The Impact of Anisotropy on the Accuracy of Conductivity Imaging: A Quantitative Validation Study.

We present a quantitative validation study to assess the accuracy of low-frequency conductivity imaging methods, based on a testing current measured using Current Density Imaging (CDI). We tested the proposed procedure to study the influence of tissue anisotropy on the accuracy of conductivity reconstruction methods, using a finite element model of anisotropic brain tissue. Simulations were carried out for three different levels of tissue anisotropy to compare the results obtained by our recently developed anisotropic conductivity method with those obtained by our well-established conductivity method that assumes isotropic conductivity.

Experimental implementation of a new method of imaging anisotropic electric conductivities.

This paper presents the first experiment of imaging anisotropic impedance using a novel technique called Diffusion Tensor Current Density Impedance Imaging (DTCD-II). A biological anisotropic tissue phantom was constructed and an experimental implementation of the new method was performed. The results show that DT-CD-II is an effective way of non-invasively measuring anisotropic conductivity in biological media.

Polar decomposition radio-frequency current density imaging.

Polar Decomposition Radio-frequency Current Density Imaging (PD-RFCDI) is an imaging technique that non-invasively measures RF current density components inside a sample using MRI. Previous PD-RFCDI implementations suffer from the strict constraint on the amount of applied current as well as severe interference from the unwanted induced current. This work proposes solutions to both problems which successfully remove the current constraints of PD-RFCDI.

Radio-frequency current density imaging based on a 180 (°) sample rotation with feasibility study of full current density vector reconstruction.

Radio-frequency current density imaging (RF-CDI) is a technique that noninvasively measures current density distributions at the Larmor frequency utilizing magnetic resonance imaging. Previously implemented RF-CDI methods reconstruct the applied current density component J(z) along the static magnetic field of the imager [(B)\vec](0) (the z direction) based on the assumption that the z-directional change of the magnetic field component H(z) can be ignored compared to J(z). However, this condition may be easily violated in biomedical applications.

In-vivo measurement of relationship between applied current amplitude and current density magnitude from 10 mA to 110 mA.

Current density imaging (CDI) is a magnetic resonance imaging (MRI) technique used to quantitatively measure current density vectors throughout the volume of an object/subject placed in the MRI system. Electrical current pulses are applied externally to the object/subject and are synchronized with the MRI sequence. In this work, CDI is used to measure average current density magnitude in the torso region of an in-vivo piglet for applied current pulse amplitudes ranging from 10 mA to 110 mA.

Measurement of current density vectors in a live pig for the study of human electro-muscular incapacitation devices.

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.

Multislice radio-frequency current density imaging.

Radio-frequency current density imaging (RF-CDI) is an imaging technique that noninvasively measures current density distribution at the Larmor frequency utilizing magnetic resonance imaging (MRI). Previously implemented RF-CDI techniques were only able to image a single slice transverse to the static magnetic field B(0) . This paper describes the first realization of a multislice RF-CDI sequence on a 1.

Current density impedance imaging.

Current density impedance imaging (CDII) is a new impedance imaging technique that can noninvasively measure the conductivity distribution inside a medium. It utilizes current density vector measurements which can be made using a magnetic resonance imager (MRI) (Scott , 1991). CDII is based on a simple mathematical expression for inverted Delta sigma / sigma = inverted Delta ln sigma, the gradient of the logarithm of the conductivity sigma, at each point in a region where two current density vectors J1 and J2 have been measured and J1 x J2 not equal 0.

Gradient distortion correction for low frequency current density imaging.

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.

MR current density and conductivity imaging: the state of the art.

Current density imaging (CDI) is an imaging technique that measures electrical current density distributions in a volume of material or tissue, which can be imaged using magnetic resonance imaging (MRI). Measurements of current density are obtained by applying an external current to the material/tissue during an MRI acquisition. The magnetic fields produced by the applied current are mapped onto the phase image of the MRI acquisition.

Current density imaging and electrically induced skin burns under surface electrodes.

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, and used low-frequency current density imaging (LFCDI) to determine the current density (CD) distribution through the skin before and after burns were induced by application of electrical current (200 Hz, 70% duty cycle, 20-35 mA monophasic square waveform applied to the electrodes for 30-135 min). The regions of increased CD correlate well with the gross morphological changes (burns) observed.

Measurement of thoracic current flow in pigs for the study of defibrillation and cardioversion.

Although defibrillation has been in clinical use for more than 50 years, the complete current flow distribution inside the body during a defibrillation procedure has never been directly measured. This is due to the lack of appropriate imaging technology to noninvasively monitor the current flow inside the body. The current density imaging (CDI) technique, using a magnetic resonance (MR) imager, provides a new approach to this problem [Scott et al.

Why does MTR change with neuronal depolarization?

T1 and T2 relaxation, and magnetization transfer (MT) of the rat brain were measured during experimentally induced spreading depression (SD). All measured MR parameters changed during SD: T1 relaxation increased by approximately 13%, whereas the T2 increase was substantially larger (88%). MT results showed an MT ratio (MTR) decrease of 9%.