An inverse method for designing RF phased array coils in MRI-theoretical considerations

Abstract

Phased array coils afford a number of advantages over RF volume coils, including a high SNR over a large field of view. In this paper, a time-harmonic inverse method is presented for the theoretical design of RF phased arrays. The method allows any array size to be considered, for which a homogeneous magnetic field is desired within some spherical target region within the coils. An ill-conditioned integral equation is solved using regularization, whereby the error between induced and target magnetic fields is minimized along with an additional constraint related to the curvature of the coil windings. The ability to focus the RF field to arbitrary locations within the coil volume is incorporated into the model and a number of examples are displayed. Attention is also given to the polarization of the induced field, with the direction of linear polarization investigated along with circular polarization. Phased arrays comprising smooth windings that are able to induce highly homogeneous magnetic fields are displayed and discussed for a range of array sizes, and for several different field focusing and polarization considerations.