radio frequency methods will soon have application in small animals.
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