RF Coils of Magnetic-Resonance Imaging as Phased Arrays

摘要

Both field-theoretical and circuit-based analyses of field distribution and element coupling and loading in MRI-RF coils are presented and/or revisited in this contribution. Emphasis is put on high-field operations, in which the geometrical dimensions of the coil become comparable to the Larmor wavelength. In the circuit-based analysis the characteristic properties of circulant matrices, which describe periodic structures with ring-type coupling, are utilized. This enables the proper and targeted control of the element coupling instead of unnecessarily trying to minimize or even eliminate it. It also results in useful equations for the calculation of the coil loading, which is needed for the optimization of its operation in both transmitting and receiving scenarios. With its fundamental nature, the paper presents and/or revisits physical insights and useful design equations. Therefore, no simulation or measurement results are included.