Optically controlled on-coil amplifier with RF monitoring feedback

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Engineering
• Biomedical Engineering

Background:

• High-field MRI requires precise control of radiofrequency (RF) transmission for uniform excitation.
• Existing multi-channel RF transmission methods face challenges in maintaining signal integrity and safety.
• On-coil amplifiers offer potential for improved RF field control but require robust monitoring and feedback mechanisms.

Purpose of the Study:

• To develop and evaluate an optically controlled on-coil amplifier system for MRI.
• To enable safe and real-time monitoring of RF signal phase and amplitude during multi-channel transmission.
• To facilitate precise control of RF transmission fields for uniform excitation at high magnetic fields.

Main Methods:

• A 4-channel prototype system was developed for sensing, down-sampling, digitizing, and optically transmitting RF transmit signals.
• The system utilized a remote PC to control the on-coil amplifiers based on monitored signal parameters.
• Performance was assessed using benchtop measurements and 7 Tesla (7T) MRI experiments.

Main Results:

• The monitored amplitude and phase exhibited high stability with low standard deviations (0.061 µT and 0.0073 rad).
• The feedback control system achieved inter-channel phase and B1 amplitude adjustments within two iterations.
• Feasibility of safe and accurate multi-channel RF transmission and monitoring at high field was demonstrated in MRI experiments.

Conclusions:

• A 4-channel transceiver system with optically controlled on-coil amplifiers and RF monitoring was successfully demonstrated.
• This approach provides safe and precise control of RF transmission fields, crucial for uniform excitation in high-field MRI.
• The developed system represents a significant advancement for high-field MRI applications requiring controlled RF transmission.