Investigation in Radio Frequency Magnetic Field Mapping Towards Tissue Magnetic Resonance Electric Properties Tomography

The electric properties of tissue can potentially be used as an additional diagnostic parameter, e.g., in tumor diagnosis. In this study, the radio frequency magnetic field mapping in the Magnetic Resonance Imaging and also the Magnetic Resonance Electric Properties Tomography is researched. The distortion of the magnetic field generated by the radio frequency coil, named as B1 inhomogeneity, is analyzed by simulation and measurement methods. The information of electric conductivity and dielectric constant of human body is included in the changement of the B1 distribution. The principle for the circular presentation of the high frequency time-harmonic wave and its non-uniformity in field amplitude and orientation is derived. According to a standard spin echo imaging sequence, the excitation and receiver fields are related the signal intensity for post calculation. For the custom-made birdcage coil, the radio frequency magnetic field was simulated by parameterized finite element method and MRI measurements. The length and diameter of the coil are 0.3 m and 0.48 m, respectively. The deviations of amplitude uniform from no-load to phantom-loaded case in simulation and experiment are -7.0% and 7.4%, which indicate the electric properties influence. The B1 map would be another potential imaging mechanism in MRI technology after the proton density and relaxation time alternatives.