Full-Wave Analysis of Planar Radiofrequency Coils and Coil Arrays with Assumed Current Distribution

For the analysis of single radiofrequency (RF) surface coils at frequencies commonly used for magnetic resonance imaging and spectroscopy, magnetostatic analysis often provides sufficiently accurate results. However, the availability of higher field whole body magnets and the widespread use of RF coil arrays have demonstrated the need for more accurate solutions. While more advanced approaches are available, such as the finite-element method or integral equation methods, commercial codes are not widely available and the techniques can be difficult to implement. This paper presents a computationally and analytically simple full-wave analysis method to determine the self and mutual impedances and magnetic fields of planar RF coils and coil arrays. The approach is formulated in the spectral domain and results in a computationally efficient method that includes the conductivity and permittivity of a planar load. Thus, high-field shielding effects are included. As described here, the method requires knowledge of the current distribution on the coils, which can be assumed to be constant in the case of simple rectangular or circular coil elements or determined from other methods such as equivalent circuit analysis in the case of more complicated structures. Complete expressions for the calculation of self and mutual impedances and the magnetic fields of circular and rectangular coils are provided. Examples are shown which demonstrate effects not modeled by quasistatics, including shielding effects and frequency-dependent field asymmetries. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 2–14, 2002.