Imaging electric properties of human brain tissues by B1 mapping: A simulation study

The electric properties (EPs) of biological tissues, i.e., the electric conductivity and permittivity, can provide important diagnostic information in cancer detection and characterization. The conductivity also plays an important role in specific absorption rate (SAR) calculation, which is a major concern in high-field Magnetic Resonance Imaging (MRI). In MRI systems the radio frequency (RF) radiation is dependent on the object's EPs by Maxwell Equations, and we can reconstruct the EPs distribution by measuring the active transverse component of the applied rotating magnetic field in MRI systems (known as B1-mapping). Applying previously proposed Dual-excitation algorithm, we conducted a series of computer simulations on a three-dimensional five-tissue anatomically accurate head model using the Finite Element Method (FEM). The reconstruction results utilizing several RF coils were examined and compared, and the present simulation results indicate that the TEM coil could produce the optimal result. The Specific energy Absorption Rate (SAR) within the head was also estimated using the reconstructed electric properties distribution, and the promising results suggest our approach might provide an efficient way for in-vivo SAR determination in high field MRI.