An inverse method for radio frequency phased array coil design in magnetic resonance imaging equipment

Abstract

Magnetic resonance imaging is a popular non-invasive technique for investigating soft tissue structures within the human body. Many design methods now exist for their principle hardware components, such as the radio frequency (RF) coils. A popular RF coil type is the RF phased array, comprised of many closely spaced coils covering a large volume. A time harmonic inverse method is presented for the theoretical design of RF phased arrays. The method allows any array size to be considered where the focus is on optimal coil geometry and position of individual coils. An ill-conditioned integral equation is solved using a regularisation strategy in which the error between induced and target magnetic fields is minimised along with an additional constraint related to the curvature of the coil windings. The method is demonstrated for a number of design considerations and includes the ability to focus the RF field to arbitrary locations within the coil volume. The effect of the choice of magnetic field polarisation direction is also investigated using the model.