Controlling induced currents in guidewires using parallel transmit

Introduction: Conductive structures, such as guidewires and implanted device leads, present a safety hazard in MRI. The coupling between these structures and the RF transmit field can result in currents being induced, which can lead to dangerous heating [1, 2]. In previous work [3], it was shown that the magnitude and phase of current induced in a wire depends on the position of the RF coil with respect to the wire. This led us to investigate the feasibility of using parallel transmit with an array of surface coils to excite the imaging volume, without inducing current in a guidewire. In this work, we show that it is possible to choose parallel transmit coil weightings such that we can control the current induced in a guidewire. Furthermore, we show that only a single transmit mode induces significant current, while the other “null modes” induce low current levels. The null transmit modes are also shown to still provide adequate excitation to visualize the guidewire and surrounding volume.