Figure 2 shows the setup for all phantom experiments. The saline gel phantom consisted of a 39 cm × 26 cm × 8 cm tub filled with a mixture of distilled water, 8 g/L Polyacrylic Acid (Aldrich Chemical) and 0.7 g/L sodium chloride (23 (link)) to achieve a conductivity of approximately 0.5 S/m and relative permittivity of approximately 88 (DAK, Speag). The phantom was doped with nickel chloride to reduce the T1 to approximately 300 ms to enable faster imaging. The toroidal transceiver was interfaced to the 1.5T scanner using a transmit-receive (T/R) switch. During transmit, the T/R switch connects the toroidal transceiver to a dedicated power amplifier to induce low levels of RF current in the catheter/wire for visualization. A bi-directional coupler (Werlatone C7149-12) in the transmit chain measures forward and reverse power delivered to the toroidal transceiver. During receive, the T/R switch connects the toroid signal to the surface-coil port of the scanner for image acquisition. A Medusa USB console (24 (link)) controls the synchronous RF transmit and data receive. A photonically-powered, optically-coupled toroidal RF current sensor (described below) located on the wire outside the phantom monitors induced RF current levels.