Design of Crisscrossed Double-Layer Birdcage Coil for Improving B₁⁺Field Homogeneity for Small-Animal Magnetic Resonance Imaging at 300 MHz

We design a crisscrossed double-layer birdcage (DLBC) coil by modifying the coil geometry of a standard single-layer BC (SLBC) coil to enhance the homogeneity of transmitting magnetic flux density (B 1 + ) along the main magnetic field (B 0 )-direction for small-animal magnetic resonance imaging (MRI) at 300 MHz. The performance assessment of the crisscrossed DLBC coil is conducted by computational analysis with the finitedifference time domain method (FDTD) and compared with SLBC coil in terms of the B 1 and the B 1 + distribution. As per the computational calculation studies, the mean value in the two-dimensional B 1 + map obtained at the mid-axial slice with the proposed DLBC coil is slightly lower than that obtained with the SLBC coil, but the B 1 + value of the DLBC coil in the outermost plane (40 mm away from the central plane) shows improvements of 19.3% and 24.8% over the SLBC coil B 1 + value when simulating a spherical phantom and realistic mouse body modeling. These simulation results indicate that, the B 1 + homogeneity along the z-direction was improved by using DLBC configuration. Our approach enables B 1 + homogeneity improvement along the zdirection, and it can also be applied to ultra-high field (UHF) MRI systems.