Ideal Current Pattern Analysis of Transmit Resonators in Magnetic Resonance Imaging

The shorter wavelength of RF transmit chain at ultrahigh field $(\gt 3\mathrm{T})$ magnetic resonance imaging (MRI) inherently determines the inhomogeneous transverse magnetic field $\left(B_{1}^{+}\right)$ produced by classic birdcage resonator, which was designed under quasi-static principle. To investigate the optimal current patterns of cavity resonators at ultra-high field MRI, we introduced a dyadic Green's function (DGF) based simulation framework. The genetic algorithm is used to optimize the current weights of spherical harmonics for uniform $B_{1}^{+}$. Finally, optimized $B_{1}^{+}$fields are calculated. The corresponding ideal current patterns of the optimized $B_{1}^{+}$field under different field strengths of MRI are analyzed and summarized.