Imaging Conductivity Distribution Of Human Brain Tissues By Induced Current Magnetic Resonance Electrical Impedance Tomography

Information about electrical conductivity distributions of the human brain tissues is scientifically significant and practically important for many purposes, such as the study of brain functions and the diagnosis of clinical diseases.In electrical impedance tomography (EIT) and magnetic resonance electrical impedance tomography (MREIT), the injected current can not reach the inner brain tissues because of the shielding effect of the skull. The induced current magnetic resonance electrical impedance tomography (IC-MREIT) is a novel, noninvasive imaging technique developed after the technique of MREIT. Since this technique has great promise to overcome the drawbacks of EIT and MREIT, the image of electrical conductivity distribution with high accuracy and resolution can be obtained for clinical medicine.The basic principle, the present situation and the development perspect of EIT and MREIT were introduced based on two excitation methods, namely, the injected current method and the induced current method. Then, the research meaning of imaging the conductivity distributions of the brain tissues was illustrated.The sensitivity matrix method was introduced into IC-MREIT to reconstruct the isotropic, but inhomogeneous, conductivity distributions of brain tissues. Also, the influences of system parameters on the property of sensitivity matrix were analyzed. The obtained conclusions can provide meaningful guide and reference for the future experimental and clinical applications.Based on the basic electromagnetic equation, the conclusion that the IC-MREIT can reconstruct the absolute conductivity distribution without any boundary voltage measurement was derived and the IC-MREIT J-substitution algorithm was proposed. By providing physical insight into the charge accumulating on the interfaces, the convergence characteristic of the reconstruction algorithm was analyzed. A series of computer simulation studies were conducted on a three-sphere head model and a realistic head model and the simulation results are encouraging.Considering the fact that the conductivities of most brain tissues are anisotropic, a two-step IC-MREIT reconstruction algorithm was developed to image the anisotropic conductivity distribution inside the object. The simulation results conducted on the three-sphere head model and the five-compartment realistic head model suggest that, with the aid of some priori information, the present reconstruct algorithm can image the conductivity distributions of complicated brain tissues with high accuracy.