Radially Extended 3D Birdcage Antenna for MRI With Loop-Type Legs and Connection to the Shield

A novel radially extended 3D birdcage (BC) coil antenna was designed, simulated, and optimized for a cylindrical dielectric phantom at 4.7 T. The 3D birdcage consists of a classical birdcage with additional protrusions toward the inside and connections to the shield. To overcome the huge computational burden of the optimization process using the particle swarm optimization (PSO) method, an in-house method of moment (MoM) code exploiting the symmetry of the structure has been developed. The code produces open-circuit embedded element patterns and makes use of a Schur complement to analyze the effects of passive loads, in the presence of a phantom. The simulation results have been verified with the use of commercial software. The proposed 3D BC coil showed a 34 % improvement in the homogeneity of
$B_{1}^{+}$
and a 37 % reduction in the peak specific absorption rate (SAR), compared with a conventional BC coil.