June 18,  19,  20   2003
 
 
 

10:30 AM - Thursday, June 19, 2003 - Amphitheater Darboux

Jin Keun Seo

Departement of Mathematics
Yonsei University
Seoul 120-749, Korea

seoj@yonsei.ac.kr

Magnetic Resonance Electrical Impedance Tomography (MREIT): Imaging of Electrical Conductivity and Current Density

Numerous experimental findings have shown that different biological tissues in the human body have different electrical properties at the frequency range of tens of Hz to several MHz. The electrical conductivity and permittivity of a biological tissue change with cell concentration, cellular structure, molecular composition, membrane capacitance, and so on. Therefore, these properties manifest structural, functional, metabolic, and pathological conditions of the tissue providing valuable diagnostic information. Cross-sectional imaging of electrical conductivity distributions within a human body has been a research goal in Electrical Impedance Tomography (EIT). However, EIT suffers from the ill-posed characteristics of the corresponding inverse problem due primarily to nonlinearity and low sensitivity. In order to overcome this technical difficulty, we started looking at internal information so that we can transform the ill-posed problem into a well-posed one. This initiated the new research area called Magnetic Resonance Electrical Impedance Tomography (MREIT). In MREIT, we use a Magnetic Resonance Imaging (MRI) scanner to measure the induced magnetic flux density due to an injection current. We address the image reconstruction problem in MREIT as a well-posed inverse problem taking advantage of this additional internal information. For image reconstruction algorithms, we summarize the J-substitution algorithm where we use the internal current density obtained from the induced magnetic flux density. The main drawback of this method is the requirement of subject rotations to measure all three components of the induced magnetic flux density. We introduce two other algorithms that utilize only one component of the induced magnetic flux density thereby removing the subject rotation procedure. Once we have reconstructed images of conductivity distributions, we can produce images of internal current density distributions for any given injection currents. Showing numerical and experimental results in MREIT, we suggest MREIT for static imaging of cross-sectional conductivity distributions leaving EIT for dynamic imaging and lesion detections.