Optically controlled on‐coil amplifier with RF monitoring feedback

Purpose To develop a new optically controlled on‐coil amplifier that facilitates safe use of multi‐channel radiofrequency (RF) transmission in MRI by real‐time monitoring of signal phase and amplitude. Methods Monitoring was carried out with a 4‐channel prototype system by sensing, down sampling, digitizing, and optically transmitting the RF transmit signal to a remote PC to control the amplifiers. Performance was evaluated with benchtop and 7 T MRI experiments. Results Monitored amplitude and phase were stable across repetitions and had standard deviations of 0.061 μT and 0.0073 rad, respectively. The feedback system allowed inter‐channel phase and B1 amplitude to be adjusted within two iterations. MRI experiments demonstrated the feasibility of this approach to perform safe and accurate multi‐channel RF transmission and monitoring at high field. Conclusion We demonstrated a 4‐channel transceiver system based on optically controlled on‐coil amplifiers with RF signal monitoring and feedback control. The approach allows the safe and precise control of RF transmission fields, required to achieve uniform excitation at high field. Magn Reson Med 79:2833–2841, 2018. © 2017 International Society for Magnetic Resonance in Medicine.