Simultaneous imaging of dual‐frequency electrical conductivity using a combination of MREIT and MREPT

Chauhan

IEEE Trans. Med. Imaging

et al. 2015

Self Cite

Electrical conductivities of biological tissues show frequency-dependent behaviors, and these values at different frequencies may provide clinically useful diagnostic information. MR-based tissue property mapping techniques such as magnetic resonance electrical impedance tomography (MREIT) and magnetic resonance electrical property tomography (MREPT) are widely used and provide unique conductivity contrast information over different frequency ranges. Recently, a new method for data acquisition and reconstruction for low- and high-frequency conductivity images from a single MR scan was proposed. In this study, we applied this simultaneous dual-frequency range conductivity mapping MR method to evaluate its utility in a designed phantom and two in vivo animal disease models. Magnetic flux density and B(1)(+) phase map for dual-frequency conductivity images were acquired using a modified spin-echo pulse sequence. Low-frequency conductivity was reconstructed from MREIT data by the projected current density method, while high-frequency conductivity was reconstructed from MREPT data by B(1)(+) mapping. Two different conductivity phantoms comprising varying ion concentrations separated by insulating films with or without holes were used to study the contrast mechanism of the frequency-dependent conductivities related to ion concentration and mobility. Canine brain abscess and ischemia were used as in vivo models to evaluate the capability of the proposed method to identify new electrical properties-based contrast at two different frequencies. The simultaneous dual-frequency range conductivity mapping MR method provides unique contrast information related to the concentration and mobility of ions inside tissues. This method has potential to monitor dynamic changes of the state of disease.

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Frequency-Dependent Conductivity Contrast for Tissue Characterization Using a Dual-Frequency Range Conductivity Mapping Magnetic Resonance Method

Chauhan

IEEE Trans. Med. Imaging

et al. 2015

Self Cite

Magnetic Resonance in Med

“…Combining the proposed method with the convection reaction-based MREIT method (54), one can image the conductivity simultaneously at frequencies below a few kHz and at Larmor frequency, such as the recently published hybrid methods (55,56).…”

Section: Discussionmentioning

confidence: 99%

Gradient‐based electrical conductivity imaging using MR phase

Gürler

Ider

2016

165

Purpose: To develop a fast, practically applicable, and boundary artifact free electrical conductivity imaging method that does not use transceive phase assumption, and that is more robust against the noise. Theory: Starting from the Maxwell's equations, a new electrical conductivity imaging method that is based solely on the MR transceive phase has been proposed. Different from the previous phase based electrical properties tomography (EPT) method, a new formulation was derived by including the gradients of the conductivity into the equations. Methods: The governing partial differential equation, which is in the form of a convection-reaction-diffusion equation, was solved using a three-dimensional finite-difference scheme. To evaluate the performance of the proposed method numerical simulations, phantom and in vivo human experiments have been conducted at 3T. Results: Simulation and experimental results of the proposed method and the conventional phase-based EPT method were illustrated to show the superiority of the proposed method over the conventional method, especially in the transition regions and under noisy data. Conclusion: With the contributions of the proposed method to the phase-based EPT approach, a fast and reliable electrical conductivity imaging appears to be feasible, which is promising for clinical diagnoses and local SAR estimation. INTRODUCTIONImaging electrical properties (EPs, conductivity ðsÞ and permittivity ðeÞ) of tissues can potentially be useful in several applications. For example, conductivity is a key parameter in the calculation of the specific absorption rate (SAR) map of a patient, which is a crucial issue at high field MRI. Additionally, EPs can be used for diagnostic purposes. In in vivo studies, especially in oncology, it has been shown that the conductivity of a tumor region increases (1-3). Furthermore, EPs may also be used in therapy monitoring (or planning) such as transcranial magnetic stimulation (TMS) (4), hyperthermia treatment (5), and radiofrequency (RF) ablation (6).Over the years, many methods have been proposed to image EPs at various frequencies. For low-frequency applications (1 kHz to 1 MHz), electrical impedance tomography (EIT) and magnetic induction tomography (MIT) have been developed to calculate EPs (7-12). In these methods, sinusoidal currents are either injected into tissue through surface electrodes (EIT) or induced in the tissue using external coils (MIT), and induced voltages are measured between surface electrodes. The current-voltage data sets are used to calculate impedance maps, but the resulting images lack spatial resolution because of the insensitivities of the surface measurements to inner regions. To improve the spatial resolution, magnetic resonance electrical impedance tomography (MREIT) has been proposed (13)(14)(15)(16)(17)(18)(19)(20). In MREIT, additional magnetic field is generated by injecting currents into the tissue through surface electrodes, and this additional magnetic field is then measured using an MRI scanner to reconstruct ...

“…In order to giving full play to the advantages of EIT functional imaging, scholars used the methods of combining EIT with other detection means to increase the amount of information and improve the resolution. There were two kinds of typical approaches: one is the combination of EIT and Magnetic Resonance Imaging (MRI) techniques, such as Magnetic Resonance Electrical Impedance Tomography (MREIT) [4] ; another one is a combination of EIT and ultrasound technology, such as Magneto Acoustic Tomography (MAT) and Magneto-Acoustic-Electrical Tomography (MAET) [5,6] . The combination technologies could effectively overcome the serious illness of the EIT inverse problem and the low resolution problem, but also brought new problems, which are the RF shielding effect in the strong magnetic field when the electrode excitation is used in MREIT; the poor anti-noise performance of imaging algorithm in MREIT [7,8] ; the difficulty of further improving resolutions in MAT and MAET which are affected by the factors such as the number of probe [9] .…”

Section: Introductionmentioning

confidence: 99%

Electrical Impedance Tomography Based on Vibration Excitation in Magnetic Resonance System

Li¹,

Liu²,

Xin³

et al. 2017

dtetr

Abstract. Because of low resolution, Electrical Impedance Tomography (EIT) had been criticized by the experts and scholars. Although the resolution of the Magnetic Resonance Electrical Impedance Tomography (MREIT) which is combined EIT with Magnetic Resonance Imaging (MRI) technology and the resolution of the Magneto-Acoustic-Electrical Tomography (MAET) which is combined EIT with ultrasonic technology are improved, there are still existing problems, which are the electrode RF shielding in MREIT, the difficulty of further improving resolution in MAET. Combining the technologies of MRI and MAET for mutual advantage, this paper proposed a new method of Magnetic Resonance Motional-Electrical Tomography (MRMET) based on the principle of MAET. The software Comsol and Matlab were used to establish a two-dimensional simulation model, and the forward problem and inverse problem of MRMET were researched on the simulation works. The simulation results could reflect the conductivity distribution inside the simulation model, and MRMET could solve the problems of the EIT combination technologies.