Induced current magnetic resonance electrical impedance tomography (ICMREIT) with low frequency switching of gradient fields

Eroğlu, Hasan Hüseyin
In this thesis, it is aimed to investigate induced current magnetic resonance electrical impedance tomography (ICMREIT) starting from modeling and analysis to experimental validation. Forward and inverse problems of ICMREIT are formulated. A magnetic resonance imaging (MRI) pulse sequence is proposed for the realization of ICMREIT using the slice selection (z) gradient coil of MRI scanners. Considering the proposed MRI pulse sequence, relationship between the low frequency (LF) MR phase and the secondary magnetic field is expressed. Forward problem is solved using finite element method (FEM) for z and y gradient coils of MRI scanners. For the solution of the inverse problem, J-derivative and E-calculation image reconstruction algorithms are proposed and the performance of the algorithms is evaluated by using simulated measurements. Sensitivity and distinguishability analyses are performed in order to investigate imaging characteristics of ICMREIT. Phantom experiments are performed for physical realization of ICMREIT. Simulated and physical LF phase measurements have similar characteristics. Low sensitivity of LF phase measurements is thought to be the main reason for the quantitative difference between the simulated and experimental measurements and the major limitation of the method towards clinical applications. Using the LF phase measurements, current density and true conductivity images are reconstructed. Reconstructed current density and conductivity images show that ICMREIT is a safe and a potentially applicable medical imaging method. Reconstructed conductivity images are rough estimates of the simple phantoms and they exhibit qualitative reconstructions rather than quantitative images. Sensitivity of LF phase measurements and image reconstruction performance should be increased in order to use the method in clinical practice.  


Induced Current Magnetic Resonance Electrical Impedance Tomography with z-Gradient Coil
Eroglu, Hasan H.; Eyuboglu, Murat (2014-08-30)
Magnetic Resonance Electrical Impedance Tomography (MREIT) is a medical imaging method that provides images of electrical conductivity at low frequencies (0-1 kHz). In MREIT, electrical current is applied to the body via surface electrodes and corresponding magnetic flux density is measured by means of Magnetic Resonance (MR) phase imaging techniques. By utilizing the magnetic flux density measurements and surface potential measurements images of true conductivity distribution can be reconstructed. In order...
Induced Current Magnetic Resonance Electrical Conductivity Imaging With Oscillating Gradients
Eroglu, Hasan H.; Sadighi, Mehdi; Eyüboğlu, Behçet Murat (2018-07-01)
In this paper, induced current magnetic resonance electrical impedance tomography (ICMREIT) by means of current induction due to time-varying gradient fields of magnetic resonance imaging (MRI) systems is proposed. Eddy current and secondary magnetic flux density distributions are calculated for a numerical model composed of a z-gradient coil and a cylindrical conductor. An MRI pulse sequence is developed for the experimental evaluation of ICMREIT on a 3T MRI scanner. A relationship between the secondary ma...
Magnetic Resonance - Electrical Impedance Tomography (MR-EIT) Research at METU
Eyüboğlu, Behçet Murat (2006-09-01)
Following development of magnetic resonance current density imaging (MRCDI), magnetic resonance - electrical impedance tomography (MR-EIT) has emerged as a promising approach to produce high resolution conductivity images. Electric current applied to a conductor results in a potential field and a magnetic flux density distribution. Using a magnetic resonance imaging (MRI) system, the magnetic flux density distribution can be reconstructed as in MRCDI. The flux density is related to the current density distr...
Equipotential projection based magnetic resonance electrical impedance tomography (mr-eit) for high resolution conductivity imaging
Özdemir, Mahir Sinan; Eyüboğlu, Behçet Murat; Department of Electrical and Electronics Engineering (2003)
In this study, a direct reconstruction algorithm for Magnetic Resonance Electrical Impedance Tomography (MR-EIT) is proposed and experimentally implemented for high resolution true conductivity imaging. In MR-EIT, elec trical impedance tomography (EIT) and magnetic resonance imaging (MRI) are combined together. Current density measurements are obtained making use of Magnetic Resonance Current Density Imaging (MR-CDI) techniques and peripheral potential measurements are determined using conventional EIT tech...
Regional Image Reconstruction with Optimum Currents for MREIT - Evaluation on Shepp-Logan Conductivity Phantom
Eyüboğlu, Behçet Murat; Altunel, Haluk (2008-11-27)
In this study, an image reconstruction algorithm for magnetic resonance electrical impedance tomography (MREIT) is proposed to achieve maximum benefit of optimum current injection patterns. By doing so, considerable reduction in probing current amplitude could be possible. In the proposed algorithm, field of view (FOV) is divided into a number of segments. Image of each segment is reconstructed separately, based on measurements obtained using the best (optimum) current patterns, which maximize distinguishab...
Citation Formats
H. H. Eroğlu, “Induced current magnetic resonance electrical impedance tomography (ICMREIT) with low frequency switching of gradient fields,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.