• Journal of Biomedical Engineering Research
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• v.25 no.3
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• pp.183-188
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• 2004

Magnetic resonance current density imaging (MRCDI) is a useful method for measuring electrical current density distribution inside an object. To avoid object rotations during the conventional MRCDI scans, we have reconstructed current density component images by applying a spatial filter to the magnetic field data measured both inside and outside the object. To measure the magnetic field outside the object with MRI, we immersed the object in a water tank. To evaluate accuracy of the current density imaging, we have made a conductivity phantom with a corresponding finite element method model. We have compared the experimentally obtained current density images with the ones calculated by the finite element method. The average errors of the reconstructed current density images were 6.6 ∼ 45.4 ％ when the injected currents were 1 ∼ 24 mA. We expect that the current density component imaging technique can be used in diverse biomedical applications such as electrical therapy system developments and biological electrical safety analysis.

• Communications of the Korean Mathematical Society
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• v.16 no.3
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• pp.519-541
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• 2001

Magnetic Resonance Electrical Impedance Tomography(MREIT) is a new medical imaging technique for the cross-sectional conductivity distribution of a human body using both EIT(Electrical Impedance Tomography) and MRI(Magnetic Resonance Imaging) system. MREIT system was designed to enhance EIT imaging system which has inherent low sensitivity of boundary measurements to any changes of internal tissue conductivity values. MREIT utilizes a recent CDI (Current Density Imaging) technique of measuring the internal current density by means of MRI technique. In this paper, a mathematical modeling for MREIT and image reconstruction method called the alternating J-substitution algorithm are presented. Computer simulations show that the alternating J-substitution algorithm provides accurate high-resolution conductivity images.

• Journal of Biomedical Engineering Research
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• v.23 no.4
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• pp.269-279
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• 2002

When we inject a current into an electrically conducting subject such as a human body, voltage and current density distributions are formed inside the subject. The current density within the subject and injection current in the lead wires generate a magnetic field. This magnetic flux density within the subject distorts phase of spin-echo magnetic resonance images. In Magnetic Resonance Current Density Imaging (MRCDI) technique, we obtain internal magnetic flux density images and produce current density images from $\bigtriangledown{\times}B/\mu_\theta$. This internal information is used in Magnetic Resonance Electrical Impedance Tomography (MREIT) where we try to reconstruct a cross-sectional resistivity image of a subject. This paper describes numerical techniques of computing voltage. current density, and magnetic flux density within a subject due to an injection current. We use the Finite Element Method (FEM) and Biot-Savart law to calculate these variables from three-dimensional models with different internal resistivity distributions. The numerical analysis techniques described in this paper are used in the design of MRCDI experiments and also image reconstruction a1gorithms for MREIT.

• Investigative Magnetic Resonance Imaging
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• v.25 no.4
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• pp.229-251
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• 2021

Arteriosclerosis is the leading cause of stroke, with a fatality rate surpassing that of ischemic heart disease. High-resolution vessel wall magnetic resonance imaging is generally recognized as a non-invasive and panoramic method for the evaluation of arterial plaque; however, this method requires improved signal-to-noise ratio and scanning speed. Recent advances in high-density head and neck coil arrays are characterized by broad coverage, multiple channels, and closefitting designs. This review analyzes fast magnetic resonance imaging from the perspective of accelerated algorithms for vessel wall imaging and demonstrates the need for effective algorithms for signal acquisition using advanced radiofrequency system. We summarize different phased-array structures under various experimental objectives and equipment conditions, introduce current research results, and propose prospective research studies in the future.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.1-6
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• 2007

Two impedance imaging systems of multi-frequency electrical impedance tomography (MFEIT) and magnetic resonance electrical impedance tomography (MREIT) are described. MFEIT utilizes boundary measurements of current-voltage data at multiple frequencies to reconstruct cross-sectional images of a complex conductivity distribution (${\sigma}+i{\omega}{\varepsilon}$) inside the human body. The inverse problem in MFEIT is ill-posed due to the nonlinearity and low sensitivity between the boundary measurement and the complex conductivity. In MFEIT, we therefore focus on time- and frequency-difference imaging with a low spatial resolution and high temporal resolution. Multi-frequency time- and frequency-difference images in the frequency range of 10 Hz to 500 kHz are presented. In MREIT, we use an MRI scanner to measure an internal distribution of induced magnetic flux density subject to an injection current. This internal information enables us to reconstruct cross-sectional images of an internal conductivity distribution with a high spatial resolution. Conductivity image of a postmortem canine brain is presented and it shows a clear contrast between gray and white matters. Clinical applications for imaging the brain, breast, thorax, abdomen, and others are briefly discussed.

