Tomographic imaging of electrical conductivity and permittivity of tissues may be used for diagnostic purposes as well as for estimating local specific absorption rate (SAR) distributions. Magnetic Resonance Electrical Properties Tomography (MREPT) aims at noninvasively obtaining conductivity and permittivity images at RF frequencies of MRI systems. MREPT algorithms are based on measuring the B 1 field which is perturbed by the electrical properties of the imaged object. In this study, the relation between the electrical properties and the measured B + 1 field is formulated, for the first time as, the well-known convection-reaction equation. The suggested novel algorithm, called "cr-MREPT", is based on the solution of this equation, and in contrast to previously proposed algorithms, it is applicable in practice not only for regions where electrical properties are relatively constant but also for regions where they vary. The convection-reaction equation is solved using a triangular mesh based finite difference method and also finite element method (FEM).The convective field of the convection-reaction equation depends on the spatial derivatives of the B + 1 field. In the regions where the magnitude of convective field is low, a spot-like artifact is observed in the reconstructed conductivity and dielectric permittivity images. For eliminating this artifact, two different methods are developed, namely "constrained cr-MREPT" and "double-excitation cr-MREPT". In the constrained cr-MREPT method, in the region where the magnitude of convective field is low, the electrical properties are reconstructed by neglecting the convective term in the equation. The obtained solution is used as a constraint for solving electrical properties in the whole domain. In the double-excitation cr-MREPT method, two B 1 excitations, which create two convective field distributions having low magnitude of convective field in different iii iv locations, are applied separately. The electrical properties are then reconstructed simultaneously using data from these two applied B + 1 field.These methods are tested with both simulation and experimental data from phantoms. As seen from results, successful electrical property reconstructions are obtained in all regions including electrical property transition region. The performance of cr-MREPT method against noise is also investigated.

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 ...

Design of magnetic resonance imaging (MRI) radiofrequency (RF) coils using lumped circuit modeling based techniques begins to fail at high frequencies, and therefore more accurate models based on the electromagnetic field calculations must be used. Field calculations are also necessary to understand the interactions between the RF field and the subject inside the coil. Furthermore, observing the resonance behavior of the coil and the fields at the resonance frequencies have importance for design and analysis. In this study, finite element method (FEM) based methods have been proposed for accurate time-harmonic electromagnetic simulations, estimation of the tuning capacitors on the rungs or end rings, and the resonant mode analysis of the birdcage coils. Capacitance estimation was achieved by maximizing the magnitude of the port impedance at the desired frequency while simultaneously minimizing the variance of RF magnetic field in the region of interest. In order for the proposed methods to be conveniently applicable, two software tools, resonant mode and frequency domain analyzer (RM-FDA) and Optimum Capacitance Finder (OptiCF), were developed. Simulation results for the validation and verification of the software tools are provided for different cases including human head simulations. Additionally, two handmade birdcage coils (low-pass and high-pass) were built and resonance mode measurements were made. Results of the software tools are compared with the measurement results as well as with the results of the lumped circuit modeling based method. It has been shown that the proposed software tools can be used for accurate simulation and design of birdcage coils.