Imaging anisotropic conductivity with induced current magnetic resonance electrical impedance tomography (ICMREIT)

In gradient coil based induced current magnetic resonance electrical impedance tomography (ICMREIT), gradient coils of a conventional magnetic resonance imaging (MRI) scanner are excited with time varying waveforms embedded in an MRI pulse sequence [1], [2], [3]. As a result of the excitation, low frequency (LF) eddy current is induced in the volume conductor media being imaged which accumulates phase to MR signal. By measuring and post-processing the LF phase of the eddy current, LF conductivity images are reconstructed [1], [2], [3]. In [1], ICMREIT is experimentally realized with by excitation of the slice selection (z) gradient coil of a clinical MRI scanner and conductivity images of phantoms with isotropic conductivity are satisfactorily reconstructed. However, biological tissues have anisotropic conductivity distributions. In order to reconstruct anisotropic conductivity distributions, coils with linearly independent primary magnetic fields are required. In ICMREIT, phase encoding (y) gradient coil of an MRI scanner can also be used in addition to the z-gradient coil. In this study, we demonstrate numerical models including the z and y-gradient coils of an MRI scanner and a cylindrical volume conductor. We utilize distinguishability analysis in order to compare the abilities of z and y-gradient coil based ICMREIT systems to differentiate conductivity perturbations from the background [3]. We propose a conductivity image reconstruction algorithm and reconstruct conductivity images by using simulated and physical measurements obtained for a cylindrical volume conductor including an inhomogeneity. The results of the distinguishability analysis, the simulation and the experimental results show that utilizing the z-gradient coil is advantageous than using the y-gradient coil