Standalone RF Self-Interference Cancellation System for In-Vivo Simultaneous Transmit and Receive (STAR) MRI

Demonstrated is a standalone RF self-interference canceller for simultaneous transmit and receive (STAR) magnetic resonance imaging (MRI) at 1.5T. Standalone STAR cancels the leakage signal directly coupled between transmit and receive RF coils. A cancellation signal, introduced by tapping the input of a transmit coil with a power divider, is manipulated with voltage-controlled attenuators and phase shifters to match the leakage signal in amplitude, 180 degrees out of phase, to exhibit high isolation between the transmitter and receiver. The cancellation signal is initially generated by a voltage-controlled oscillator (VCO); therefore, it does not require any external RF or synchronization signals from the MRI console for calibration. The system employs a field programmable gate array (FPGA) with an on-board analog to digital converter (ADC) to calibrate the cancellation signal by tapping the receive signal, which contains the leakage signal. Once calibrated, the VCO is disabled and the transmit signal path switches to the MRIconsole for STAR MR imaging. To compensate for the changes of parameters in RF sequences after the automatic calibration and to further improve isolation, a wireless user board that uses an ESP32 microcontroller was built to communicate with the FPGA for final fine-tuning of the output state. The standalone STAR system achieved 74.2 dB of isolation with a 94 second calibration time. With such high isolation, in-vivo MR images were obtained with approximately 40 mW of RF peak power.

Automated summary

In this study, a standalone RF self-interference canceller for 1.5T simultaneous transmit and receive (STAR) magnetic resonance imaging (MRI) was developed. The system achieved high isolation by manipulating a cancellation signal with voltage-controlled attenuators and phase shifters to match the leakage signal between transmit and receive RF coils. The cancellation signal was initially generated by a voltage-controlled oscillator (VCO) and calibrated by tapping the receive signal. The system achieved 74.2 dB of isolation with a 94-second calibration time. In-vivo MR images were obtained with approximately 40 mW of RF peak power. Evaluation: 9/10.