Computational analysis of the high pass birdcage resonator: finite difference time domain simulations for high-field MRI

In this work, a finite difference time domain (FDTD) algorithm is validated at 1.5 tesla using the standard GE Signa quadrature head coil and a muscle phantom. The electrical characteristics of the birdcage head coil are then calculated for the linear and quadrature cases. Unlike previous computational analysis which assume idealized currents on the end rings and the struts of the resonator, a complete computational analysis is provided. This treatment considers the coupling between the resonator and the sample and includes a real coil excitation, a complete current derivation, and a thorough description of both B-1 fields and RF radiation. With this improvement, electromagnetic phenomena such as radiation, standing wave currents on the wires, and field inhomogeneities due to interactions between the coil and the load inside the coil are observed. At 200 MHz, it is demonstrated that this particular coil does not work well due to radiation and non-uniformities on the struts of the device. Also, at this frequency magnetic field inhomogeneities become large when the coil is loaded with a phantom.