RF coil design for low and high field MRI: Numerical methods and measurements

Several clinical magnetic resonance applications at 1.5 T and higher field strengths require a careful selection of the RadioFrequency (RF) coil design to optimize the RF spatial distribution and sensitivity. Specifically, two basic requirements must be fulfilled for obtaining high quality images: in the transmission mode, RF coils must be able to produce a uniform magnetic field in the volume of interest so that the nuclei can be properly excited; in the receiving mode, a high signal to noise ratio is needed, and the coil must be able to collect the signal emitted by the nuclei with better sensitivity throughout the volume of interest. A number of analytical and numerical methods are reported in the literature to simulate the RF field distributions of surface and volume coils. In this work, we compared the performances of two computational methods (Method of Moments and Finite Elements Method), considering the modelling of both surface (single loop, figure of eight coil - FO8, dual loop) and volume (TEM) coils. Low (1.5 T) and high (7 T) field operating regimes have been analysed. Measurements obtained on the workbench and with a 1.5 T scanner are used for validation.