• Journal of Biomedical Engineering Research
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• v.27 no.1
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• pp.30-37
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• 2006

Injecting currents into an electrically conducting subject, we may measure the induced magnetic flux density distributions using an MRI scanner. The measured data are utilized to reconstruct cross-sectional images of internal conductivity and current density distributions in Magnetic Resonance Electrical Impedance Tomography (MREIT). Injection currents are usually provided in a form of mono-polar or bi-polar pulses synchronized with an MR pulse sequence. Given an MRI scanner performing the MR phase imaging to extract the induced magnetic flux density data, the current source becomes one of the key parts determining the signal-to-noise ratio (SNR) of the measured data. Since this SNR is crucial in determining the quality of reconstructed MREIT images, special care must be given in the design and implementation of the current source. This paper describes a current source design for MREIT with features including interleaved current injection, arbitrary current waveform, electrode switching to discharge any stored charge from previous current injections, optical isolation from an MR spectrometer and PC, precise current injection timing control synchronized with any MR pulse sequence, and versatile PC control program. The performance of the current source was verified using a 3T MRI scanner and saline phantoms.

• Journal of Biomedical Engineering Research
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• v.29 no.6
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• pp.436-442
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• 2008

Magnetic resonance electrical impedance tomography(MREIT) has been suggested to produce cross-sectional conductivity images of an electrically conducting object such as the human body. In most previous studies, recessed electrodes have been used to inject imaging currents into the object. An MRI scanner was used to capture induced magnetic flux density data inside the object and a conductivity image reconstruction algorithm was applied to the data. This paper reports the performance of a thin and flexible carbon-hydrogel electrode that replaces the bulky and rigid recessed electrode in previous studies. The new carbon-hydrogel electrode produces a negligible amount of artifacts in MR and conductivity images and significantly simplifies the experimental procedure. We can fabricate the electrode in different shapes and sizes. Adding a layer of conductive adhesive, we can easily attach the electrode on an irregular surface with an excellent contact. Using a pair of carbon-hydrogel electrodes with a large contact area, we may inject an imaging current with increased amplitude primarily due to a reduced average current density underneath the electrodes. Before we apply the new electrode to a human subject, we evaluated its performance by conducting MREIT imaging experiments of five swine legs. Reconstructed conductivity images of the swine legs show a good contrast among different muscles and bones. We suggest a future study of human experiments using the carbon-hydrogel electrode following the guideline proposed in this paper.

• Korean Journal of Biological Psychiatry
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• v.19 no.2
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• pp.77-83
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• 2012

Objectives : Although there have been studies that examine sex differences of the brain structures using magnetic resonance imaging, studies that specifically investigate cerebellar structural differences between men and women are scarce. The purpose of current study was to examine sex differences in structures of the cerebellum using cerebellar template and cerebellum analysis methods. Methods : Sixteen men and twenty women were included in the study. A MATLAB based program (MathWorks, Natick, MA, USA), Statistical Parametric Mapping 5 (SPM5) using the spatially unbiased infra-tentorial atlas template (SUIT) as the cerebellum template, was used to analyze the brain imaging data. Results : There was no significant difference in age between men (mean age=28.1) and women (mean age=27.2). Men showed higher gray matter density than women in two left cerebellar areas including the clusters in the lobules IV and V (a cluster located across the lobules IV and V), and the lobule VIIIb (lobules IV and V, t=4.75, p<0.001 ; lobule VIIIb, t=3.08, p=0.004). Conclusions : The current study found differences in cerebellar gray matter density between men and women. The current study holds its significance for applying the template specifically developed for the analysis of cerebellum.

• Journal of Biomedical Engineering Research
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• v.27 no.2
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• pp.64-72
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• 2006

The present study introduces a new cortical patch-based source model for EEG/MEG cortical source imaging to consider anatomical constraints more precisely. Conventional source models for EEG/MEG cortical source imaging have used coarse cortical surface mesh or sampled small number of vertices from fine surface mesh, and thus they failed to utilize full anatomical information which nowadays we can get with sub-millimeter modeling accuracy. Conventional ones placed a single dipolar source on each cortical patch and estimated its intensity by means of various inverse algorithms; whereas the suggested cortical patch-based model integrates whole cortical area to construct lead field matrix and estimates current density that is assumed to be constant in each cortical patch. We applied the proposed and conventional models to realistic EEG data and compared the results quantitatively. The quantitative comparisons showed that the proposed model can provide more precise spatial descriptions of neuronal source distribution.

• Korean Journal of Radiology
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• v.22 no.1
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• pp.9-22
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• 2021

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is a rapid, unenhanced imaging technique that measures the motion of water molecules within tissues and provides information regarding the cell density and tissue microstructure. DW MRI has demonstrated the potential to improve the specificity of breast MRI, facilitate the evaluation of tumor response to neoadjuvant chemotherapy and can be employed in unenhanced MRI screening. However, standardization of the acquisition and interpretation of DW MRI is challenging. Recently, the European Society of Breast Radiology issued a consensus statement, which described the acquisition parameters and interpretation of DW MRI. The current article describes the basic principles, standardized acquisition protocols and interpretation guidelines, and the clinical applications of DW MRI in breast imaging.